A typical use of a push-button in an activity would be the following: - *
+ * A user interface element the user can tap or click to perform an action. + * + *To display a button in an activity, add a button to the activity's layout XML file:
+ * + *+ * <Button + * android:id="@+id/button_id" + * android:layout_height="wrap_content" + * android:layout_width="wrap_content" + * android:text="@string/self_destruct" />+ * + *
To specify an action when the button is pressed, set a click + * listener on the button object in the corresponding activity code:
* *
* public class MyActivity extends Activity {
- * protected void onCreate(Bundle icicle) {
- * super.onCreate(icicle);
+ * protected void onCreate(Bundle savedInstanceState) {
+ * super.onCreate(savedInstanceState);
*
* setContentView(R.layout.content_layout_id);
*
* final Button button = findViewById(R.id.button_id);
* button.setOnClickListener(new View.OnClickListener() {
* public void onClick(View v) {
- * // Perform action on click
+ * // Code here executes on main thread after user presses button
* }
* });
* }
* }
*
- * However, instead of applying an {@link android.view.View.OnClickListener OnClickListener} to - * the button in your activity, you can assign a method to your button in the XML layout, - * using the {@link android.R.attr#onClick android:onClick} attribute. For example:
+ *The above snippet creates an instance of {@link View.OnClickListener} and wires + * the listener to the button using + * {@link #setOnClickListener setOnClickListener(View.OnClickListener)}. + * As a result, the system executes the code you write in {@code onClick(View)} after the + * user presses the button.
* - *- * <Button - * android:layout_height="wrap_content" - * android:layout_width="wrap_content" - * android:text="@string/self_destruct" - * android:onClick="selfDestruct" />+ *
The system executes the code in {@code onClick} on the + * main thread. + * This means your onClick code must execute quickly to avoid delaying your app's response + * to further user actions. See + * Keeping Your App Responsive + * for more details.
* - *Now, when a user clicks the button, the Android system calls the activity's {@code - * selfDestruct(View)} method. In order for this to work, the method must be public and accept - * a {@link android.view.View} as its only parameter. For example:
- * - *
- * public void selfDestruct(View view) {
- * // Kabloey
- * }
- *
- * The {@link android.view.View} passed into the method is a reference to the widget - * that was clicked.
- * - *Every Button is styled using the system's default button background, which is often different - * from one device to another and from one version of the platform to another. If you're not - * satisfied with the default button style and want to customize it to match the design of your - * application, then you can replace the button's background image with a state list drawable. - * A state list drawable is a drawable resource defined in XML that changes its image based on - * the current state of the button. Once you've defined a state list drawable in XML, you can apply - * it to your Button with the {@link android.R.attr#background android:background} - * attribute. For more information and an example, see State List - * Drawable.
- * - *See the Buttons + *
Every button is styled using the system's default button background, which is often + * different from one version of the platform to another. If you are not satisfied with the + * default button style, you can customize it. For more details and code samples, see the + * Styling Your Button * guide.
* - *XML attributes
- *- * See {@link android.R.styleable#Button Button Attributes}, + *
For all XML style attributes available on Button see + * {@link android.R.styleable#Button Button Attributes}, * {@link android.R.styleable#TextView TextView Attributes}, - * {@link android.R.styleable#View View Attributes} - *
+ * {@link android.R.styleable#View View Attributes}. See the + * {@link Styles and Themes + * guide to learn how to implement and organize overrides to style-related attributes. + * + * @see + * Buttons Guide + * {@link android.R.styleable#Button Styleable Button Attributes}, + * {@link android.R.styleable#TextView Styleable TextView Attributes}, + * {@link android.R.styleable#View Styleable View Attributes}, + * */ @RemoteView public class Button extends TextView { + + /** + * Simple constructor to use when creating a button from code. + * + * @param context The Context the Button is running in, through which it can + * access the current theme, resources, etc. + * + * @see #Button(Context, AttributeSet) + */ public Button(Context context) { this(context, null); } + /** + * {@link LayoutInflater} calls this constructor when inflating a Button from XML. + * The attributes defined by the current theme's + * {@link android.R.attr#buttonStyle android:buttonStyle} + * override base view attributes. + * + * You typically do not call this constructor to create your own button instance in code. + * However, you must override this constructor when + * creating custom views. + * + * @param context The Context the view is running in, through which it can + * access the current theme, resources, etc. + * @param attrs The attributes of the XML Button tag being used to inflate the view. + * + * @see #Button(Context, AttributeSet, int) + * @see android.view.View#View(Context, AttributeSet) + */ public Button(Context context, AttributeSet attrs) { this(context, attrs, com.android.internal.R.attr.buttonStyle); } + /** + * This constructor allows a Button subclass to use its own class-specific base style from a + * theme attribute when inflating. The attributes defined by the current theme's + * {@code defStyleAttr} override base view attributes. + * + *For Button's base view attributes see + * {@link android.R.styleable#Button Button Attributes}, + * {@link android.R.styleable#TextView TextView Attributes}, + * {@link android.R.styleable#View View Attributes}. + * + * @param context The Context the Button is running in, through which it can + * access the current theme, resources, etc. + * @param attrs The attributes of the XML Button tag that is inflating the view. + * @param defStyleAttr The resource identifier of an attribute in the current theme + * whose value is the the resource id of a style. The specified style’s + * attribute values serve as default values for the button. Set this parameter + * to 0 to avoid use of default values. + * @see #Button(Context, AttributeSet, int, int) + * @see android.view.View#View(Context, AttributeSet, int) + */ public Button(Context context, AttributeSet attrs, int defStyleAttr) { this(context, attrs, defStyleAttr, 0); } + /** + * This constructor allows a Button subclass to use its own class-specific base style from + * either a theme attribute or style resource when inflating. To see how the final value of a + * particular attribute is resolved based on your inputs to this constructor, see + * {@link android.view.View#View(Context, AttributeSet, int, int)}. + * + * @param context The Context the Button is running in, through which it can + * access the current theme, resources, etc. + * @param attrs The attributes of the XML Button tag that is inflating the view. + * @param defStyleAttr The resource identifier of an attribute in the current theme + * whose value is the the resource id of a style. The specified style’s + * attribute values serve as default values for the button. Set this parameter + * to 0 to avoid use of default values. + * @param defStyleRes The identifier of a style resource that + * supplies default values for the button, used only if + * defStyleAttr is 0 or cannot be found in the theme. + * Set this parameter to 0 to avoid use of default values. + * + * @see #Button(Context, AttributeSet, int) + * @see android.view.View#View(Context, AttributeSet, int, int) + */ public Button(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) { super(context, attrs, defStyleAttr, defStyleRes); }