Android中CheckBox与CompoundButton源码解析[通俗易懂]

大家好，又见面了，我是你们的朋友全栈君。

经历过了前面一系列的讲解，下面我们直接来看看系统里面的CheckBox与CompoundButton类的源码文件。你肯定会发现很多熟悉的地方。
结合下面源码，我们对它们进行解析解析，它里面使用的就是自定义drawable state。

我们首先直接看CheckBox的源码

public class CheckBox extends CompoundButton { 
   
    public CheckBox(Context context) {
        this(context, null);
    }

    public CheckBox(Context context, AttributeSet attrs) {
        this(context, attrs, com.android.internal.R.attr.checkboxStyle);
    }

    public CheckBox(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
        super.onInitializeAccessibilityEvent(event);
        event.setClassName(CheckBox.class.getName());
    }

    @Override
    public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
        super.onInitializeAccessibilityNodeInfo(info);
        info.setClassName(CheckBox.class.getName());
    }
}

我们可以看到，它里面并没有做什么，因为它的操作都是继承自CompoundButton.

我们先来看看下面一个普通的布局文件：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">

    <CheckBox
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="CheckBox"/>

</RelativeLayout>

在上面的这个相对布局中，就写了一个CheckBox，我们什么都不做，直接运行代码，就会看到下面的运行界面：

当我们单击这个CheckBox,我们发现他会被选中，那么它内部到底是怎么实现的呢？
其实使用过drawable state的人应该对这个并不陌生，我们经常这样做：

1、在res/drawable文件下创建selector.xml，示例代码如下：

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item  android:state_pressed="false" android:drawable="@drawable/title_button_back">
    </item>
    <item  android:state_pressed="true" android:drawable="@drawable/title_button_back_h">
    </item>
    <item  android:state_window_focused="false" android:drawable="@drawable/title_button_back">
    </item>
</selector>

2、编写布局文件，为布局文件中的ImageButton设置selector，示例代码如下：

<?xml version="1.0" encoding="utf-8"?>  
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_height="wrap_content" android:layout_width="fill_parent">  
    <ImageButton android:id="@+id/title_IB" android:layout_height="wrap_content" android:layout_width="wrap_content" android:background="#00000000" android:layout_marginRight="4dp" android:layout_centerVertical="true" android:src="@drawable/selector">
    </ImageButton>  
</RelativeLayout>

当我们单击这个图片按钮的时候，图片按钮的图片就会发生变化，其实CheckBox也是这样做的，只是这些系统为我们做了。

下面我们来看看系统实现源码：
上面在布局文件中直接写了一个CheckBox,布局文件被解析后就会实例化这个CheckBox对象，就会执行CheckBox的构造函数：

public CheckBox(Context context, AttributeSet attrs) {
    this(context, attrs, com.android.internal.R.attr.checkboxStyle);
}

public CheckBox(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
}

从上面我们可以知道两点：
1、CheckBox的默认样式是com.android.internal.R.attr.checkboxStyle
2、最终执行的时候CompoundButton的构造函数

在frameworks/base/core/res/res/values/themes.xml文件中，已经初始化了checkBoxStyle样式：

<item name="checkboxStyle">@android:style/Widget.CompoundButton.CheckBox</item>

在frameworks/base/core/res/res/values/styles.xml文件，我们来看看它的样式是什么：

<style name="Widget.CompoundButton.CheckBox"> <item name="android:button">?android:attr/listChoiceIndicatorMultiple</item> </style>

在frameworks/base/core/res/res/values/themes.xml文件：

<item name="listChoiceIndicatorMultiple">@android:drawable/btn_check</item>

可以看到，CheckBox的默认样式就是给它的button属性赋值了一个btn_check,我们来看看btn_check文件里面的具体内容。

在frameworks/base/core/res/res/drawable/btn_check.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <!-- Enabled states -->

    <item android:state_checked="true" android:state_window_focused="false" android:state_enabled="true" android:drawable="@drawable/btn_check_on" />
    <item android:state_checked="false" android:state_window_focused="false" android:state_enabled="true" android:drawable="@drawable/btn_check_off" />

    <item android:state_checked="true" android:state_pressed="true" android:state_enabled="true" android:drawable="@drawable/btn_check_on_pressed" />
    <item android:state_checked="false" android:state_pressed="true" android:state_enabled="true" android:drawable="@drawable/btn_check_off_pressed" />

    <item android:state_checked="true" android:state_focused="true" android:state_enabled="true" android:drawable="@drawable/btn_check_on_selected" />
    <item android:state_checked="false" android:state_focused="true" android:state_enabled="true" android:drawable="@drawable/btn_check_off_selected" />

    <item android:state_checked="false" android:state_enabled="true" android:drawable="@drawable/btn_check_off" />
    <item android:state_checked="true" android:state_enabled="true" android:drawable="@drawable/btn_check_on" />


    <!-- Disabled states -->

    <item android:state_checked="true" android:state_window_focused="false" android:drawable="@drawable/btn_check_on_disable" />
    <item android:state_checked="false" android:state_window_focused="false" android:drawable="@drawable/btn_check_off_disable" />

    <item android:state_checked="true" android:state_focused="true" android:drawable="@drawable/btn_check_on_disable_focused" />
    <item android:state_checked="false" android:state_focused="true" android:drawable="@drawable/btn_check_off_disable_focused" />

    <item android:state_checked="false" android:drawable="@drawable/btn_check_off_disable" />
    <item android:state_checked="true" android:drawable="@drawable/btn_check_on_disable" />

</selector>

我们看到，state_checked为true的时候，drawable=”@drawable/btn_check_on”，state_checked为false的时候,drawable=”@drawable/btn_check_off”.
@drawable/btn_check_on图片和@drawable/btn_check_off图片，在frameworks/base/core/res/res/drawable我们可以找到：

我们可以看到，其实就是根据不同的状态，为button属性赋值了不同的图片资源，这就是我们看到的效果。

state_checked这个状态的定义，在下面进行了定义：

<declare-styleable name="DrawableStates">
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}, set when a view has input focus. -->
    <attr name="state_focused" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}, set when a view's window has input focus. -->
    <attr name="state_window_focused" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}, set when a view is enabled. -->
    <attr name="state_enabled" format="boolean" />
    <!-- State identifier indicating that the object <var>may</var> display a check mark. See {@link R.attr#state_checked} for the identifier that indicates whether it is actually checked. -->
    <attr name="state_checkable" format="boolean"/>
    <!-- State identifier indicating that the object is currently checked. See {@link R.attr#state_checkable} for an additional identifier that can indicate if any object may ever display a check, regardless of whether state_checked is currently set. -->
    <attr name="state_checked" format="boolean"/>
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}, set when a view (or one of its parents) is currently selected. -->
    <attr name="state_selected" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}, set when the user is pressing down in a view. -->
    <attr name="state_pressed" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}, set when a view or its parent has been "activated" meaning the user has currently marked it as being of interest. This is an alternative representation of state_checked for when the state should be propagated down the view hierarchy. -->
    <attr name="state_activated" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}.-->
    <attr name="state_active" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}.-->
    <attr name="state_single" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}.-->
    <attr name="state_first" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}.-->
    <attr name="state_middle" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}.-->
    <attr name="state_last" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}, indicating that the Drawable is in a view that is hardware accelerated. This means that the device can at least render a full-screen scaled bitmap with one layer of text and bitmaps composited on top of it at 60fps. When this is set, the colorBackgroundCacheHint will be ignored even if it specifies a solid color, since that optimization is not needed. -->
    <attr name="state_accelerated" format="boolean" />
    <!-- State value for {@link android.graphics.drawable.StateListDrawable StateListDrawable}, set when a pointer is hovering over the view. -->
    <attr name="state_hovered" format="boolean" />
    <!-- State for {@link android.graphics.drawable.StateListDrawable StateListDrawable} indicating that the Drawable is in a view that is capable of accepting a drop of the content currently being manipulated in a drag-and-drop operation. -->
    <attr name="state_drag_can_accept" format="boolean" />
    <!-- State for {@link android.graphics.drawable.StateListDrawable StateListDrawable} indicating that a drag operation (for which the Drawable's view is a valid recipient) is currently positioned over the Drawable. -->
    <attr name="state_drag_hovered" format="boolean" />
    <!-- State for {@link android.graphics.drawable.StateListDrawable StateListDrawable} indicating that a View has accessibility focus. -->
    <attr name="state_accessibility_focused" format="boolean" />
</declare-styleable>

我们可以看到<attr name="state_checked" format="boolean"/>

下面我们看看CompoundButton的构造函数，因为CheckBox最终执行的是它的构造函数。

public CompoundButton(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);

    TypedArray a =
            context.obtainStyledAttributes(
                    attrs, com.android.internal.R.styleable.CompoundButton, defStyle, 0);

    Drawable d = a.getDrawable(com.android.internal.R.styleable.CompoundButton_button);
    if (d != null) {
        setButtonDrawable(d);
    }

    boolean checked = a
            .getBoolean(com.android.internal.R.styleable.CompoundButton_checked, false);
    setChecked(checked);

    a.recycle();
}

我们可以知道CompoundButton自定义了两个属性，进入frameworks/base/core/res/res/values/attrs.xml文件：

<declare-styleable name="CompoundButton">
    <!-- Indicates the initial checked state of this button. -->
    <attr name="checked" format="boolean" />
    <!-- Drawable used for the button graphic (e.g. checkbox, radio button, etc). -->
    <attr name="button" format="reference"/>
</declare-styleable>

我们可以看到它定义了两个属性：checked，button，一个存放的是一个boolean类型的值，表示是否被选中，一个存放的是引用类型，对应的是一个图片。
在构造函数中，我们获取到了这两个属性值。上面就是对button这个属性进行了默认赋值，然后我们这里就可以获取到上面的btn_check这个xml文件的drawable。
也就是说Drawable d = a.getDrawable(com.android.internal.R.styleable.CompoundButton_button)中的d的到的就是btn_check这个xml文件的drawable。

然后分别调用了setButtonDrawable(d)和setChecked(checked)来对我们自定义的控件进行了设置。

我们来看看setButtonDrawable(d)函数：

public void setButtonDrawable(Drawable d) {
    if (d != null) {
        if (mButtonDrawable != null) {
            mButtonDrawable.setCallback(null);
            unscheduleDrawable(mButtonDrawable);
        }
        //这里设置Callback的原因就是refreshDrawableState刷新的时候可以回调到invalidateDrawable
        //这样就可以重绘，这个我们在#详解refreshDrawableList()的执行流程#这篇文件讲过
        d.setCallback(this);
        d.setVisible(getVisibility() == VISIBLE, false);
        mButtonDrawable = d;
        setMinHeight(mButtonDrawable.getIntrinsicHeight());
    }

    refreshDrawableState();
}

最后调用了refreshDrawableState这个方法，这个执行过程我们也分析过，整个执行思路都是一样，不过不同的是，里面的很多方法都被覆盖了。

这里我们再来把整个思路走一走。

refreshDrawableState执行的还是View里面的这个方法，直接看源码。

public void refreshDrawableState() {
    //首先把标志设置为PFLAG_DRAWABLE_STATE_DIRTY
    mPrivateFlags |= PFLAG_DRAWABLE_STATE_DIRTY;
    drawableStateChanged();

    ViewParent parent = mParent;
    if (parent != null) {
        parent.childDrawableStateChanged(this);
    }
}

drawableStateChanged这个方法不在执行View里面的这个方法，因为CompoundButton里面有这个方法，我们看看CompoundButton的这个方法。

@Override
protected void drawableStateChanged() {
    super.drawableStateChanged();

    if (mButtonDrawable != null) {
        int[] myDrawableState = getDrawableState();

        // Set the state of the Drawable
        mButtonDrawable.setState(myDrawableState);

        invalidate();
    }
}

getDrawableState这个函数还是调用的View的这个函数。

public final int[] getDrawableState() {
    //PFLAG_DRAWABLE_STATE_DIRTY是前面refreshDrawableState设置的
    //如果mDrawableState不为空，并且不需要刷新状态，则直接返回，否则重新进行获取
    if ((mDrawableState != null) && ((mPrivateFlags & PFLAG_DRAWABLE_STATE_DIRTY) == 0)) {
        return mDrawableState;
    } else {
        //这里就是重新得到视图状态，并将其返回
        mDrawableState = onCreateDrawableState(0);
        //清除前面refreshDrawableState设置的标识
        mPrivateFlags &= ~PFLAG_DRAWABLE_STATE_DIRTY;
        return mDrawableState;
    }
}

下面调用到了onCreateDrawableState这个方法，这个方法也不在是执行View里面的这个方法，因为CompoundButton里面也有这个方法。

@Override
protected int[] onCreateDrawableState(int extraSpace) {
    final int[] drawableState = super.onCreateDrawableState(extraSpace + 1);
    if (isChecked()) {
        mergeDrawableStates(drawableState, CHECKED_STATE_SET);
    }
    return drawableState;
}

结合之前我们详解refreshDrawableList()的执行流程的分析。这个方法就是在之前的基础上加入了一个判断，如果isChekced为真，就把我们自定义的这个状态加进去，这样当前状态里面就有我们的自定义的状态，后面在状态二维数组中查询的时候，就可以找到对应的drawable图片进行设置了。

这个函数执行完了就会回到上面的getDrawableState函数，然后把当前的状态返回到drawableStateChanged函数中，接着看里面的代码。

接着执行mButtonDrawable.setState(myDrawableState)，把得到的当前状态数组设置进去。里面的执行过去前面详解refreshDrawableList()的执行流程的分析也说过，是完全一样的，我们就省略,不明白就再看看，最后会执行invalidateSelf函数。

这个函数就会得到前面我们设置的Callback回调，调用它的invalidateDrawable方法。

public void invalidateSelf() {
    final Callback callback = getCallback();
    if (callback != null) {
        callback.invalidateDrawable(this);
    }
}

跟前面一样，因为View实现了这个回调，所以它执行的是View里面的实现方法。在这个方法里面执行了invalidate函数，所以会执行onDraw方法.
在CompoundButton里面实现了这个方法，它不再直接执行View里面的这个方法了。

protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    final Drawable buttonDrawable = mButtonDrawable;
    if (buttonDrawable != null) {
        final int verticalGravity = getGravity() & Gravity.VERTICAL_GRAVITY_MASK;
        final int drawableHeight = buttonDrawable.getIntrinsicHeight();
        final int drawableWidth = buttonDrawable.getIntrinsicWidth();

        int top = 0;
        switch (verticalGravity) {
            case Gravity.BOTTOM:
                top = getHeight() - drawableHeight;
                break;
            case Gravity.CENTER_VERTICAL:
                top = (getHeight() - drawableHeight) / 2;
                break;
        }
        int bottom = top + drawableHeight;
        int left = isLayoutRtl() ? getWidth() - drawableWidth : 0;
        int right = isLayoutRtl() ? getWidth() : drawableWidth;

        buttonDrawable.setBounds(left, top, right, bottom);
        buttonDrawable.draw(canvas);
    }
}

这样这个图片就绘制出来了，从btn_check里面我们可以看到最开始显示的图片是btn_check_off，当我们单击这个CheckBox的时候，会执行performClick函数。

@Override
public boolean performClick() {
    /* * XXX: These are tiny, need some surrounding 'expanded touch area', * which will need to be implemented in Button if we only override * performClick() */

    /* When clicked, toggle the state */
    toggle();
    return super.performClick();
}

接着执行toggle函数。

public void toggle() {
    setChecked(!mChecked);
}

这里面就把当前的状态设置为与之前相反的状态，刚开始为false,这个时候就为true.

接着我们看看setChecked函数。

public void setChecked(boolean checked) {
    if (mChecked != checked) {
        mChecked = checked;
        refreshDrawableState();
        notifyViewAccessibilityStateChangedIfNeeded(
                AccessibilityEvent.CONTENT_CHANGE_TYPE_UNDEFINED);

        // Avoid infinite recursions if setChecked() is called from a listener
        if (mBroadcasting) {
            return;
        }

        mBroadcasting = true;
        if (mOnCheckedChangeListener != null) {
            mOnCheckedChangeListener.onCheckedChanged(this, mChecked);
        }
        if (mOnCheckedChangeWidgetListener != null) {
            mOnCheckedChangeWidgetListener.onCheckedChanged(this, mChecked);
        }

        mBroadcasting = false;            
    }
}

在这个里面又执行了refreshDrawableState函数，同样把上面的refreshDrawableState过程又执行了一遍，执行在到onCreateDrawableState就不一样了。
我们在来看看这个函数：

protected int[] onCreateDrawableState(int extraSpace) {
    final int[] drawableState = super.onCreateDrawableState(extraSpace + 1);
    if (isChecked()) {
        mergeDrawableStates(drawableState, CHECKED_STATE_SET);
    }
    return drawableState;
}

第一次执行的时候isChecked为false,自定义的这个状态没有合进去，这次就把自定义的这个状态合进去，这样就可以查询到我们的状态，所以就可以找到定义的drawable,所以图片发生改变为btn_check_on。

最后把完整的CompoundButton源码贴出来，可以对照上面将的，然后再根据前面讲的详解refreshDrawableList()的执行流程这个过程理解理解。

/* * Copyright (C) 2007 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 com.android.internal.R;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.os.Parcel;
import android.os.Parcelable;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.ViewDebug;
import android.view.accessibility.AccessibilityEvent;
import android.view.accessibility.AccessibilityNodeInfo;

/** * <p> * A button with two states, checked and unchecked. When the button is pressed * or clicked, the state changes automatically. * </p> * * <p><strong>XML attributes</strong></p> * <p> * See {@link android.R.styleable#CompoundButton * CompoundButton Attributes}, {@link android.R.styleable#Button Button * Attributes}, {@link android.R.styleable#TextView TextView Attributes}, {@link * android.R.styleable#View View Attributes} * </p> */
public abstract class CompoundButton extends Button implements Checkable { 
   
    private boolean mChecked;
    private int mButtonResource;
    private boolean mBroadcasting;
    private Drawable mButtonDrawable;
    private OnCheckedChangeListener mOnCheckedChangeListener;
    private OnCheckedChangeListener mOnCheckedChangeWidgetListener;

    private static final int[] CHECKED_STATE_SET = {
        R.attr.state_checked
    };

    public CompoundButton(Context context) {
        this(context, null);
    }

    public CompoundButton(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public CompoundButton(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        TypedArray a =
                context.obtainStyledAttributes(
                        attrs, com.android.internal.R.styleable.CompoundButton, defStyle, 0);

        Drawable d = a.getDrawable(com.android.internal.R.styleable.CompoundButton_button);
        if (d != null) {
            setButtonDrawable(d);
        }

        boolean checked = a
                .getBoolean(com.android.internal.R.styleable.CompoundButton_checked, false);
        setChecked(checked);

        a.recycle();
    }

    public void toggle() {
        setChecked(!mChecked);
    }

    @Override
    public boolean performClick() {
        /* * XXX: These are tiny, need some surrounding 'expanded touch area', * which will need to be implemented in Button if we only override * performClick() */

        /* When clicked, toggle the state */
        toggle();
        return super.performClick();
    }

    @ViewDebug.ExportedProperty
    public boolean isChecked() {
        return mChecked;
    }

    /** * <p>Changes the checked state of this button.</p> * * @param checked true to check the button, false to uncheck it */
    public void setChecked(boolean checked) {
        if (mChecked != checked) {
            mChecked = checked;
            refreshDrawableState();
            notifyViewAccessibilityStateChangedIfNeeded(
                    AccessibilityEvent.CONTENT_CHANGE_TYPE_UNDEFINED);

            // Avoid infinite recursions if setChecked() is called from a listener
            if (mBroadcasting) {
                return;
            }

            mBroadcasting = true;
            if (mOnCheckedChangeListener != null) {
                mOnCheckedChangeListener.onCheckedChanged(this, mChecked);
            }
            if (mOnCheckedChangeWidgetListener != null) {
                mOnCheckedChangeWidgetListener.onCheckedChanged(this, mChecked);
            }

            mBroadcasting = false;            
        }
    }

    /** * Register a callback to be invoked when the checked state of this button * changes. * * @param listener the callback to call on checked state change */
    public void setOnCheckedChangeListener(OnCheckedChangeListener listener) {
        mOnCheckedChangeListener = listener;
    }

    /** * Register a callback to be invoked when the checked state of this button * changes. This callback is used for internal purpose only. * * @param listener the callback to call on checked state change * @hide */
    void setOnCheckedChangeWidgetListener(OnCheckedChangeListener listener) {
        mOnCheckedChangeWidgetListener = listener;
    }

    /** * Interface definition for a callback to be invoked when the checked state * of a compound button changed. */
    public static interface OnCheckedChangeListener { 
   
        /** * Called when the checked state of a compound button has changed. * * @param buttonView The compound button view whose state has changed. * @param isChecked The new checked state of buttonView. */
        void onCheckedChanged(CompoundButton buttonView, boolean isChecked);
    }

    /** * Set the background to a given Drawable, identified by its resource id. * * @param resid the resource id of the drawable to use as the background */
    public void setButtonDrawable(int resid) {
        if (resid != 0 && resid == mButtonResource) {
            return;
        }

        mButtonResource = resid;

        Drawable d = null;
        if (mButtonResource != 0) {
            d = getResources().getDrawable(mButtonResource);
        }
        setButtonDrawable(d);
    }

    /** * Set the background to a given Drawable * * @param d The Drawable to use as the background */
    public void setButtonDrawable(Drawable d) {
        if (d != null) {
            if (mButtonDrawable != null) {
                mButtonDrawable.setCallback(null);
                unscheduleDrawable(mButtonDrawable);
            }
            d.setCallback(this);
            d.setVisible(getVisibility() == VISIBLE, false);
            mButtonDrawable = d;
            setMinHeight(mButtonDrawable.getIntrinsicHeight());
        }

        refreshDrawableState();
    }

    @Override
    public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
        super.onInitializeAccessibilityEvent(event);
        event.setClassName(CompoundButton.class.getName());
        event.setChecked(mChecked);
    }

    @Override
    public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
        super.onInitializeAccessibilityNodeInfo(info);
        info.setClassName(CompoundButton.class.getName());
        info.setCheckable(true);
        info.setChecked(mChecked);
    }

    @Override
    public int getCompoundPaddingLeft() {
        int padding = super.getCompoundPaddingLeft();
        if (!isLayoutRtl()) {
            final Drawable buttonDrawable = mButtonDrawable;
            if (buttonDrawable != null) {
                padding += buttonDrawable.getIntrinsicWidth();
            }
        }
        return padding;
    }

    @Override
    public int getCompoundPaddingRight() {
        int padding = super.getCompoundPaddingRight();
        if (isLayoutRtl()) {
            final Drawable buttonDrawable = mButtonDrawable;
            if (buttonDrawable != null) {
                padding += buttonDrawable.getIntrinsicWidth();
            }
        }
        return padding;
    }

    /** * @hide */
    @Override
    public int getHorizontalOffsetForDrawables() {
        final Drawable buttonDrawable = mButtonDrawable;
        return (buttonDrawable != null) ? buttonDrawable.getIntrinsicWidth() : 0;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        final Drawable buttonDrawable = mButtonDrawable;
        if (buttonDrawable != null) {
            final int verticalGravity = getGravity() & Gravity.VERTICAL_GRAVITY_MASK;
            final int drawableHeight = buttonDrawable.getIntrinsicHeight();
            final int drawableWidth = buttonDrawable.getIntrinsicWidth();

            int top = 0;
            switch (verticalGravity) {
                case Gravity.BOTTOM:
                    top = getHeight() - drawableHeight;
                    break;
                case Gravity.CENTER_VERTICAL:
                    top = (getHeight() - drawableHeight) / 2;
                    break;
            }
            int bottom = top + drawableHeight;
            int left = isLayoutRtl() ? getWidth() - drawableWidth : 0;
            int right = isLayoutRtl() ? getWidth() : drawableWidth;

            buttonDrawable.setBounds(left, top, right, bottom);
            buttonDrawable.draw(canvas);
        }
    }

    @Override
    protected int[] onCreateDrawableState(int extraSpace) {
        final int[] drawableState = super.onCreateDrawableState(extraSpace + 1);
        if (isChecked()) {
            mergeDrawableStates(drawableState, CHECKED_STATE_SET);
        }
        return drawableState;
    }

    @Override
    protected void drawableStateChanged() {
        super.drawableStateChanged();

        if (mButtonDrawable != null) {
            int[] myDrawableState = getDrawableState();

            // Set the state of the Drawable
            mButtonDrawable.setState(myDrawableState);

            invalidate();
        }
    }

    @Override
    protected boolean verifyDrawable(Drawable who) {
        return super.verifyDrawable(who) || who == mButtonDrawable;
    }

    @Override
    public void jumpDrawablesToCurrentState() {
        super.jumpDrawablesToCurrentState();
        if (mButtonDrawable != null) mButtonDrawable.jumpToCurrentState();
    }

    static class SavedState extends BaseSavedState {
        boolean checked;

        /** * Constructor called from {@link CompoundButton#onSaveInstanceState()} */
        SavedState(Parcelable superState) {
            super(superState);
        }

        /** * Constructor called from {@link #CREATOR} */
        private SavedState(Parcel in) {
            super(in);
            checked = (Boolean)in.readValue(null);
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeValue(checked);
        }

        @Override
        public String toString() {
            return "CompoundButton.SavedState{"
                    + Integer.toHexString(System.identityHashCode(this))
                    + " checked=" + checked + "}";
        }

        public static final Parcelable.Creator<SavedState> CREATOR
                = new Parcelable.Creator<SavedState>() {
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }

    @Override
    public Parcelable onSaveInstanceState() {
        // Force our ancestor class to save its state
        setFreezesText(true);
        Parcelable superState = super.onSaveInstanceState();

        SavedState ss = new SavedState(superState);

        ss.checked = isChecked();
        return ss;
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        SavedState ss = (SavedState) state;

        super.onRestoreInstanceState(ss.getSuperState());
        setChecked(ss.checked);
        requestLayout();
    }
}