+ Figure 1. The Choose Device window enables you to + select a physical Android device or a virtual device to debug your app.
+Android Studio enables you to debug apps running on the emulator or on an Android device. +With Android Studio, you can:
+ +To debug your app, Android Studio builds a debuggable version of your app, connects +to a device or to the emulator, installs the app and runs it. The IDE shows the system log +while your app is running and provides debugging tools to filter log messages, work with +breakpoints, and control the execution flow.
+ + +
+ Figure 1. The Choose Device window enables you to + select a physical Android device or a virtual device to debug your app.
+To run your app in debug mode, you build an APK signed with a debug key and install it on a +physical Android device or on the Android emulator. +To set up an Android device for development, see Using +Hardware Devices. For more information about the emulator provided by the Android SDK, see +Using the Emulator.
+ +To debug your app in Android Studio:
+ +
in the toolbar.Figure 1 shows the Choose Device window. The list shows all the Android devices
+connected to your computer. Select Launch Emulator to use an Android virtual device
+instead. Click the ellipsis 
to open the
+Android Virtual Device Manager.
Android Studio opens the Debug tool window when you debug your app. To open the
+Debug window manually, click Debug
+
.
+This window shows threads and variables in the Debugger tab, the device status in the
+Console tab, and the system log in the Logcat tab. The Debug tool
+window also provides other debugging tools covered in the following sections.
+Figure 2. The Debug tool window in Android Studio showing +the current thread and the object tree for a variable.
+ + +The system log shows system messages while you debug your app. These messages include +information from apps running on the device. If you want to use the +system log to debug your app, make sure your code writes log messages and prints the stack +trace for exceptions while your app is in the development phase.
+ +To write log messages in your code, use the {@link android.util.Log} class. Log messages +help you understand the execution flow by collecting the system debug output while you interact +with your app. Log messages can tell you what part of your application failed. For more +information about logging, see +Reading and Writing Logs.
+ +The following example shows how you might add log messages to determine if previous state +information is available when your activity starts:
+ +
+import android.util.Log;
+...
+public class MyActivity extends Activity {
+ private static final String TAG = MyActivity.class.getSimpleName();
+ ...
+ @Override
+ public void onCreate(Bundle savedInstanceState) {
+ if (savedInstanceState != null) {
+ Log.d(TAG, "onCreate() Restoring previous state");
+ /* restore state */
+ } else {
+ Log.d(TAG, "onCreate() No saved state available");
+ /* initialize app */
+ }
+ }
+}
+
+
+During development, your code can also catch exceptions and write the stack trace to the system +log:
+ +
+void someOtherMethod() {
+ try {
+ ...
+ } catch (SomeException e) {
+ Log.d(TAG, "someOtherMethod()", e);
+ }
+}
+
+
+Note: Remove debug log messages and stack trace print calls from
+your code when you are ready to publish your app. You could do this by setting a DEBUG
+flag and placing debug log messages inside conditional statements.
Both the Android DDMS (Dalvik Debug Monitor Server) and the Debug tool windows +show the system log; however, the Android DDMS tool window lets you view only log messages +for a particular process. To view the system log on the Android DDMS tool window:
+ +
to open the Android DDMS
+ tool window.
.
+Figure 4. The system log in the Android DDMS tool +window.
+ +The Android DDMS tool window gives you access to some DDMS features from Android Studio. +For more information about DDMS, see Using DDMS. +
+ +The system log shows messages from Android services and other Android apps. To filter the log +messages to view only the ones you are interested in, use the tools in the Android DDMS +window:
+ +
. If the Devices view
+ is not available, click Restore Devices View
+ 
on the right of the Android
+ DDMS tool window. This button is only visible when you hide the Devices
+ window.Breakpoints enable you to pause the execution of your app at a particular line of code, examine +variables, evaluate expressions, and continue the execution line by line. Use breakpoints to +determine the causes of run-time errors that you can't fix by looking at your code only. To debug +your app using breakpoints:
+ +Android Studio pauses the execution of your app when it reaches the breakpoint. You can then +use the tools in the Debug tool window to identify the cause of the error.
+ +
+Figure 5. A red dot appears next to the line when you set +a breakpoint.
+ +To view all the breakpoints and configure breakpoint settings, click View
+Breakpoints 
on the left side of the Debug tool
+window. The Breakpoints window appears, as shown in figure 6.
+Figure 6. The Breakpoints window lists all the current +breakpoints and includes behavior settings for each.
+ +The Breakpoints window lets you enable or disable each breakpoint from the +list on the left. If a breakpoint is disabled, Android Studio does not pause your app when +it hits that breakpoint. Select a breakpoint from the list to configure its settings. +You can configure a breakpoint to be disabled at first and have the system enable it after a +different breakpoint is hit. You can also configure whether a breakpoint should be disabled after +it is hit. To set a breakpoint for any exception, select Exception Breakpoints +in the list of breakpoints.
+ +After you set breakpoints in your code, click Rerun
+ to start the app again. When a breakpoint is
+hit, Android Studio pauses the app and highlights the breakpoint in the source code. The
+Debug tool window lets you examine variables and control the execution step by
+step:
To examine the object tree for a variable, expand it in the Variables view. If
+ the Variables view is not visible, click Restore Variables View
+ 
.
To evaluate an expression at the current execution point, click Evaluate
+ Expression 
.
To advance to the next line in the code (without entering a method), click Step
+ Over 
.
To advance to the first line inside a method call, click Step
+ Into 
.
To advance to the next line outside the current method, click Step
+ Out 
.
To continue running the app normally, click Resume Program
+ 
.
+Figure 7. The Variables view in the Debug tool window.
+ + +Even if your application does not generate runtime errors, this does not mean it is free of +problems. You should also consider the following issues:
+ +The Android Device Monitor is a stand-alone tool with a graphical user interface for serveral +Android application debugging and analysis tools, including the Dalvik Debug Monitor Server (DDMS). +You can use the Android Device Monitor to analyze memory usage, profile methods, +monitor network traffic and simulate incoming calls and messages.
+ +To open the Android Device Monitor from Android Studio, click
+Monitor 
on the toolbar. The Android Device Monitor
+opens in a new window.
For more information about the Android Device Monitor and DDMS, see +Device Monitor and +Using DDMS.
+ + +Android Studio enables you to capture a screenshot or a short video of the device screen +while your app is running. Screenshots and videos are useful as promotional materials for your +app, and you can also attach them to bug reports that you send to your development team.
+ +To take a screenshot of your app:
+ + to open the Android DDMS
+ tool window.
on the left side of the
+ Android DDMS tool window.To take a video recording of your app:
+ + to open the Android DDMS
+ tool window.
on the left side of the
+ Android DDMS tool window.