In this document
+-
+
-
+ Overview
+
-
+
- + Accessing a provider + +
- + Content URIs + +
+ -
+ Retrieving Data from the Provider
+
-
+
- + Requesting read access permission + +
- + Constructing the query + +
- + Displaying query results + +
- + Getting data from query results + +
+ - + Content Provider Permissions + +
-
+ Inserting, Updating, and Deleting Data
+
-
+
- + Inserting data + +
- + Updating data + +
- + Deleting data + +
+ - + Provider Data Types + +
-
+ Alternative Forms of Provider Access
+
-
+
- + Batch access + +
- + Data access via intents + +
+ - + Contract Classes + +
- + MIME Type Reference + +
Key classes
+-
+
- + {@link android.content.ContentProvider} + +
- + {@link android.content.ContentResolver} + +
- + {@link android.database.Cursor} + +
- + {@link android.net.Uri} + +
Related Samples
+-
+
- + + Cursor (People) + +
- + + Cursor (Phones) + +
See also
+-
+
- + + Creating a Content Provider + +
- + + Calendar Provider + +
+ A content provider manages access to a central repository of data. The provider and + is part of an Android application, which often provides its own UI for working with + the data. However, content providers are primarily intended to be used by other + applications, which access the provider using a provider client object. Together, providers + and provider clients offer a consistent, standard interface to data that also handles + inter-process communication and secure data access. +
++ This topic describes the basics of the following: +
+-
+
- How content providers work. +
- The API you use retrieve data from a content provider. +
- The API you use to insert, update, or delete data in a content provider. +
- Other API features that facilitate working with providers. +
Overview
++ A content provider presents data to external applications as one or more tables that are + similar to the tables found in a relational database. A row represents an instance of some type + of data the provider collects, and each row in the column represents an individual piece of + data collected for an instance. +
++ For example, one of the built-in providers in the Android platform is the user dictionary, which + stores the spellings of non-standard words that the user wants to keep. Table 1 illustrates what + the data might look like in this provider's table: +
++ Table 1: Sample user dictionary table. +
+| word | +app id | +frequency | +locale | +_ID | +
|---|---|---|---|---|
| mapreduce | +user1 | +100 | +en_US | +1 | +
| precompiler | +user14 | +200 | +fr_FR | +2 | +
| applet | +user2 | +225 | +fr_CA | +3 | +
| const | +user1 | +255 | +pt_BR | +4 | +
| int | +user5 | +100 | +en_UK | +5 | +
+ In table 1, each row represents an instance of a word that might not be
+ found in a standard dictionary. Each column represents some data for that word, such as the
+ locale in which it was first encountered. The column headers are column names that are stored in
+ the provider. To refer to a row's locale, you refer to its locale column. For
+ this provider, the _ID column serves as a "primary key" column that
+ the provider automatically maintains.
+
+ Note: A provider isn't required to have a primary key, and it isn't required
+ to use _ID as the column name of a primary key if one is present. However,
+ if you want to bind data from a provider to a {@link android.widget.ListView}, one of the
+ column names has to be _ID. This requirement is explained in more detail in the
+ section Displaying query results.
+
Accessing a provider
++ An application accesses the data from a content provider with + a {@link android.content.ContentResolver} client object. This object has methods that call + identically-named methods in the provider object, an instance of one of the concrete + subclasses of {@link android.content.ContentProvider}. The + {@link android.content.ContentResolver} methods provide the basic + "CRUD" (create, retrieve, update, and delete) functions of persistent storage. +
++ The {@link android.content.ContentResolver} object in the client application's + process and the {@link android.content.ContentProvider} object in the application that owns + the provider automatically handle inter-process communication. + {@link android.content.ContentProvider} also acts as an abstraction layer between its + repository of data and the external appearance of data as tables. +
++ Note: To access a provider, your application usually has to request specific + permissions in its manifest file. This is described in more detail in the section + Content Provider Permissions +
++ For example, to get a list of the words and their locales from the User Dictionary Provider, + you call {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()}. + The {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + query()} method calls the + {@link android.content.ContentProvider#query(Uri, String[], String, String[], String) + ContentProvider.query()} method defined by the User Dictionary Provider. The following lines + of code show a + {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()} call: +
+
+// Queries the user dictionary and returns results +mCursor = getContentResolver().query( + UserDictionary.Words.CONTENT_URI, // The content URI of the words table + mProjection, // The columns to return for each row + mSelectionClause // Selection criteria + mSelectionArgs, // Selection criteria + mSortOrder); // The sort order for the returned rows ++
+ Table 2 shows how the arguments to + {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + query(Uri,projection,selection,selectionArgs,sortOrder)} match an SQL SELECT statement: +
++ Table 2: Query() compared to SQL query. +
+| query() argument | +SELECT keyword/parameter | +Notes | +
|---|---|---|
Uri |
+ FROM table_name |
+ Uri maps to the table in the provider named table_name. |
+
projection |
+ col,col,col,... |
+
+ projection is an array of columns that should be included for each row
+ retrieved.
+ |
+
selection |
+ WHERE col = value |
+ selection specifies the criteria for selecting rows. |
+
selectionArgs |
+
+ (No exact equivalent. Selection arguments replace ? placeholders in the
+ selection clause.)
+ |
+ |
sortOrder |
+ ORDER BY col,col,... |
+
+ sortOrder specifies the order in which rows appear in the returned
+ {@link android.database.Cursor}.
+ |
+
Content URIs
++ A content URI is a URI that identifies data in a provider. Content URIs + include the symbolic name of the entire provider (its authority) and a + name that points to a table (a path). When you call + a client method to access a table in a provider, the content URI for the table is one of + the arguments. +
++ In the preceding lines of code, the constant + {@link android.provider.UserDictionary.Words#CONTENT_URI} contains the content URI of + the user dictionary's "words" table. The {@link android.content.ContentResolver} + object parses out the URI's authority, and uses it to "resolve" the provider by + comparing the authority to a system table of known providers. The + {@link android.content.ContentResolver} can then dispatch the query arguments to the correct + provider. +
++ The {@link android.content.ContentProvider} uses the path part of the content URI to choose the + table to access. A provider usually has a path for each table it exposes. +
++ In the previous lines of code, the full URI for the "words" table is: +
++content://user_dictionary/words ++
+ where the user_dictionary string is the provider's authority, and
+ words string is the table's path. The string
+ content:// (the scheme) is always present,
+ and identifies this as a content URI.
+
+ Many providers allow you to access a single row in a table by appending an ID value
+ to the end of the URI. For example, to retrieve a row whose _ID is
+ 4 from user dictionary, you can use this content URI:
+
+Uri singleUri = ContentUri.withAppendedId(UserDictionary.Words.CONTENT_URI,4); ++
+ You often use id values when you've retrieved a set of rows and then want to update or delete + one of them. +
++ Note: The {@link android.net.Uri} and {@link android.net.Uri.Builder} classes + contain convenience methods for constructing well-formed Uri objects from strings. The + {@link android.content.ContentUris} contains convenience methods for appending id values to + a URI. The previous snippet uses {@link android.content.ContentUris#withAppendedId(Uri, long) + withAppendedId()} to append an id to the UserDictionary content URI. +
+ + + +Retrieving Data from the Provider
++ This section describes how to retrieve data from a provider, using the User Dictionary Provider + as an example. +
++ For the sake of clarity, the code snippets in this section call + {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()} on the "UI thread"". In actual code, however, you should + do queries asynchronously on a separate thread. One way to do this is to use the + {@link android.content.CursorLoader} class, which is described + in more detail in the + Loaders guide. Also, the lines of code are snippets only; they don't show a complete + application. +
++ To retrieve data from a provider, follow these basic steps: +
+-
+
- + Request the read access permission for the provider. + +
- + Define the code that sends a query to the provider. + +
Requesting read access permission
+
+ To retrieve data from a provider, your application needs "read access permission" for the
+ provider. You can't request this permission at run-time; instead, you have to specify that
+ you need this permission in your manifest, using the
+
+ <uses-permission> element and the exact permission name defined by the
+ provider. When you specify this element in your manifest, you are in effect "requesting" this
+ permission for your application. When users install your application, they implicitly grant
+ this request.
+
+ To find the exact name of the read access permission for the provider you're using, as well + as the names for other access permissions used by the provider, look in the provider's + documentation. +
++ The role of permissions in accessing providers is described in more detail in the section + Content Provider Permissions. +
+
+ The User Dictionary Provider defines the permission
+ android.permission.READ_USER_DICTIONARY in its manifest file, so an
+ application that wants to read from the provider must request this permission.
+
Constructing the query
++ The next step in retrieving data a provider is to construct a query. This first snippet + defines some variables for accessing the User Dictionary Provider: +
+
+
+// A "projection" defines the columns that will be returned for each row
+String[] mProjection =
+{
+ UserDictionary.Words._ID, // Contract class constant for the _ID column name
+ UserDictionary.Words.WORD, // Contract class constant for the word column name
+ UserDictionary.Words.LOCALE // Contract class constant for the locale column name
+};
+
+// Defines a string to contain the selection clause
+String mSelectionClause = null;
+
+// Initializes an array to contain selection arguments
+String[] mSelectionArgs = {""};
+
+
++ The next snippet shows how to use + {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()}, using the User Dictionary Provider as an example. + A provider client query is similar to an SQL query, and it contains a set of columns to return, + a set of selection criteria, and a sort order. +
+
+ The set of columns that the query should return is called a projection
+ (the variable mProjection).
+
+ The expression that specifies the rows to retrieve is split into a selection clause and
+ selection arguments. The selection clause is a combination of logical and Boolean expressions,
+ column names, and values (the variable mSelection). If you specify the replaceable
+ parameter ? instead of a value, the query method retrieves the value from the
+ selection arguments array (the variable mSelectionArgs).
+
+ In the next snippet, if the user doesn't enter a word, the selection clause is set to
+ null, and the query returns all the words in the provider. If the user enters
+ a word, the selection clause is set to UserDictionary.Words.Word + " = ?" and
+ the first element of selection arguments array is set to the word the user enters.
+
+/*
+ * This defines a one-element String array to contain the selection argument.
+ */
+String[] mSelectionArgs = {""};
+
+// Gets a word from the UI
+mSearchString = mSearchWord.getText().toString();
+
+// Remember to insert code here to check for invalid or malicious input.
+
+// If the word is the empty string, gets everything
+if (TextUtils.isEmpty(mSearchString)) {
+ // Setting the selection clause to null will return all words
+ mSelectionClause = null;
+ mSelectionArgs[0] = "";
+
+} else {
+ // Constructs a selection clause that matches the word that the user entered.
+ mSelectionClause = " = ?";
+
+ // Moves the user's input string to the selection arguments.
+ mSelectionArgs[0] = mSearchString;
+
+}
+
+// Does a query against the table and returns a Cursor object
+mCursor = getContentResolver().query(
+ UserDictionary.Words.CONTENT_URI, // The content URI of the words table
+ mProjection, // The columns to return for each row
+ mSelectionClause // Either null, or the word the user entered
+ mSelectionArgs, // Either empty, or the string the user entered
+ mSortOrder); // The sort order for the returned rows
+
+// Some providers return null if an error occurs, others throw an exception
+if (null == mCursor) {
+ /*
+ * Insert code here to handle the error. Be sure not to use the cursor! You may want to
+ * call android.util.Log.e() to log this error.
+ *
+ */
+// If the Cursor is empty, the provider found no matches
+} else if (mCursor.getCount() < 1) {
+
+ /*
+ * Insert code here to notify the user that the search was unsuccessful. This isn't necessarily
+ * an error. You may want to offer the user the option to insert a new row, or re-type the
+ * search term.
+ */
+
+} else {
+ // Insert code here to do something with the results
+
+}
+
++ This query is analogous to the SQL statement: +
++SELECT _ID, word, frequency, locale FROM words WHERE word = <userinput> ORDER BY word ASC; ++
+ In this SQL statement, the actual column names are used instead of contract class constants. +
+Protecting against malicious input
++ If the data managed by the content provider is in an SQL database, including external untrusted + data into raw SQL statements can lead to SQL injection. +
++ Consider this selection clause: +
++// Constructs a selection clause by concatenating the user's input to the column name +String mSelectionClause = "var = " + mUserInput; ++
+ If you do this, you're allowing the user to concatenate malicious SQL onto your SQL statement.
+ For example, the user could enter "nothing; DROP TABLE *;" for mUserInput, which
+ would result in the selection clause var = nothing; DROP TABLE *;. Since the
+ selection clause is treated as an SQL statement, this might cause the provider to erase all of
+ the tables in the underlying SQLite database (unless the provider is set up to catch
+ SQL injection attempts).
+
+ To avoid this problem, use a selection clause that uses ? as a replaceable
+ parameter and a separate array of selection arguments. When you do this, the user input
+ is bound directly to the query rather than being interpreted as part of an SQL statement.
+ Because it's not treated as SQL, the user input can't inject malicious SQL. Instead of using
+ concatenation to include the user input, use this selection clause:
+
+// Constructs a selection clause with a replaceable parameter +String mSelectionClause = "var = ?"; ++
+ Set up the array of selection arguments like this: +
+
+// Defines an array to contain the selection arguments
+String[] selectionArgs = {""};
+
++ Put a value in the selection arguments array like this: +
++// Sets the selection argument to the user's input +selectionArgs[0] = mUserInput; ++
+ A selection clause that uses ? as a replaceable parameter and an array of
+ selection arguments array are preferred way to specify a selection, even the provider isn't
+ based on an SQL database.
+
Displaying query results
++ The {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()} client method always returns a {@link android.database.Cursor} + containing the columns specified by the query's projection for the rows that match the query's + selection criteria. A {@link android.database.Cursor} object provides random read access to the + rows and columns it contains. Using {@link android.database.Cursor} methods, + you can iterate over the rows in the results, determine the data type of each column, get the + data out of a column, and examine other properties of the results. Some + {@link android.database.Cursor} implementations automatically update the object when the + provider's data changes, or trigger methods in an observer object when the + {@link android.database.Cursor} changes, or both. +
++ Note: A provider may restrict access to columns based on the nature of the + object making the query. For example, the Contacts Provider restricts access for some columns to + sync adapters, so it won't return them to an activity or service. +
++ If no rows match the selection criteria, the provider + returns a {@link android.database.Cursor} object for which + {@link android.database.Cursor#getCount() Cursor.getCount()} is 0 (an empty cursor). +
+
+ If an internal error occurs, the results of the query depend on the particular provider. It may
+ choose to return null, or it may throw an {@link java.lang.Exception}.
+
+ Since a {@link android.database.Cursor} is a "list" of rows, a good way to display the + contents of a {@link android.database.Cursor} is to link it to a {@link android.widget.ListView} + via a {@link android.widget.SimpleCursorAdapter}. +
++ The following snippet continues the code from the previous snippet. It creates a + {@link android.widget.SimpleCursorAdapter} object containing the {@link android.database.Cursor} + retrieved by the query, and sets this object to be the adapter for a + {@link android.widget.ListView}: +
+
+// Defines a list of columns to retrieve from the Cursor and load into an output row
+String[] mWordListColumns =
+{
+ UserDictionary.Words.WORD, // Contract class constant containing the word column name
+ UserDictionary.Words.LOCALE // Contract class constant containing the locale column name
+};
+
+// Defines a list of View IDs that will receive the Cursor columns for each row
+int[] mWordListItems = { R.id.dictWord, R.id.locale};
+
+// Creates a new SimpleCursorAdapter
+mCursorAdapter = new SimpleCursorAdapter(
+ getApplicationContext(), // The application's Context object
+ R.layout.wordlistrow, // A layout in XML for one row in the ListView
+ mCursor, // The result from the query
+ mWordListColumns, // A string array of column names in the cursor
+ mWordListItems, // An integer array of view IDs in the row layout
+ 0); // Flags (usually none are needed)
+
+// Sets the adapter for the ListView
+mWordList.setAdapter(mCursorAdapter);
+
+
+ Note: To back a {@link android.widget.ListView} with a
+ {@link android.database.Cursor}, the cursor must contain a column named _ID.
+ Because of this, the query shown previously retrieves the _ID column for the
+ "words" table, even though the {@link android.widget.ListView} doesn't display it.
+ This restriction also explains why most providers have a _ID column for each of
+ their tables.
+
Getting data from query results
++ Rather than simply displaying query results, you can use them for other tasks. For + example, you can retrieve spellings from the user dictionary and then look them up in + other providers. To do this, you iterate over the rows in the {@link android.database.Cursor}: +
+
+
+// Determine the column index of the column named "word"
+int index = mCursor.getColumnIndex(UserDictionary.Words.WORD);
+
+/*
+ * Only executes if the cursor is valid. The User Dictionary Provider returns null if
+ * an internal error occurs. Other providers may throw an Exception instead of returning null.
+ */
+
+if (mCursor != null) {
+ /*
+ * Moves to the next row in the cursor. Before the first movement in the cursor, the
+ * "row pointer" is -1, and if you try to retrieve data at that position you will get an
+ * exception.
+ */
+ while (mCursor.moveToNext()) {
+
+ // Gets the value from the column.
+ newWord = mCursor.getString(index);
+
+ // Insert code here to process the retrieved word.
+
+ ...
+
+ // end of while loop
+ }
+} else {
+
+ // Insert code here to report an error if the cursor is null or the provider threw an exception.
+}
+
++ {@link android.database.Cursor} implementations contain several "get" methods for + retrieving different types of data from the object. For example, the previous snippet + uses {@link android.database.Cursor#getString(int) getString()}. They also have a + {@link android.database.Cursor#getType(int) getType()} method that returns a value indicating + the data type of the column. +
+ + + +Content Provider Permissions
++ A provider's application can specify permissions that other applications must have in order to + access the provider's data. These permissions ensure that the user knows what data + an application will try to access. Based on the provider's requirements, other applications + request the permissions they need in order to access the provider. End users see the requested + permissions when they install the application. +
++ If a provider's application doesn't specify any permissions, then other applications have no + access to the provider's data. However, components in the provider's application always have + full read and write access, regardless of the specified permissions. +
+
+ As noted previously, the User Dictionary Provider requires the
+ android.permission.READ_USER_DICTIONARY permission to retrieve data from it.
+ The provider has the separate android.permission.WRITE_USER_DICTIONARY
+ permission for inserting, updating, or deleting data.
+
+ To get the permissions needed to access a provider, an application requests them with a
+
+ <uses-permission> element in its manifest file.
+ When the Android Package Manager installs the application, a user must approve all of the
+ permissions the application requests. If the user approves all of them, Package Manager
+ continues the installation; if the user doesn't approve them, Package Manager
+ aborts the installation.
+
+ The following
+
+ <uses-permission> element requests read access to the User Dictionary Provider:
+
+ <uses-permission android:name="android.permission.READ_USER_DICTIONARY"> ++
+ The impact of permissions on provider access is explained in more detail in the + Security and Permissions guide. +
+ + + +Inserting, Updating, and Deleting Data
++ In the same way that you retrieve data from a provider, you also use the interaction between + a provider client and the provider's {@link android.content.ContentProvider} to modify data. + You call a method of {@link android.content.ContentResolver} with arguments that are passed to + the corresponding method of {@link android.content.ContentProvider}. The provider and provider + client automatically handle security and inter-process communication. +
+Inserting data
++ To insert data into a provider, you call the + {@link android.content.ContentResolver#insert(Uri,ContentValues) ContentResolver.insert()} + method. This method inserts a new row into the provider and returns a content URI for that row. + This snippet shows how to insert a new word into the User Dictionary Provider: +
++// Defines a new Uri object that receives the result of the insertion +Uri mNewUri; + +... + +// Defines an object to contain the new values to insert +ContentValues mNewValues = new ContentValues(); + +/* + * Sets the values of each column and inserts the word. The arguments to the "put" + * method are "column name" and "value" + */ +mNewValues.put(UserDictionary.Words.APP_ID, "example.user"); +mNewValues.put(UserDictionary.Words.LOCALE, "en_US"); +mNewValues.put(UserDictionary.Words.WORD, "insert"); +mNewValues.put(UserDictionary.Words.FREQUENCY, "100"); + +mNewUri = getContentResolver().insert( + UserDictionary.Word.CONTENT_URI, // the user dictionary content URI + mNewValues // the values to insert +); ++
+ The data for the new row goes into a single {@link android.content.ContentValues} object, which
+ is similar in form to a one-row cursor. The columns in this object don't need to have the
+ same data type, and if you don't want to specify a value at all, you can set a column
+ to null using {@link android.content.ContentValues#putNull(String)
+ ContentValues.putNull()}.
+
+ The snippet doesn't add the _ID column, because this column is maintained
+ automatically. The provider assigns a unique value of _ID to every row that is
+ added. Providers usually use this value as the table's primary key.
+
+ The content URI returned in newUri identifies the newly-added row, with
+ the following format:
+
+content://user_dictionary/words/<id_value> ++
+ The <id_value> is the contents of _ID for the new row.
+ Most providers can detect this form of content URI automatically and then perform the requested
+ operation on that particular row.
+
+ To get the value of _ID from the returned {@link android.net.Uri}, call
+ {@link android.content.ContentUris#parseId(Uri) ContentUris.parseId()}.
+
Updating data
+
+ To update a row, you use a {@link android.content.ContentValues} object with the updated
+ values just as you do with an insertion, and selection criteria just as you do with a query.
+ The client method you use is
+ {@link android.content.ContentResolver#update(Uri, ContentValues, String, String[])
+ ContentResolver.update()}. You only need to add values to the
+ {@link android.content.ContentValues} object for columns you're updating. If you want to clear
+ the contents of a column, set the value to null.
+
+ The following snippet changes all the rows whose locale has the language "en" to a
+ have a locale of null. The return value is the number of rows that were updated:
+
+// Defines an object to contain the updated values
+ContentValues mUpdateValues = new ContentValues();
+
+// Defines selection criteria for the rows you want to update
+String mSelectionClause = UserDictionary.Words.LOCALE + "LIKE ?";
+String[] mSelectionArgs = {"en_%"};
+
+// Defines a variable to contain the number of updated rows
+int mRowsUpdated = 0;
+
+...
+
+/*
+ * Sets the updated value and updates the selected words.
+ */
+mUpdateValues.putNull(UserDictionary.Words.LOCALE);
+
+mRowsUpdated = getContentResolver().update(
+ UserDictionary.Words.CONTENT_URI, // the user dictionary content URI
+ mUpdateValues // the columns to update
+ mSelectionClause // the column to select on
+ mSelectionArgs // the value to compare to
+);
+
++ You should also sanitize user input when you call + {@link android.content.ContentResolver#update(Uri, ContentValues, String, String[]) + ContentResolver.update()}. To learn more about this, read the section + Protecting against malicious input. +
+Deleting data
++ Deleting rows is similar to retrieving row data: you specify selection criteria for the rows + you want to delete and the client method returns the number of deleted rows. + The following snippet deletes rows whose appid matches "user". The method returns the + number of deleted rows. +
+
+
+// Defines selection criteria for the rows you want to delete
+String mSelectionClause = UserDictionary.Words.APP_ID + " LIKE ?";
+String[] mSelectionArgs = {"user"};
+
+// Defines a variable to contain the number of rows deleted
+int mRowsDeleted = 0;
+
+...
+
+// Deletes the words that match the selection criteria
+mRowsDeleted = getContentResolver().delete(
+ UserDictionary.Words.CONTENT_URI, // the user dictionary content URI
+ mSelectionClause // the column to select on
+ mSelectionArgs // the value to compare to
+);
+
++ You should also sanitize user input when you call + {@link android.content.ContentResolver#delete(Uri, String, String[]) + ContentResolver.delete()}. To learn more about this, read the section + Protecting against malicious input. +
+ +Provider Data Types
++ Content providers can offer many different data types. The User Dictionary Provider offers only + text, but providers can also offer the following formats: +
+-
+
- + integer + +
- + long integer (long) + +
- + floating point + +
- + long floating point (double) + +
+ Another data type that providers often use is Binary Large OBject (BLOB) implemented as a + 64KB byte array. You can see the available data types by looking at the + {@link android.database.Cursor} class "get" methods. +
++ The data type for each column in a provider is usually listed in its documentation. + The data types for the User Dictionary Provider are listed in the reference documentation + for its contract class {@link android.provider.UserDictionary.Words} (contract classes are + described in the section Contract Classes). + You can also determine the data type by calling {@link android.database.Cursor#getType(int) + Cursor.getType()}. +
++ Providers also maintain MIME data type information for each content URI they define. You can + use the MIME type information to find out if your application can handle data that the + provider offers, or to choose a type of handling based on the MIME type. You usually need the + MIME type when you are working with a provider that contains complex + data structures or files. For example, the {@link android.provider.ContactsContract.Data} + table in the Contacts Provider uses MIME types to label the type of contact data stored in each + row. To get the MIME type corresponding to a content URI, call + {@link android.content.ContentResolver#getType(Uri) ContentResolver.getType()}. +
++ The section MIME Type Reference describes the + syntax of both standard and custom MIME types. +
+ + + +Alternative Forms of Provider Access
++ Three alternative forms of provider access are important in application development: +
+-
+
- + Batch access: You can create a batch of access calls with methods in + the {@link android.content.ContentProviderOperation} class, and then apply them with + {@link android.content.ContentResolver#applyBatch(String, ArrayList) + ContentResolver.applyBatch()}. + +
- + Asynchronous queries: You should do queries in a separate thread. One way to do this is to + use a {@link android.content.CursorLoader} object. The examples in the + Loaders guide demonstrate + how to do this. + +
- + Data access via intents: Although you can't send an intent + directly to a provider, you can send an intent to the provider's application, which is + usually the best-equipped to modify the provider's data. + +
+ Batch access and modification via intents are described in the following sections. +
+Batch access
++ Batch access to a provider is useful for inserting a large number of rows, or for inserting + rows in multiple tables in the same method call, or in general for performing a set of + operations across process boundaries as a transaction (an atomic operation). +
++ To access a provider in "batch mode", + you create an array of {@link android.content.ContentProviderOperation} objects and then + dispatch them to a content provider with + {@link android.content.ContentResolver#applyBatch(String, ArrayList) + ContentResolver.applyBatch()}. You pass the content provider's authority to this + method, rather than a particular content URI, which allows each + {@link android.content.ContentProviderOperation} object in the array to work against a + different table. A call to {@link android.content.ContentResolver#applyBatch(String, ArrayList) + ContentResolver.applyBatch()} returns an array of results. +
+
+ The description of the {@link android.provider.ContactsContract.RawContacts} contract class
+ includes a code snippet that demonstrates batch insertion. The
+ Contact Manager
+ sample application contains an example of batch access in its ContactAdder.java
+ source file.
+
Displaying data using a helper app
++ If your application does have access permissions, you still may want to use an + intent to display data in another application. For example, the Calendar application accepts an + {@link android.content.Intent#ACTION_VIEW} intent, which displays a particular date or event. + This allows you to display calendar information without having to create your own UI. + To learn more about this feature, see the + Calendar Provider guide. +
++ The application to which you send the intent doesn't have to be the application + associated with the provider. For example, you can retrieve a contact from the + Contact Provider, then send an {@link android.content.Intent#ACTION_VIEW} intent + containing the content URI for the contact's image to an image viewer. +
+Data access via intents
++ Intents can provide indirect access to a content provider. You allow the user to access + data in a provider even if your application doesn't have access permissions, either by + getting a result intent back from an application that has permissions, or by activating an + application that has permissions and letting the user do work in it. +
+Getting access with temporary permissions
++ You can access data in a content provider, even if you don't have the proper access + permissions, by sending an intent to an application that does have the permissions and + receiving back a result intent containing "URI" permissions. + These are permissions for a specific content URI that last until the activity that receives + them is finished. The application that has permanent permissions grants temporary + permissions by setting a flag in the result intent: +
+-
+
- + Read permission: + {@link android.content.Intent#FLAG_GRANT_READ_URI_PERMISSION} + +
- + Write permission: + {@link android.content.Intent#FLAG_GRANT_WRITE_URI_PERMISSION} + +
+ Note: These flags don't give general read or write access to the provider + whose authority is contained in the content URI. The access is only for the URI itself. +
+
+ A provider defines URI permissions for content URIs in its manifest, using the
+
+ android:grantUriPermission
+ attribute of the
+ {@code <provider>}
+ element, as well as the
+ {@code
+ <grant-uri-permission>} child element of the
+ {@code <provider>}
+ element. The URI permissions mechanism is explained in more detail in the
+ Security and Permissions guide,
+ in the section "URI Permissions".
+
+ For example, you can retrieve data for a contact in the Contacts Provider, even if you don't + have the {@link android.Manifest.permission#READ_CONTACTS} permission. You might want to do + this in an application that sends e-greetings to a contact on his or her birthday. Instead of + requesting {@link android.Manifest.permission#READ_CONTACTS}, which gives you access to all of + the user's contacts and all of their information, you prefer to let the user control which + contacts are used by your application. To do this, you use the following process: +
+-
+
- + Your application sends an intent containing the action + {@link android.content.Intent#ACTION_PICK} and the "contacts" MIME type + {@link android.provider.ContactsContract.RawContacts#CONTENT_ITEM_TYPE}, using the + method {@link android.app.Activity#startActivityForResult(Intent, int) + startActivityForResult()}. + +
- + Because this intent matches the intent filter for the + People app's "selection" activity, the activity will come to the foreground. + +
- + In the selection activity, the user selects a + contact to update. When this happens, the selection activity calls + {@link android.app.Activity#setResult(int, Intent) setResult(resultcode, intent)} + to set up a intent to give back to your application. The intent contains the content URI + of the contact the user selected, and the "extras" flags + {@link android.content.Intent#FLAG_GRANT_READ_URI_PERMISSION}. These flags grant URI + permission to your app to read data for the contact pointed to by the + content URI. The selection activity then calls {@link android.app.Activity#finish()} to + return control to your application. + +
- + Your activity returns to the foreground, and the system calls your activity's + {@link android.app.Activity#onActivityResult(int, int, Intent) onActivityResult()} + method. This method receives the result intent created by the selection activity in + the People app. + +
- + With the content URI from the result intent, you can read the contact's data + from the Contacts Provider, even though you didn't request permanent read access permission + to the provider in your manifest. You can then get the contact's birthday information + or his or her email address and then send the e-greeting. + +
Using another application
++ A simple way to allow the user to modify data to which you don't have access permissions is to + activate an application that has permissions and let the user do the work there. +
++ For example, the Calendar application accepts an + {@link android.content.Intent#ACTION_INSERT} intent, which allows you to activate the + application's insert UI. You can pass "extras" data in this intent, which the application + uses to pre-populate the UI. Because recurring events have a complex syntax, the preferred + way of inserting events into the Calendar Provider is to activate the Calendar app with an + {@link android.content.Intent#ACTION_INSERT} and then let the user insert the event there. +
+ +Contract Classes
++ A contract class defines constants that help applications work with the content URIs, column + names, intent actions, and other features of a content provider. Contract classes are not + included automatically with a provider; the provider's developer has to define them and then + make them available to other developers. Many of the providers included with the Android + platform have corresponding contract classes in the package {@link android.provider}. +
++ For example, the User Dictionary Provider has a contract class + {@link android.provider.UserDictionary} containing content URI and column name constants. The + content URI for the "words" table is defined in the constant + {@link android.provider.UserDictionary.Words#CONTENT_URI UserDictionary.Words.CONTENT_URI}. + The {@link android.provider.UserDictionary.Words} class also contains column name constants, + which are used in the example snippets in this guide. For example, a query projection can be + defined as: +
+
+String[] mProjection =
+{
+ UserDictionary.Words._ID,
+ UserDictionary.Words.WORD,
+ UserDictionary.Words.LOCALE
+};
+
++ Another contract class is {@link android.provider.ContactsContract} for the Contacts Provider. + The reference documentation for this class includes example code snippets. One of its + subclasses, {@link android.provider.ContactsContract.Intents.Insert}, is a contract + class that contains constants for intents and intent data. +
+ + + +MIME Type Reference
++ Content providers can return standard MIME media types, or custom MIME type strings, or both. +
++ MIME types have the format +
++type/subtype ++
+ For example, the well-known MIME type text/html has the text type and
+ the html subtype. If the provider returns this type for a URI, it means that a
+ query using that URI will return text containing HTML tags.
+
+ Custom MIME type strings, also called "vendor-specific" MIME types, have more + complex type and subtype values. The type value is always +
++vnd.android.cursor.dir ++
+ for multiple rows, or +
++vnd.android.cursor.item ++
+ for a single row. +
++ The subtype is provider-specific. The Android built-in providers usually have a simple + subtype. For example, the when the Contacts application creates a row for a telephone number, + it sets the following MIME type in the row: +
++vnd.android.cursor.item/phone_v2 ++
+ Notice that the subtype value is simply phone_v2.
+
+ Other provider developers may create their own pattern of subtypes based on the provider's
+ authority and table names. For example, consider a provider that contains train timetables.
+ The provider's authority is com.example.trains, and it contains the tables
+ Line1, Line2, and Line3. In response to the content URI
+
+
+content://com.example.trains/Line1 ++
+ for table Line1, the provider returns the MIME type +
++vnd.android.cursor.dir/vnd.example.line1 ++
+ In response to the content URI +
++content://com.example.trains/Line2/5 ++
+ for row 5 in table Line2, the provider returns the MIME type +
++vnd.android.cursor.item/vnd.example.line2 ++
+ Most content providers define contract class constants for the MIME types they use. The + Contacts Provider contract class {@link android.provider.ContactsContract.RawContacts}, + for example, defines the constant + {@link android.provider.ContactsContract.RawContacts#CONTENT_ITEM_TYPE} for the MIME type of + a single raw contact row. +
++ Content URIs for single rows are described in the section + Content URIs. +
diff --git a/docs/html/guide/topics/providers/content-provider-creating.jd b/docs/html/guide/topics/providers/content-provider-creating.jd new file mode 100644 index 0000000000000..4ebdb502138ce --- /dev/null +++ b/docs/html/guide/topics/providers/content-provider-creating.jd @@ -0,0 +1,1215 @@ +page.title=Creating a Content Provider +@jd:body +In this document
+-
+
- + Designing Data Storage + +
- + Designing Content URIs + +
- + Implementing the ContentProvider Class + + +
-
+ Implementing Content Provider MIME Types
+
-
+
- + MIME types for tables + +
- + MIME types for files + +
+ - + Implementing a Contract Class + +
- + Implementing Content Provider Permissions + +
- + The <provider> Element + +
- + Intents and Data Access + +
Key classes
+-
+
- + {@link android.content.ContentProvider} + +
- + {@link android.database.Cursor} + +
- + {@link android.net.Uri} + +
Related Samples
+-
+
- + + Note Pad sample application + + +
See also
+-
+
- + + Content Provider Basics + +
- + + Calendar Provider + +
+ A content provider manages access to a central repository of data. You implement a + provider as one or more classes in an Android application, along with elements in + the manifest file. One of your classes implements a subclass + {@link android.content.ContentProvider}, which is the interface between your provider and + other applications. Although content providers are meant to make data available to other + applications, you may of course have activities in your application that allow the user + to query and modify the data managed by your provider. +
++ The rest of this topic is a basic list of steps for building a content provider and a list + of APIs to use. +
+ + + +Before You Start Building
++ Before you start building a provider, do the following: +
+-
+
-
+ Decide if you need a content provider. You need to build a content
+ provider if you want to provide one or more of the following features:
+
-
+
- You want to offer complex data or files to other applications. +
- You want to allow users to copy complex data from your app into other apps. +
- You want to provide custom search suggestions using the search framework. +
+ You don't need a provider to use an SQLite database if the use is entirely within + your own application. +
+
+ - + If you haven't done so already, read the topic + + Content Provider Basics to learn more about providers. + +
+ Next, follow these steps to build your provider: +
+-
+
-
+ Design the raw storage for your data. A content provider offers data in two ways:
+
-
+
- + File data + +
- + Data that normally goes into files, such as + photos, audio, or videos. Store the files in your application's private + space. In response to a request for a file from another application, your + provider can offer a handle to the file. + +
- + "Structured" data + +
- + Data that normally goes into a database, array, or similar structure. + Store the data in a form that's compatible with tables of rows and columns. A row + represents an entity, such as a person or an item in inventory. A column represents + some data for the entity, such a person's name or an item's price. A common way to + store this type of data is in an SQLite database, but you can use any type of + persistent storage. To learn more about the storage types available in the + Android system, see the section + Designing Data Storage. + +
+ - + Define a concrete implementation of the {@link android.content.ContentProvider} class and + its required methods. This class is the interface between your data and the rest of the + Android system. For more information about this class, see the section + Implementing the ContentProvider Class. + +
- + Define the provider's authority string, its content URIs, and column names. If you want + the provider's application to handle intents, also define intent actions, extras data, + and flags. Also define the permissions that you will require for applications that want + to access your data. You should consider defining all of these values as constants in a + separate contract class; later, you can expose this class to other developers. For more + information about content URIs, see the + section Designing Content URIs. + For more information about intents, see the + section Intents and Data Access. + +
- + Add other optional pieces, such as sample data or an implementation + of {@link android.content.AbstractThreadedSyncAdapter} that can synchronize data between + the provider and cloud-based data. + +
Designing Data Storage
++ A content provider is the interface to data saved in a structured format. Before you create + the interface, you must decide how to store the data. You can store the data in any form you + like, and then design the interface to read and write the data as necessary. +
++ These are some of the data storage technologies that are available in Android: +
+-
+
-
+ The Android system includes an SQLite database API that Android's own providers use
+ to store table-oriented data. The
+ {@link android.database.sqlite.SQLiteOpenHelper} class helps you create databases, and the
+ {@link android.database.sqlite.SQLiteDatabase} class is the base class for accessing
+ databases.
+
+ Remember that you don't have to use a database to implement your repository. A provider + appears externally as a set of tables, similar to a relational database, but this is + not a requirement for the provider's internal implementation. +
+
+ - + For storing file data, Android has a variety of file-oriented APIs. + To learn more about file storage, read the topic + Data Storage. If you're + designing a provider that offers media-related data such as music or videos, you can + have a provider that combines table data and files. + +
- + For working with network-based data, use classes in {@link java.net} and + {@link android.net}. You can also synchronize network-based data to a local data + store such as a database, and then offer the data as tables or files. + The + Sample Sync Adapter sample application demonstrates this type of synchronization. + +
+ Data design considerations +
++ Here are some tips for designing your provider's data structure: +
+-
+
-
+ Table data should always have a "primary key" column that the provider maintains
+ as a unique numeric value for each row. You can use this value to link the row to related
+ rows in other tables (using it as a "foreign key"). Although you can use any name
+ for this column, using {@link android.provider.BaseColumns#_ID BaseColumns._ID} is the best
+ choice, because linking the results of a provider query to a
+ {@link android.widget.ListView} requires one of the retrieved columns to have the name
+
_ID. +
+ - + If you want to provide bitmap images or other very large pieces of file-oriented data, store + the data in a file and then provide it indirectly rather than storing it directly in a + table. If you do this, you need to tell users of your provider that they need to use a + {@link android.content.ContentResolver} file method to access the data. + +
-
+ Use the Binary Large OBject (BLOB) data type to store data that varies in size or has a
+ varying structure. For example, you can use a BLOB column to store a
+ protocol buffer or
+ JSON structure.
+
+ You can also use a BLOB to implement a schema-independent table. In + this type of table, you define a primary key column, a MIME type column, and one or + more generic columns as BLOB. The meaning of the data in the BLOB columns is indicated + by the value in the MIME type column. This allows you to store different row types in + the same table. The Contacts Provider's "data" table + {@link android.provider.ContactsContract.Data} is an example of a schema-independent + table. +
+
+
Designing Content URIs
++ A content URI is a URI that identifies data in a provider. Content URIs include + the symbolic name of the entire provider (its authority) and a + name that points to a table or file (a path). The optional id part points to + an individual row in a table. Every data access method of + {@link android.content.ContentProvider} has a content URI as an argument; this allows you to + determine the table, row, or file to access. +
++ The basics of content URIs are described in the topic + + Content Provider Basics. +
+Designing an authority
+
+ A provider usually has a single authority, which serves as its Android-internal name. To
+ avoid conflicts with other providers, you should use Internet domain ownership (in reverse)
+ as the basis of your provider authority. Because this recommendation is also true for Android
+ package names, you can define your provider authority as an extension of the name
+ of the package containing the provider. For example, if your Android package name is
+ com.example.<appname>, you should give your provider the
+ authority com.example.<appname>.provider.
+
Designing a path structure
+
+ Developers usually create content URIs from the authority by appending paths that point to
+ individual tables. For example, if you have two tables table1 and
+ table2, you combine the authority from the previous example to yield the
+ content URIs
+ com.example.<appname>.provider/table1 and
+ com.example.<appname>.provider/table2. Paths aren't
+ limited to a single segment, and there doesn't have to be a table for each level of the path.
+
Handling content URI IDs
+
+ By convention, providers offer access to a single row in a table by accepting a content URI
+ with an ID value for the row at the end of the URI. Also by convention, providers match the
+ ID value to the table's _ID column, and perform the requested access against the
+ row that matches.
+
+ This convention facilitates a common design pattern for apps accessing a provider. The app
+ does a query against the provider and displays the resulting {@link android.database.Cursor}
+ in a {@link android.widget.ListView} using a {@link android.widget.CursorAdapter}.
+ The definition of {@link android.widget.CursorAdapter} requires one of the columns in the
+ {@link android.database.Cursor} to be _ID
+
+ The user then picks one of the displayed rows from the UI in order to look at or modify the
+ data. The app gets the corresponding row from the {@link android.database.Cursor} backing the
+ {@link android.widget.ListView}, gets the _ID value for this row, appends it to
+ the content URI, and sends the access request to the provider. The provider can then do the
+ query or modification against the exact row the user picked.
+
Content URI patterns
+
+ To help you choose which action to take for an incoming content URI, the provider API includes
+ the convenience class {@link android.content.UriMatcher}, which maps content URI "patterns" to
+ integer values. You can use the integer values in a switch statement that
+ chooses the desired action for the content URI or URIs that match a particular pattern.
+
+ A content URI pattern matches content URIs using wildcard characters: +
+-
+
-
+
*: Matches a string of any valid characters of any length. +
+ -
+
#: Matches a string of numeric characters of any length. +
+
+ As an example of designing and coding content URI handling, consider a provider with the
+ authority com.example.app.provider that recognizes the following content URIs
+ pointing to tables:
+
-
+
-
+
content://com.example.app.provider/table1: A table calledtable1. +
+ -
+
content://com.example.app.provider/table2/dataset1: A table called +dataset1. +
+ -
+
content://com.example.app.provider/table2/dataset2: A table called +dataset2. +
+ -
+
content://com.example.app.provider/table3: A table calledtable3. +
+
+ The provider also recognizes these content URIs if they have a row ID appended to them, as
+ for example content://com.example.app.provider/table3/1 for the row identified by
+ 1 in table3.
+
+ The following content URI patterns would be possible: +
+-
+
-
+
content://com.example.app.provider/*+
+ - + Matches any content URI in the provider. + +
-
+
content://com.example.app.provider/table2/*: +
+ -
+ Matches a content URI for the tables
dataset1+ anddataset2, but doesn't match content URIs fortable1or +table3. +
+ -
+
content://com.example.app.provider/table3/#: Matches a content URI + for single rows intable3, such as +content://com.example.app.provider/table3/6for the row identified by +6. +
+
+ The following code snippet shows how the methods in {@link android.content.UriMatcher} work.
+ This code handles URIs for an entire table differently from URIs for a
+ single row, by using the content URI pattern
+ content://<authority>/<path> for tables, and
+ content://<authority>/<path>/<id> for single rows.
+
+ The method {@link android.content.UriMatcher#addURI(String, String, int) addURI()} maps an
+ authority and path to an integer value. The method android.content.UriMatcher#match(Uri)
+ match()} returns the integer value for a URI. A switch statement
+ chooses between querying the entire table, and querying for a single record:
+
+public class ExampleProvider extends ContentProvider {
+...
+ // Creates a UriMatcher object.
+ private static final UriMatcher sUriMatcher;
+...
+ /*
+ * The calls to addURI() go here, for all of the content URI patterns that the provider
+ * should recognize. For this snippet, only the calls for table 3 are shown.
+ */
+...
+ /*
+ * Sets the integer value for multiple rows in table 3 to 1. Notice that no wildcard is used
+ * in the path
+ */
+ sUriMatcher.addURI("com.example.app.provider", "table3", 1);
+
+ /*
+ * Sets the code for a single row to 2. In this case, the "#" wildcard is
+ * used. "content://com.example.app.provider/table3/3" matches, but
+ * "content://com.example.app.provider/table3 doesn't.
+ */
+ sUriMatcher.addURI("com.example.app.provider", "table3/#", 2);
+...
+ // Implements ContentProvider.query()
+ public Cursor query(
+ Uri uri,
+ String[] projection,
+ String selection,
+ String[] selectionArgs,
+ String sortOrder) {
+...
+ /*
+ * Choose the table to query and a sort order based on the code returned for the incoming
+ * URI. Here, too, only the statements for table 3 are shown.
+ */
+ switch (sUriMatcher.match(uri)) {
+
+
+ // If the incoming URI was for all of table3
+ case 1:
+
+ if (TextUtils.isEmpty(sortOrder)) sortOrder = "_ID ASC";
+ break;
+
+ // If the incoming URI was for a single row
+ case 2:
+
+ /*
+ * Because this URI was for a single row, the _ID value part is
+ * present. Get the last path segment from the URI; this is the _ID value.
+ * Then, append the value to the WHERE clause for the query
+ */
+ selection = selection + "_ID = " uri.getLastPathSegment();
+ break;
+
+ default:
+ ...
+ // If the URI is not recognized, you should do some error handling here.
+ }
+ // call the code to actually do the query
+ }
+
+
+ Another class, {@link android.content.ContentUris}, provides convenience methods for working
+ with the id part of content URIs. The classes {@link android.net.Uri} and
+ {@link android.net.Uri.Builder} include convenience methods for parsing existing
+ {@link android.net.Uri} objects and building new ones.
+
Implementing the ContentProvider Class
++ The {@link android.content.ContentProvider} instance manages access + to a structured set of data by handling requests from other applications. All forms + of access eventually call {@link android.content.ContentResolver}, which then calls a concrete + method of {@link android.content.ContentProvider} to get access. +
+Required methods
++ The abstract class {@link android.content.ContentProvider} defines six abstract methods that + you must implement as part of your own concrete subclass. All of these methods except + {@link android.content.ContentProvider#onCreate() onCreate()} are called by a client application + that is attempting to access your content provider: +
+-
+
- + {@link android.content.ContentProvider#query(Uri, String[], String, String[], String) + query()} + +
- + Retrieve data from your provider. Use the arguments to select the table to + query, the rows and columns to return, and the sort order of the result. + Return the data as a {@link android.database.Cursor} object. + +
- + {@link android.content.ContentProvider#insert(Uri, ContentValues) insert()} + +
- + Insert a new row into your provider. Use the arguments to select the + destination table and to get the column values to use. Return a content URI for the + newly-inserted row. + +
- + {@link android.content.ContentProvider#update(Uri, ContentValues, String, String[]) + update()} + +
- + Update existing rows in your provider. Use the arguments to select the table and rows + to update and to get the updated column values. Return the number of rows updated. + +
- + {@link android.content.ContentProvider#delete(Uri, String, String[]) delete()} + +
- + Delete rows from your provider. Use the arguments to select the table and the rows to + delete. Return the number of rows deleted. + +
- + {@link android.content.ContentProvider#getType(Uri) getType()} + +
- + Return the MIME type corresponding to a content URI. This method is described in more + detail in the section Implementing Content Provider MIME Types. + +
- + {@link android.content.ContentProvider#onCreate() onCreate()} + +
- + Initialize your provider. The Android system calls this method immediately after it + creates your provider. Notice that your provider is not created until a + {@link android.content.ContentResolver} object tries to access it. + +
+ Notice that these methods have the same signature as the identically-named + {@link android.content.ContentResolver} methods. +
++ Your implementation of these methods should account for the following: +
+-
+
- + All of these methods except {@link android.content.ContentProvider#onCreate() onCreate()} + can be called by multiple threads at once, so they must be thread-safe. To learn + more about multiple threads, see the topic + + Processes and Threads. + +
- + Avoid doing lengthy operations in {@link android.content.ContentProvider#onCreate() + onCreate()}. Defer initialization tasks until they are actually needed. + The section Implementing the onCreate() method + discusses this in more detail. + +
- + Although you must implement these methods, your code does not have to do anything except + return the expected data type. For example, you may want to prevent other applications + from inserting data into some tables. To do this, you can ignore the call to + {@link android.content.ContentProvider#insert(Uri, ContentValues) insert()} and return + 0. + +
Implementing the query() method
+
+ The
+ {@link android.content.ContentProvider#query(Uri, String[], String, String[], String)
+ ContentProvider.query()} method must return a {@link android.database.Cursor} object, or if it
+ fails, throw an {@link java.lang.Exception}. If you are using an SQLite database as your data
+ storage, you can simply return the {@link android.database.Cursor} returned by one of the
+ query() methods of the {@link android.database.sqlite.SQLiteDatabase} class.
+ If the query does not match any rows, you should return a {@link android.database.Cursor}
+ instance whose {@link android.database.Cursor#getCount()} method returns 0.
+ You should return null only if an internal error occurred during the query process.
+
+ If you aren't using an SQLite database as your data storage, use one of the concrete subclasses + of {@link android.database.Cursor}. For example, the {@link android.database.MatrixCursor} class + implements a cursor in which each row is an array of {@link java.lang.Object}. With this class, + use {@link android.database.MatrixCursor#addRow(Object[]) addRow()} to add a new row. +
++ Remember that the Android system must be able to communicate the {@link java.lang.Exception} + across process boundaries. Android can do this for the following exceptions that may be useful + in handling query errors: +
+-
+
- + {@link java.lang.IllegalArgumentException} (You may choose to throw this if your provider + receives an invalid content URI) + +
- + {@link java.lang.NullPointerException} + +
Implementing the insert() method
++ The {@link android.content.ContentProvider#insert(Uri, ContentValues) insert()} method adds a + new row to the appropriate table, using the values in the {@link android.content.ContentValues} + argument. If a column name is not in the {@link android.content.ContentValues} argument, you + may want to provide a default value for it either in your provider code or in your database + schema. +
+
+ This method should return the content URI for the new row. To construct this, append the new
+ row's _ID (or other primary key) value to the table's content URI, using
+ {@link android.content.ContentUris#withAppendedId(Uri, long) withAppendedId()}.
+
Implementing the delete() method
++ The {@link android.content.ContentProvider#delete(Uri, String, String[]) delete()} method + does not have to physically delete rows from your data storage. If you are using a sync adapter + with your provider, you should consider marking a deleted row + with a "delete" flag rather than removing the row entirely. The sync adapter can + check for deleted rows and remove them from the server before deleting them from the provider. +
+Implementing the update() method
+
+ The {@link android.content.ContentProvider#update(Uri, ContentValues, String, String[])
+ update()} method takes the same {@link android.content.ContentValues} argument used by
+ {@link android.content.ContentProvider#insert(Uri, ContentValues) insert()}, and the
+ same selection and selectionArgs arguments used by
+ {@link android.content.ContentProvider#delete(Uri, String, String[]) delete()} and
+ {@link android.content.ContentProvider#query(Uri, String[], String, String[], String)
+ ContentProvider.query()}. This may allow you to re-use code between these methods.
+
Implementing the onCreate() method
++ The Android system calls {@link android.content.ContentProvider#onCreate() + onCreate()} when it starts up the provider. You should perform only fast-running initialization + tasks in this method, and defer database creation and data loading until the provider actually + receives a request for the data. If you do lengthy tasks in + {@link android.content.ContentProvider#onCreate() onCreate()}, you will slow down your + provider's startup. In turn, this will slow down the response from the provider to other + applications. +
++ For example, if you are using an SQLite database you can create + a new {@link android.database.sqlite.SQLiteOpenHelper} object in + {@link android.content.ContentProvider#onCreate() ContentProvider.onCreate()}, + and then create the SQL tables the first time you open the database. To facilitate this, the + first time you call {@link android.database.sqlite.SQLiteOpenHelper#getWritableDatabase + getWritableDatabase()}, it automatically calls the + {@link android.database.sqlite.SQLiteOpenHelper#onCreate(SQLiteDatabase) + SQLiteOpenHelper.onCreate()} method. +
++ The following two snippets demonstrate the interaction between + {@link android.content.ContentProvider#onCreate() ContentProvider.onCreate()} and + {@link android.database.sqlite.SQLiteOpenHelper#onCreate(SQLiteDatabase) + SQLiteOpenHelper.onCreate()}. The first snippet is the implementation of + {@link android.content.ContentProvider#onCreate() ContentProvider.onCreate()}: +
+
+public class ExampleProvider extends ContentProvider
+
+ /*
+ * Defines a handle to the database helper object. The MainDatabaseHelper class is defined
+ * in a following snippet.
+ */
+ private MainDatabaseHelper mOpenHelper;
+
+ // Defines the database name
+ private static final String DBNAME = "mydb";
+
+ // Holds the database object
+ private SQLiteDatabase db;
+
+ public boolean onCreate() {
+
+ /*
+ * Creates a new helper object. This method always returns quickly.
+ * Notice that the database itself isn't created or opened
+ * until SQLiteOpenHelper.getWritableDatabase is called
+ */
+ mOpenHelper = new SQLiteOpenHelper(
+ getContext(), // the application context
+ DBNAME, // the name of the database)
+ null, // uses the default SQLite cursor
+ 1 // the version number
+ );
+
+ return true;
+ }
+
+ ...
+
+ // Implements the provider's insert method
+ public Cursor insert(Uri uri, ContentValues values) {
+ // Insert code here to determine which table to open, handle error-checking, and so forth
+
+ ...
+
+ /*
+ * Gets a writeable database. This will trigger its creation if it doesn't already exist.
+ *
+ */
+ db = mOpenHelper.getWritableDatabase();
+ }
+}
+
++ The next snippet is the implementation of + {@link android.database.sqlite.SQLiteOpenHelper#onCreate(SQLiteDatabase) + SQLiteOpenHelper.onCreate()}, including a helper class: +
+
+...
+// A string that defines the SQL statement for creating a table
+private static final String SQL_CREATE_MAIN = "CREATE TABLE " +
+ "main " + // Table's name
+ "(" + // The columns in the table
+ " _ID INTEGER PRIMARY KEY, " +
+ " WORD TEXT"
+ " FREQUENCY INTEGER " +
+ " LOCALE TEXT )";
+...
+/**
+ * Helper class that actually creates and manages the provider's underlying data repository.
+ */
+protected static final class MainDatabaseHelper extends SQLiteOpenHelper {
+
+ /*
+ * Instantiates an open helper for the provider's SQLite data repository
+ * Do not do database creation and upgrade here.
+ */
+ MainDatabaseHelper(Context context) {
+ super(context, DBNAME, null, 1);
+ }
+
+ /*
+ * Creates the data repository. This is called when the provider attempts to open the
+ * repository and SQLite reports that it doesn't exist.
+ */
+ public void onCreate(SQLiteDatabase db) {
+
+ // Creates the main table
+ db.execSQL(SQL_CREATE_MAIN);
+ }
+}
+
+
+
+
+Implementing ContentProvider MIME Types
++ The {@link android.content.ContentProvider} class has two methods for returning MIME types: +
+-
+
- + {@link android.content.ContentProvider#getType(Uri) getType()} + +
- + One of the required methods that you must implement for any provider. + +
- + {@link android.content.ContentProvider#getStreamTypes(Uri, String) getStreamTypes()} + +
- + A method that you're expected to implement if your provider offers files. + +
MIME types for tables
++ The {@link android.content.ContentProvider#getType(Uri) getType()} method returns a + {@link java.lang.String} in MIME format that describes the type of data returned by the content + URI argument. The {@link android.net.Uri} argument can be a pattern rather than a specific URI; + in this case, you should return the type of data associated with content URIs that match the + pattern. +
++ For common types of data such as as text, HTML, or JPEG, + {@link android.content.ContentProvider#getType(Uri) getType()} should return the standard + MIME type for that data. A full list of these standard types is available on the + IANA MIME Media Types + website. +
++ For content URIs that point to a row or rows of table data, + {@link android.content.ContentProvider#getType(Uri) getType()} should return + a MIME type in Android's vendor-specific MIME format: +
+-
+
-
+ Type part:
vnd+
+ -
+ Subtype part:
+
-
+
-
+ If the URI pattern is for a single row:
android.cursor.item/+
+ -
+ If the URI pattern is for more than one row:
android.cursor.dir/+
+
+ -
+ If the URI pattern is for a single row:
-
+ Provider-specific part:
vnd.<name>.<type>++ You supply the
+ +<name>and<type>. + The<name>value should be globally unique, + and the<type>value should be unique to the corresponding URI + pattern. A good choice for<name>is your company's name or + some part of your application's Android package name. A good choice for the +<type>is a string that identifies the table associated with the + URI. +
+
+ For example, if a provider's authority is
+ com.example.app.provider, and it exposes a table named
+ table1, the MIME type for multiple rows in table1 is:
+
+vnd.android.cursor.dir/vnd.com.example.provider.table1 ++
+ For a single row of table1, the MIME type is:
+
+vnd.android.cursor.item/vnd.com.example.provider.table1 ++
MIME types for files
++ If your provider offers files, implement + {@link android.content.ContentProvider#getStreamTypes(Uri, String) getStreamTypes()}. + The method returns a {@link java.lang.String} array of MIME types for the files your provider + can return for a given content URI. You should filter the MIME types you offer by the MIME type + filter argument, so that you return only those MIME types that the client wants to handle. +
+
+ For example, consider a provider that offers photo images as files in .jpg,
+ .png, and .gif format.
+ If an application calls {@link android.content.ContentResolver#getStreamTypes(Uri, String)
+ ContentResolver.getStreamTypes()} with the filter string image/* (something that
+ is an "image"),
+ then the {@link android.content.ContentProvider#getStreamTypes(Uri, String)
+ ContentProvider.getStreamTypes()} method should return the array:
+
+{ "image/jpeg", "image/png", "image/gif"}
+
+
+ If the app is only interested in .jpg files, then it can call
+ {@link android.content.ContentResolver#getStreamTypes(Uri, String)
+ ContentResolver.getStreamTypes()} with the filter string *\/jpeg, and
+ {@link android.content.ContentProvider#getStreamTypes(Uri, String)
+ ContentProvider.getStreamTypes()} should return:
+
+{"image/jpeg"}
+
+
+ If your provider doesn't offer any of the MIME types requested in the filter string,
+ {@link android.content.ContentProvider#getStreamTypes(Uri, String) getStreamTypes()}
+ should return null.
+
Implementing a Contract Class
+
+ A contract class is a public final class that contains constant definitions for the
+ URIs, column names, MIME types, and other meta-data that pertain to the provider. The class
+ establishes a contract between the provider and other applications by ensuring that the provider
+ can be correctly accessed even if there are changes to the actual values of URIs, column names,
+ and so forth.
+
+ A contract class also helps developers because it usually has mnemonic names for its constants, + so developers are less likely to use incorrect values for column names or URIs. Since it's a + class, it can contain Javadoc documentation. Integrated development environments such as + Eclipse can auto-complete constant names from the contract class and display Javadoc for the + constants. +
+
+ Developers can't access the contract class's class file from your application, but they can
+ statically compile it into their application from a .jar file you provide.
+
+ The {@link android.provider.ContactsContract} class and its nested classes are examples of + contract classes. +
+Implementing Content Provider Permissions
++ Permissions and access for all aspects of the Android system are described in detail in the + topic Security and Permissions. + The topic Data Storage also + described the security and permissions in effect for various types of storage. + In brief, the important points are: +
+-
+
- + By default, data files stored on the device's internal storage are private to your + application and provider. + +
- + {@link android.database.sqlite.SQLiteDatabase} databases you create are private to your + application and provider. + +
- + By default, data files that you save to external storage are public and + world-readable. You can't use a content provider to restrict access to files in + external storage, because other applications can use other API calls to read and write them. + +
- + The method calls for opening or creating files or SQLite databases on your device's internal + storage can potentially give both read and write access to all other applications. If you + use an internal file or database as your provider's repository, and you give it + "world-readable" or "world-writeable" access, the permissions you set for your provider in + its manifest won't protect your data. The default access for files and databases in + internal storage is "private", and for your provider's repository you shouldn't change this. + +
+ If you want to use content provider permissions to control access to your data, then you should + store your data in internal files, SQLite databases, or the "cloud" (for example, + on a remote server), and you should keep files and databases private to your application. +
+Implementing permissions
+
+ All applications can read from or write to your provider, even if the underlying data is
+ private, because by default your provider does not have permissions set. To change this,
+ set permissions for your provider in your manifest file, using attributes or child
+ elements of the
+ <provider> element. You can set permissions that apply to the entire provider,
+ or to certain tables, or even to certain records, or all three.
+
+ You define permissions for your provider with one or more
+
+ <permission> elements in your manifest file. To make the
+ permission unique to your provider, use Java-style scoping for the
+
+ android:name attribute. For example, name the read permission
+ com.example.app.provider.permission.READ_PROVIDER.
+
+
+ The following list describes the scope of provider permissions, starting with the + permissions that apply to the entire provider and then becoming more fine-grained. + More fine-grained permissions take precedence over ones with larger scope: +
+-
+
- + Single read-write provider-level permission + +
-
+ One permission that controls both read and write access to the entire provider, specified
+ with the
+ android:permissionattribute of the ++ <provider>element. +
+ - + Separate read and write provider-level permission + +
-
+ A read permission and a write permission for the entire provider. You specify them
+ with the
+ android:readPermissionand ++ android:writePermissionattributes of the ++ <provider>element. They take precedence over the permission required by ++ android:permission. +
+ - + Path-level permission + +
-
+ Read, write, or read/write permission for a content URI in your provider. You specify
+ each URI you want to control with a
+
+ <path-permission>child element of the ++ <provider>element. For each content URI you specify, you can specify a + read/write permission, a read permission, or a write permission, or all three. The read and + write permissions take precedence over the read/write permission. Also, path-level + permission takes precedence over provider-level permissions. +
+ - + Temporary permission + +
-
+ A permission level that grants temporary access to an application, even if the application
+ doesn't have the permissions that are normally required. The temporary
+ access feature reduces the number of permissions an application has to request in
+ its manifest. When you turn on temporary permissions, the only applications that need
+ "permanent" permissions for your provider are ones that continually access all
+ your data.
+
+ Consider the permissions you need to implement an email provider and app, when you + want to allow an outside image viewer application to display photo attachments from your + provider. To give the image viewer the necessary access without requiring permissions, + set up temporary permissions for content URIs for photos. Design your email app so + that when the user wants to display a photo, the app sends an intent containing the + photo's content URI and permission flags to the image viewer. The image viewer can + then query your email provider to retrieve the photo, even though the viewer doesn't + have the normal read permission for your provider. +
++ To turn on temporary permissions, either set the +
++ android:grantUriPermissionsattribute of the ++ <provider>element, or add one or more ++ <grant-uri-permission>child elements to your ++ <provider>element. If you use temporary permissions, you have to call + {@link android.content.Context#revokeUriPermission(Uri, int) + Context.revokeUriPermission()} whenever you remove support for a content URI from your + provider, and the content URI is associated with a temporary permission. ++ The attribute's value determines how much of your provider is made accessible. + If the attribute is set to
+true, then the system will grant temporary + permission to your entire provider, overriding any other permissions that are required + by your provider-level or path-level permissions. ++ If this flag is set to
+false, then you must add ++ <grant-uri-permission>child elements to your ++ <provider>element. Each child element specifies the content URI or + URIs for which temporary access is granted. ++ To delegate temporary access to an application, an intent must contain + the {@link android.content.Intent#FLAG_GRANT_READ_URI_PERMISSION} or the + {@link android.content.Intent#FLAG_GRANT_WRITE_URI_PERMISSION} flags, or both. These + are set with the {@link android.content.Intent#setFlags(int) setFlags()} method. +
++ If the
++ android:grantUriPermissionsattribute is not present, it's assumed to be +false. +
+
The <provider> Element
+
+ Like {@link android.app.Activity} and {@link android.app.Service} components,
+ a subclass of {@link android.content.ContentProvider}
+ must be defined in the manifest file for its application, using the
+
+ <provider> element. The Android system gets the following information from
+ the element:
+
-
+
- + Authority + ({@code + android:authorities}) + +
- + Symbolic names that identify the entire provider within the system. This + attribute is described in more detail in the section + Designing Content URIs. + +
-
+ Provider class name
+ (
+android:name +) +
+ - + The class that implements {@link android.content.ContentProvider}. This class is + described in more detail in the section + Implementing the ContentProvider Class. + +
- + Permissions + +
-
+ Attributes that specify the permissions that other applications must have in order to access
+ the provider's data:
+
-
+
-
+
+ android:grantUriPermssions: Temporary permission flag. +
+ -
+
+ android:permission: Single provider-wide read/write permission. +
+ -
+
+ android:readPermission: Provider-wide read permission. +
+ -
+
+ android:writePermission: Provider-wide write permission. +
+
+ Permissions and their corresponding attributes are described in more + detail in the section + Implementing Content Provider Permissions. +
+
+ -
+
- + Startup and control attributes + +
-
+ These attributes determine how and when the Android system starts the provider, the
+ process characteristics of the provider, and other run-time settings:
+
-
+
-
+
+ android:enabled: Flag allowing the system to start the provider. +
+ -
+
+ android:exported: Flag allowing other applications to use this provider. +
+ -
+
+ android:initOrder: The order in which this provider should be started, + relative to other providers in the same process. +
+ -
+
+ android:multiProcess: Flag allowing the system to start the provider + in the same process as the calling client. +
+ -
+
+ android:process: The name of the process in which the provider should + run. +
+ -
+
+ android:syncable: Flag indicating that the provider's data is to be + sync'ed with data on a server. +
+
+ The attributes are fully documented in the dev guide topic for the +
++ <provider>+ element. +
+ -
+
- + Informational attributes + +
-
+ An optional icon and label for the provider:
+
-
+
-
+
+ android:icon: A drawable resource containing an icon for the provider. + The icon appears next to the provider's label in the list of apps in + Settings > Apps > All. +
+ -
+
+ android:label: An informational label describing the provider or its + data, or both. The label appears in the list of apps in + Settings > Apps > All. +
+
+ The attributes are fully documented in the dev guide topic for the +
++ <provider>element. +
+ -
+
Intents and Data Access
++ Applications can access a content provider indirectly with an {@link android.content.Intent}. + The application does not call any of the methods of {@link android.content.ContentResolver} or + {@link android.content.ContentProvider}. Instead, it sends an intent that starts an activity, + which is often part of the provider's own application. The destination activity is in charge of + retrieving and displaying the data in its UI. Depending on the action in the intent, the + destination activity may also prompt the user to make modifications to the provider's data. + An intent may also contain "extras" data that the destination activity displays + in the UI; the user then has the option of changing this data before using it to modify the + data in the provider. +
++ +
++ You may want to use intent access to help ensure data integrity. Your provider may depend + on having data inserted, updated, and deleted according to strictly defined business logic. If + this is the case, allowing other applications to directly modify your data may lead to + invalid data. If you want developers to use intent access, be sure to document it thoroughly. + Explain to them why intent access using your own application's UI is better than trying to + modify the data with their code. +
++ Handling an incoming intent that wishes to modify your provider's data is no different from + handling other intents. You can learn more about using intents by reading the topic + Intents and Intent Filters. +
diff --git a/docs/html/guide/topics/providers/content-providers.jd b/docs/html/guide/topics/providers/content-providers.jd index 95331ce38519e..1707f038b3ce0 100644 --- a/docs/html/guide/topics/providers/content-providers.jd +++ b/docs/html/guide/topics/providers/content-providers.jd @@ -1,922 +1,96 @@ page.title=Content Providers @jd:body -In this document
+ + +Topics
-
-
- Content provider basics -
- Querying a content provider -
- Modifying data in a provider -
- Creating a content provider -
- Content URI summary +
- + + Content Provider Basics + +
- + + Creating a Content Provider + +
- + Calendar Provider +
Key classes
--
-
- {@link android.content.ContentProvider} -
- {@link android.content.ContentResolver} -
- {@link android.database.Cursor} -
See also
- + +Related Samples
+-
+
- + + Contact Manager application + +
- + + "Cursor (People)" + + +
- + + "Cursor (Phones)" + +
-Content providers store and retrieve data and make it accessible to all -applications. They're the only way to share data across applications; there's -no common storage area that all Android packages can access. -
- --Android ships with a number of content providers for common data types -(audio, video, images, personal contact information, and so on). You can -see some of them listed in the {@link android.provider android.provider} -package. You can query these providers for the data they contain (although, -for some, you must acquire the proper permission to read the data). -
- -Note: Android 4.0 introduces the Calendar -Provider. For more information, see Calendar -Provider.
--If you want to make your own data public, you have two options: You can -create your own content provider (a {@link android.content.ContentProvider} -subclass) or you can add the data to an existing provider — if there's -one that controls the same type of data and you have permission to write to it. -
- --This document is an introduction to using content providers. After a -brief discussion of the fundamentals, it explores how to query a content -provider, how to modify data controlled by a provider, and how to create -a content provider of your own. -
- - -Content Provider Basics
- --How a content provider actually stores its data under the covers is -up to its designer. But all content providers implement a common interface -for querying the provider and returning results — as well as for -adding, altering, and deleting data. -
- -
-It's an interface that clients use indirectly, most generally through
-{@link android.content.ContentResolver} objects. You get a ContentResolver
-by calling {@link android.content.Context#getContentResolver
-getContentResolver()} from within the implementation of an Activity
-or other application component:
-
ContentResolver cr = getContentResolver();- -
-You can then use the ContentResolver's methods to interact with whatever -content providers you're interested in. -
- --When a query is initiated, the Android system identifies the content provider -that's the target of the query and makes sure that it is up and running. -The system instantiates all ContentProvider objects; you never need to do it -on your own. In fact, you never deal directly with ContentProvider objects -at all. Typically, there's just a single instance of each type of -ContentProvider. But it can communicate with multiple ContentResolver objects -in different applications and processes. The interaction between processes is -handled by the ContentResolver and ContentProvider classes. -
- - -The data model
- --Content providers expose their data as a simple table on a database model, -where each row is a record and each column is data of a particular type -and meaning. For example, information about people and their phone numbers -might be exposed as follows: -
- -| _ID | -NUMBER | -NUMBER_KEY | -LABEL | -NAME | -TYPE | -
|---|---|---|---|---|---|
| 13 | -(425) 555 6677 | -425 555 6677 | -Kirkland office | -Bully Pulpit | -{@code TYPE_WORK} | -
| 44 | -(212) 555-1234 | -212 555 1234 | -NY apartment | -Alan Vain | -{@code TYPE_HOME} | -
| 45 | -(212) 555-6657 | -212 555 6657 | -Downtown office | -Alan Vain | -{@code TYPE_MOBILE} | -
| 53 | -201.555.4433 | -201 555 4433 | -Love Nest | -Rex Cars | -{@code TYPE_HOME} | -
-Every record includes a numeric {@code _ID} field that uniquely identifies -the record within the table. IDs can be used to match records in related -tables — for example, to find a person's phone number in one table -and pictures of that person in another. -
- --A query returns a {@link android.database.Cursor} object that can move from -record to record and column to column to read the contents of each field. -It has specialized methods for reading each type of data. So, to read a field, -you must know what type of data the field contains. (There's more on query -results and Cursor objects later.) -
- - -URIs
- --Each content provider exposes a public URI (wrapped as a {@link android.net.Uri} -object) that uniquely identifies its data set. A content provider that controls -multiple data sets (multiple tables) exposes a separate URI for each one. All -URIs for providers begin with the string "{@code content://}". The {@code content:} -scheme identifies the data as being controlled by a content provider. -
- --If you're defining a content provider, it's a good idea to also define a -constant for its URI, to simplify client code and make future updates cleaner. -Android defines {@code CONTENT_URI} constants for all the providers that come -with the platform. For example, the URI for the table that matches -phone numbers to people and the URI for the table that holds pictures of -people (both controlled by the Contacts content provider) are: -
- --
{@code android.provider.Contacts.Phones.CONTENT_URI}
-
{@code android.provider.Contacts.Photos.CONTENT_URI}
+ Content providers manage access to a structured set of data. They encapsulate the
+ data, and provide mechanisms for defining data security. Content providers are the standard
+ interface that connects data in one process with code running in another process.
-The URI constant is used in all interactions with the content provider. -Every {@link android.content.ContentResolver} method takes the URI -as its first argument. It's what identifies which provider the ContentResolver -should talk to and which table of the provider is being targeted. -
- - -Querying a Content Provider
- --You need three pieces of information to query a content provider: -
- --
-
- The URI that identifies the provider -
- The names of the data fields you want to receive -
- The data types for those fields -
-If you're querying a particular record, you also need the ID for that record. -
- - -Making the query
- -
-To query a content provider, you can use either the
-{@link android.content.ContentResolver#query ContentResolver.query()}
-method or the {@link android.app.Activity#managedQuery
-Activity.managedQuery()} method.
-Both methods take the same set of arguments, and both return a
-Cursor object. However, {@code managedQuery()}
-causes the activity to manage the life cycle of the Cursor. A managed Cursor
-handles all of the niceties, such as unloading itself when the activity pauses,
-and requerying itself when the activity restarts. You can ask an Activity to
-begin managing an unmanaged Cursor object for you by calling
-{@link android.app.Activity#startManagingCursor
-Activity.startManagingCursor()}.
-
-The first argument to either {@link android.content.ContentResolver#query query()}
-or {@link android.app.Activity#managedQuery managedQuery()} is the provider URI
-— the {@code CONTENT_URI} constant that identifies a particular
-ContentProvider and data set (see URIs earlier).
-
-To restrict a query to just one record, you can append the {@code _ID} value for -that record to the URI — that is, place a string matching the ID as the -last segment of the path part of the URI. For example, if the ID is 23, -the URI would be: -
- -{@code content://. . . ./23}
- -
-There are some helper methods, particularly
-{@link android.content.ContentUris#withAppendedId
-ContentUris.withAppendedId()} and {@link
-android.net.Uri#withAppendedPath Uri.withAppendedPath()},
-that make it easy to append an ID to a URI. Both are static methods that return
-a Uri object with the ID added. So, for example, if you were looking for record
-23 in the database of people contacts, you might construct a query as follows:
-
-import android.provider.Contacts.People; -import android.content.ContentUris; -import android.net.Uri; -import android.database.Cursor; - -// Use the ContentUris method to produce the base URI for the contact with _ID == 23. -Uri myPerson = ContentUris.withAppendedId(People.CONTENT_URI, 23); - -// Alternatively, use the Uri method to produce the base URI. -// It takes a string rather than an integer. -Uri myPerson = Uri.withAppendedPath(People.CONTENT_URI, "23"); - -// Then query for this specific record: -Cursor cur = managedQuery(myPerson, null, null, null, null); -- -
-The other arguments to the {@link android.content.ContentResolver#query query()}
-and {@link android.app.Activity#managedQuery managedQuery()} methods delimit
-the query in more detail. They are:
-
-
-
- The names of the data columns that should be returned. A {@code null} -value returns all columns. Otherwise, only columns that are listed by name -are returned. All the content providers that come with the platform define -constants for their columns. For example, the -{@link android.provider.Contacts.Phones android.provider.Contacts.Phones} class -defines constants for the names of the columns in the phone table illustrated -earlier — {@code _ID}, {@code NUMBER}, {@code NUMBER_KEY}, {@code NAME}, -and so on. - -
A filter detailing which rows to return, formatted as an SQL {@code WHERE} -clause (excluding the {@code WHERE} itself). A {@code null} value returns -all rows (unless the URI limits the query to a single record).
-
-Selection arguments.
-
-A sorting order for the rows that are returned, formatted as an SQL -{@code ORDER BY} clause (excluding the {@code ORDER BY} itself). A {@code null} -value returns the records in the default order for the table, which may be -unordered.
-
-Let's look at an example query to retrieve a list of contact names and their -primary phone numbers: + When you want to access data in a content provider, you use the + {@link android.content.ContentResolver} object in your + application's {@link android.content.Context} to communicate with the provider as a client. + The {@link android.content.ContentResolver} object communicates with the provider object, an + instance of a class that implements {@link android.content.ContentProvider}. The provider + object receives data requests from clients, performs the requested action, and + returns the results.
- -
-import android.provider.Contacts.People;
-import android.database.Cursor;
-
-// Form an array specifying which columns to return.
-String[] projection = new String[] {
- People._ID,
- People._COUNT,
- People.NAME,
- People.NUMBER
- };
-
-// Get the base URI for the People table in the Contacts content provider.
-Uri contacts = People.CONTENT_URI;
-
-// Make the query.
-Cursor managedCursor = managedQuery(contacts,
- projection, // Which columns to return
- null, // Which rows to return (all rows)
- null, // Selection arguments (none)
- // Put the results in ascending order by name
- People.NAME + " ASC");
-
-
-This query retrieves data from the People table of the Contacts content -provider. It gets the name, primary phone number, and unique record ID for -each contact. It also reports the number of records that are returned as -the {@code _COUNT} field of each record. + You don't need to develop your own provider if you don't intend to share your data with + other applications. However, you do need your own provider to provide custom search + suggestions in your own application. You also need your own provider if you want to copy and + paste complex data or files from your application to other applications.
-
-The constants for the names of the columns are defined in various interfaces
-— {@code _ID} and {@code _COUNT} in
-{@link android.provider.BaseColumns BaseColumns}, {@code NAME} in {@link android.provider.Contacts.PeopleColumns PeopleColumns}, and {@code NUMBER}
-in {@link android.provider.Contacts.PhonesColumns PhoneColumns}. The
-{@link android.provider.Contacts.People Contacts.People} class implements
-each of these interfaces, which is why the code example above could refer
-to them using just the class name.
+ Android itself includes content providers that manage data such as audio, video, images, and
+ personal contact information. You can see some of them listed in the reference
+ documentation for the
+ android.provider
+ package. With some restrictions, these providers are accessible to any Android
+ application.
+
+ The following topics describe content providers in more detail:
- - -What a query returns
- --A query returns a set of zero or more database records. The names of the -columns, their default order, and their data types are specific to each -content provider. -But every provider has an {@code _ID} column, which holds a unique numeric -ID for each record. Every provider can also report the number -of records returned as the {@code _COUNT} column; its value -is the same for all rows. -
- --Here is an example result set for the query in the previous section: -
- -| _ID | -_COUNT | -NAME | -NUMBER | -
|---|---|---|---|
| 44 | -3 | -Alan Vain | -212 555 1234 | -
| 13 | -3 | -Bully Pulpit | -425 555 6677 | -
| 53 | -3 | -Rex Cars | -201 555 4433 | -
-The retrieved data is exposed by a {@link android.database.Cursor Cursor} -object that can be used to iterate backward or forward through the result -set. You can use this object only to read the data. To add, modify, or -delete data, you must use a ContentResolver object. -
- - -Reading retrieved data
- -
-The Cursor object returned by a query provides access to a recordset of
-results. If you have queried for a specific record by ID, this set will
-contain only one value. Otherwise, it can contain multiple values.
-(If there are no matches, it can also be empty.) You
-can read data from specific fields in the record, but you must know the
-data type of the field, because the Cursor object has a separate method
-for reading each type of data — such as {@link
-android.database.Cursor#getString getString()}, {@link
-android.database.Cursor#getInt getInt()}, and {@link
-android.database.Cursor#getFloat getFloat()}.
-(However, for most types, if you call the method for reading strings,
-the Cursor object will give you the String representation of the data.)
-The Cursor lets you request the column name from the index of the column,
-or the index number from the column name.
-
-The following snippet demonstrates reading names and phone numbers from -the query illustrated earlier: -
- -
-import android.provider.Contacts.People;
-
-private void getColumnData(Cursor cur){
- if (cur.moveToFirst()) {
-
- String name;
- String phoneNumber;
- int nameColumn = cur.getColumnIndex(People.NAME);
- int phoneColumn = cur.getColumnIndex(People.NUMBER);
- String imagePath;
-
- do {
- // Get the field values
- name = cur.getString(nameColumn);
- phoneNumber = cur.getString(phoneColumn);
-
- // Do something with the values.
- ...
-
- } while (cur.moveToNext());
-
- }
-}
-
-
-
-If a query can return binary data, such as an image or sound, the data
-may be directly entered in the table or the table entry for that data may be
-a string specifying a {@code content:} URI that you can use to get the data.
-In general, smaller amounts of data (say, from 20 to 50K or less) are most often
-directly entered in the table and can be read by calling
-{@link android.database.Cursor#getBlob Cursor.getBlob()}.
-It returns a byte array.
-
-If the table entry is a {@code content:} URI, you should never try to open
-and read the file directly (for one thing, permissions problems can make this
-fail). Instead, you should call
-{@link android.content.ContentResolver#openInputStream
-ContentResolver.openInputStream()} to get an
-{@link java.io.InputStream} object that you can use to read the data.
-
Modifying Data
- --Data kept by a content provider can be modified by: -
- --
-
- Adding new records -
- Adding new values to existing records -
- Batch updating existing records -
- Deleting records -
-All data modification is accomplished using {@link android.content.ContentResolver} -methods. Some content providers require a more restrictive permission for writing -data than they do for reading it. If you don't have permission to write to a -content provider, the ContentResolver methods will fail. -
- - -Adding records
- -
-To add a new record to a content provider, first set up a map of key-value pairs
-in a {@link android.content.ContentValues} object, where each key matches
-the name of a column in the content provider and the value is the desired
-value for the new record in that column. Then call {@link
-android.content.ContentResolver#insert ContentResolver.insert()} and pass
-it the URI of the provider and the ContentValues map. This method returns
-the full URI of the new record — that is, the provider's URI with
-the appended ID for the new record. You can then use this URI to query and
-get a Cursor over the new record, and to further modify the record.
-Here's an example:
-
-import android.provider.Contacts.People; -import android.content.ContentResolver; -import android.content.ContentValues; - -ContentValues values = new ContentValues(); - -// Add Abraham Lincoln to contacts and make him a favorite. -values.put(People.NAME, "Abraham Lincoln"); -// 1 = the new contact is added to favorites -// 0 = the new contact is not added to favorites -values.put(People.STARRED, 1); - -Uri uri = getContentResolver().insert(People.CONTENT_URI, values); -- - -
Adding new values
- --Once a record exists, you can add new information to it or modify -existing information. For example, the next step in the example above would -be to add contact information — like a phone number or an IM or e-mail -address — to the new entry. -
- --The best way to add to a record in the Contacts database is to append -the name of the table where the new data goes to the URI for the -record, then use the amended URI to add the new data values. Each -Contacts table exposes a name for this purpose as a {@code -CONTENT_DIRECTORY} constant. The following code continues the previous -example by adding a phone number and e-mail address for the record -just created: -
- --Uri phoneUri = null; -Uri emailUri = null; - -// Add a phone number for Abraham Lincoln. Begin with the URI for -// the new record just returned by insert(); it ends with the _ID -// of the new record, so we don't have to add the ID ourselves. -// Then append the designation for the phone table to this URI, -// and use the resulting URI to insert the phone number. -phoneUri = Uri.withAppendedPath(uri, People.Phones.CONTENT_DIRECTORY); - -values.clear(); -values.put(People.Phones.TYPE, People.Phones.TYPE_MOBILE); -values.put(People.Phones.NUMBER, "1233214567"); -getContentResolver().insert(phoneUri, values); - -// Now add an email address in the same way. -emailUri = Uri.withAppendedPath(uri, People.ContactMethods.CONTENT_DIRECTORY); - -values.clear(); -// ContactMethods.KIND is used to distinguish different kinds of -// contact methods, such as email, IM, etc. -values.put(People.ContactMethods.KIND, Contacts.KIND_EMAIL); -values.put(People.ContactMethods.DATA, "test@example.com"); -values.put(People.ContactMethods.TYPE, People.ContactMethods.TYPE_HOME); -getContentResolver().insert(emailUri, values); -- -
-You can place small amounts of binary data into a table by calling
-the version of {@link android.content.ContentValues#put
-ContentValues.put()} that takes a byte array.
-That would work for a small icon-like image or a short audio clip, for example.
-However, if you have a large amount of binary data to add, such as a photograph
-or a complete song, put a {@code content:} URI for the data in the table and call
-{@link android.content.ContentResolver#openOutputStream
-ContentResolver.openOutputStream()}
-with the file's URI. (That causes the content provider to store the data
-in a file and record the file path in a hidden field of the record.)
-
-In this regard, the {@link android.provider.MediaStore} content -provider, the main provider that dispenses image, audio, and video -data, employs a special convention: The same URI that is used with -{@code query()} or {@code managedQuery()} to get meta-information -about the binary data (such as, the caption of a photograph or the -date it was taken) is used with {@code openInputStream()} -to get the data itself. Similarly, the same URI that is used with -{@code insert()} to put meta-information into a MediaStore record -is used with {@code openOutputStream()} to place the binary data there. -The following code snippet illustrates this convention: -
- -
-import android.provider.MediaStore.Images.Media;
-import android.content.ContentValues;
-import java.io.OutputStream;
-
-// Save the name and description of an image in a ContentValues map.
-ContentValues values = new ContentValues(3);
-values.put(Media.DISPLAY_NAME, "road_trip_1");
-values.put(Media.DESCRIPTION, "Day 1, trip to Los Angeles");
-values.put(Media.MIME_TYPE, "image/jpeg");
-
-// Add a new record without the bitmap, but with the values just set.
-// insert() returns the URI of the new record.
-Uri uri = getContentResolver().insert(Media.EXTERNAL_CONTENT_URI, values);
-
-// Now get a handle to the file for that record, and save the data into it.
-// Here, sourceBitmap is a Bitmap object representing the file to save to the database.
-try {
- OutputStream outStream = getContentResolver().openOutputStream(uri);
- sourceBitmap.compress(Bitmap.CompressFormat.JPEG, 50, outStream);
- outStream.close();
-} catch (Exception e) {
- Log.e(TAG, "exception while writing image", e);
-}
-
-
-
-Batch updating records
- -
-To batch update a group of records (for example, to change "NY" to "New York"
-in all fields), call the {@link
-android.content.ContentResolver#update ContentResolver.update()}
-method with the columns and values to change.
-
Deleting a record
- -
-To delete a single record, call {{@link
-android.content.ContentResolver#delete ContentResolver.delete()}
-with the URI of a specific row.
-
-To delete multiple rows, call {@link
-android.content.ContentResolver#delete ContentResolver.delete()}
-with the URI of the type of record to delete (for example, {@code android.provider.Contacts.People.CONTENT_URI}) and an SQL {@code WHERE}
-clause defining which rows to delete. (Caution:
-Be sure to include a valid {@code WHERE} clause if you're deleting a general
-type, or you risk deleting more records than you intended!).
-
Creating a Content Provider
- --To create a content provider, you must: -
- --
-
- Set up a system for storing the data. Most content providers -store their data using Android's file storage methods or SQLite databases, -but you can store your data any way you want. Android provides the -{@link android.database.sqlite.SQLiteOpenHelper SQLiteOpenHelper} -class to help you create a database and {@link -android.database.sqlite.SQLiteDatabase SQLiteDatabase} to manage it. - -
Extend the {@link android.content.ContentProvider} class to provide -access to the data.
-
-Declare the content provider in the manifest file for your -application (AndroidManifest.xml).
-
-The following sections have notes on the last two of these tasks. -
- - -Extending the ContentProvider class
- --You define a {@link android.content.ContentProvider} subclass to -expose your data to others using the conventions expected by -ContentResolver and Cursor objects. Principally, this means -implementing six abstract methods declared in the ContentProvider class: -
- -{@code query()}
-
{@code insert()}
-
{@code update()}
-
{@code delete()}
-
{@code getType()}
-
{@code onCreate()}
-The {@code query()} method must return a {@link android.database.Cursor} object -that can iterate over the requested data. Cursor itself is an interface, but -Android provides some ready-made Cursor objects that you can use. For example, -{@link android.database.sqlite.SQLiteCursor} can iterate over data stored in -an SQLite database. You get the Cursor object by calling any of the {@link -android.database.sqlite.SQLiteDatabase SQLiteDatabase} class's {@code query()} -methods. There are other Cursor implementations — such as {@link -android.database.MatrixCursor} — for data not stored in a database. -
- --Because these ContentProvider methods can be called from -various ContentResolver objects in different processes and threads, -they must be implemented in a thread-safe manner. -
- -
-As a courtesy, you might also want to call {@link android.content.ContentResolver#notifyChange(android.net.Uri,android.database.ContentObserver)
-ContentResolver.notifyChange()} to notify listeners when there are
-modifications to the data.
-
-Beyond defining the subclass itself, there are other steps you should take -to simplify the work of clients and make the class more accessible: -
- --
-
- Define a {@code public static final} {@link android.net.Uri}
-named {@code CONTENT_URI}. This is the string that represents the full
-{@code content:} URI that your content provider handles. You must define a
-unique string for this value. The best solution is to use the fully-qualified
-class name of the content provider (made lowercase). So, for example, the
-URI for a TransportationProvider class could be defined as follows:
-
-
public static final Uri CONTENT_URI = - Uri.parse("content://com.example.codelab.transportationprovider");- --If the provider has subtables, also define {@code CONTENT_URI} constants for -each of the subtables. These URIs should all have the same authority (since -that identifies the content provider), and be distinguished only by their paths. -For example: -
- -{@code content://com.example.codelab.transportationprovider/train} -
- -
{@code content://com.example.codelab.transportationprovider/air/domestic} -
{@code content://com.example.codelab.transportationprovider/air/international}-For an overview of {@code content:} URIs, see the Content URI -Summary at the end of this document. -
-
- Define the column names that the content provider will return to clients. -If you are using an underlying database, these column names are typically -identical to the SQL database column names they represent. Also define -{@code public static} String constants that clients can use to specify -the columns in queries and other instructions. -
- --Be sure to include an integer column named "{@code _id}" -(with the constant {@code _ID}) for -the IDs of the records. You should have this field whether or not you have -another field (such as a URL) that is also unique among all records. If -you're using the SQLite database, the {@code _ID} field should be the -following type: -
- -{@code INTEGER PRIMARY KEY AUTOINCREMENT}
- --The {@code AUTOINCREMENT} descriptor is optional. But without it, SQLite -increments an ID counter field to the next number above the largest -existing number in the column. If you delete the last row, the next row added -will have the same ID as the deleted row. {@code AUTOINCREMENT} avoids this -by having SQLite increment to the next largest value whether deleted or not. -
-
-
-Carefully document the data type of each column. Clients need this -information to read the data.
-
-If you are handling a new data type, you must define a new MIME type -to return in your implementation of
{@link -android.content.ContentProvider#getType ContentProvider.getType()}. -The type depends in part on whether or not the {@code content:} URI submitted -to {@code getType()} limits the request to a specific record. There's one -form of the MIME type for a single record and another for multiple records. -Use the {@link android.net.Uri Uri} methods to help determine what is being -requested. Here is the general format for each type:
-
-For a single record: {@code vnd.android.cursor.item/vnd.yourcompanyname.contenttype}
- -For example, a request for train record 122, like this URI,
-{@code content://com.example.transportationprovider/trains/122}
- -might return this MIME type:
-{@code vnd.android.cursor.item/vnd.example.rail}
-
-
-For multiple records: {@code vnd.android.cursor.dir/vnd.yourcompanyname.contenttype}
- -For example, a request for all train records, like the following URI,
-{@code content://com.example.transportationprovider/trains}
- -might return this MIME type:
-{@code vnd.android.cursor.dir/vnd.example.rail}
-
-If you are exposing byte data that's too big to put in the table itself -— such as a large bitmap file — the field that exposes the -data to clients should actually contain a {@code content:} URI string. -This is the field that gives clients access to the data file. The record -should also have another field, named "{@code _data}" that lists the exact file -path on the device for that file. This field is not intended to be read by -the client, but by the ContentResolver. The client will call
{@link -android.content.ContentResolver#openInputStream ContentResolver.openInputStream()}-on the user-facing field holding the URI for the item. The ContentResolver -will request the "{@code _data}" field for that record, and because -it has higher permissions than a client, it should be able to access -that file directly and return a read wrapper for the file to the client.
-
-
-
-
-For an example of a private content provider implementation, see the -NodePadProvider class in the Notepad sample application that ships with the SDK. -
- - -Declaring the content provider
- --To let the Android system know about the content provider you've developed, -declare it with a {@code <provider>} element in the application's -AndroidManifest.xml file. Content providers that are not declared in the -manifest are not visible to the Android system -
- --The {@code name} attribute is the fully qualified name of the ContentProvider -subclass. The {@code authorities} attribute is the authority part of the -{@code content:} URI that identifies the provider. -For example if the ContentProvider subclass is AutoInfoProvider, the -{@code <provider>} element might look like this: -
- --<provider android:name="com.example.autos.AutoInfoProvider" - android:authorities="com.example.autos.autoinfoprovider" - . . . /> -</provider> -- -
-Note that the {@code authorities} attribute omits the path part of a -{@code content:} URI. For example, if AutoInfoProvider controlled subtables -for different types of autos or different manufacturers, -
- -{@code content://com.example.autos.autoinfoprovider/honda}
-
{@code content://com.example.autos.autoinfoprovider/gm/compact}
-
{@code content://com.example.autos.autoinfoprovider/gm/suv}
-those paths would not be declared in the manifest. The authority is what -identifies the provider, not the path; your provider can interpret the path -part of the URI in any way you choose. -
- --Other {@code <provider>} attributes can set permissions to read and -write data, provide for an icon and text that can be displayed to users, -enable and disable the provider, and so on. Set the {@code multiprocess} -attribute to "{@code true}" if data does not need to be synchronized between -multiple running versions of the content provider. This permits an instance -of the provider to be created in each client process, eliminating the need -to perform IPC. -
- - -Content URI Summary
- --Here is a recap of the important parts of a content URI: -
- -
-
-
-
-
- Standard prefix indicating that the data is controlled by a -content provider. It's never modified. - -
The authority part of the URI; it identifies the content provider. -For third-party applications, this should be a fully-qualified class name -(reduced to lowercase) to ensure uniqueness. The authority is declared in -the {@code <provider>} element's {@code authorities} attribute:
- -<provider android:name=".TransportationProvider" - android:authorities="com.example.transportationprovider" - . . . >
-
-The path that the content provider uses to determine what kind of data is -being requested. This can be zero or more segments long. If the content provider -exposes only one type of data (only trains, for example), it can be absent. -If the provider exposes several types, including subtypes, it can be several -segments long — for example, "{@code land/bus}", "{@code land/train}", -"{@code sea/ship}", and "{@code sea/submarine}" to give four possibilities.
-
-The ID of the specific record being requested, if any. This is the -{@code _ID} value of the requested record. If the request is not limited to -a single record, this segment and the trailing slash are omitted:
- -{@code content://com.example.transportationprovider/trains}
-
-
-
+
- + + Content Provider Basics + +
- + How to access data in a content provider when the data is organized in tables. + +
- + + Creating a Content Provider + +
- + How to create your own content provider. + +
- + + Calendar Provider + +
- + How to access the Calendar Provider that is part of the Android platform. + +