Java tutorial
/* * Copyright (C) 2006 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.widget; import android.content.Context; import android.util.AttributeSet; import android.view.LayoutInflater; import android.view.MotionEvent; import android.view.PointerIcon; import android.widget.RemoteViews.RemoteView; /** * A user interface element the user can tap or click to perform an action. * * <p>To display a button in an activity, add a button to the activity's layout XML file:</p> * * <pre> * <Button * android:id="@+id/button_id" * android:layout_height="wrap_content" * android:layout_width="wrap_content" * android:text="@string/self_destruct" /></pre> * * <p>To specify an action when the button is pressed, set a click * listener on the button object in the corresponding activity code:</p> * * <pre> * public class MyActivity extends Activity { * 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) { * // Code here executes on main thread after user presses button * } * }); * } * }</pre> * * <p>The above snippet creates an instance of {@link android.view.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.</p> * * <p class="note">The system executes the code in {@code onClick} on the * <a href="{@docRoot}guide/components/processes-and-threads.html#Threads">main thread</a>. * This means your onClick code must execute quickly to avoid delaying your app's response * to further user actions. See * <a href="{@docRoot}training/articles/perf-anr.html">Keeping Your App Responsive</a> * for more details.</p> * * <p>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 * <a href="{@docRoot}guide/topics/ui/controls/button.html#Style">Styling Your Button</a> * guide.</p> * * <p>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}. See the * <a href="{@docRoot}guide/topics/ui/themes.html#ApplyingStyles">Styles and Themes</a> * guide to learn how to implement and organize overrides to style-related attributes.</p> */ @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 * <a href="{@docRoot}training/custom-views/index.html">creating custom views</a>. * * @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. * * <p>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 styles * 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 styles * 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); } @Override public CharSequence getAccessibilityClassName() { return Button.class.getName(); } @Override public PointerIcon onResolvePointerIcon(MotionEvent event, int pointerIndex) { if (getPointerIcon() == null && isClickable() && isEnabled()) { return PointerIcon.getSystemIcon(getContext(), PointerIcon.TYPE_HAND); } return super.onResolvePointerIcon(event, pointerIndex); } }