https://source.android.com/ 
/*
 * 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.

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 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
            }
        });
    }
}


The above snippet creates an instance of OnClickListener and wires the listener to the button using setOnClickListener(View.OnClickListener). As a result, the system executes the code you write in onClick(View) after the user presses the button.


The system executes the code in 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.


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.


For all XML style attributes available on Button see Button Attributes, TextView Attributes, View Attributes. See the Styles and Themes
guide to learn how to implement and organize overrides to style-related attributes.


/**
 * 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>
 * &lt;Button
 *     android:id="@+id/button_id"
 *     android:layout_height="wrap_content"
 *     android:layout_width="wrap_content"
 *     android:text="@string/self_destruct" /&gt;</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.

Params:
  • context – The Context the Button is running in, through which it can
       access the current theme, resources, etc.
See Also:
/**
     * 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);
    }

    
LayoutInflater calls this constructor when inflating a Button from XML. The attributes defined by the current theme's 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.

Params:
  • context – The Context the view is running in, through which it can
       access the current theme, resources, etc.
  • attrs – The attributes of the XML Button tag being used to inflate the view.
See Also:
/**
     * {@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 defStyleAttr override base view attributes. 
For Button's base view attributes see Button Attributes, TextView Attributes, View Attributes. 
Params:
  • context – The Context the Button is running in, through which it can
       access the current theme, resources, etc.
  • attrs – The attributes of the XML Button tag that is inflating the view.
  • 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 Also:
/**
     * 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 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 View(Context, AttributeSet, int, int). 
Params:
  • context – The Context the Button is running in, through which it can
       access the current theme, resources, etc.
  • attrs – The attributes of the XML Button tag that is inflating the view.
  • 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.
  • 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 Also:
/**
     * 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);
    }

    @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);
    }
}