滑动的Button

2022-10-20 10:59:28

在介绍SwitchButton之前，先来看一下系统Button是如何实现的。源码如下：

@RemoteView
public class Button extends TextView {
public Button(Context context) {
this(context, null);
}
public Button(Context context, AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.buttonStyle);
}
public Button(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
@Override
public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(event);
event.setClassName(Button. class.getName());
}
@Override
public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
super.onInitializeAccessibilityNodeInfo(info);
info.setClassName(Button. class.getName());
}
}

@RemoteView

public class Button extends TextView {

    public Button(Context context) {

        this(context, null);

    }

    public Button(Context context, AttributeSet attrs) {

        this(context, attrs, com.android.internal.R.attr.buttonStyle);

    }

    public Button(Context context, AttributeSet attrs, int defStyle) {

        super(context, attrs, defStyle);

    }

    @Override

    public void onInitializeAccessibilityEvent(AccessibilityEvent event) {

        super.onInitializeAccessibilityEvent(event);

        event.setClassName(Button. class.getName());

    }

    @Override

    public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {

        super.onInitializeAccessibilityNodeInfo(info);

        info.setClassName(Button. class.getName());

    }

}

是直接继承于TextView，所不同的是在构造方法中添加了Button的样式，并且在初始化可见性方面交由Button类自己来处理。虽然Button的实现比较简单，但是它的子类并不是这样。看一下：

直接子类只有有一个，CompoundButton。它是一个抽象类，而实现这个类的控件正是CheckBox, RadioButton, Switch, ToggleButton这四个，所以先重点说一下它。源码如下：

/**
*
* A button with two states, checked and unchecked. When the button is pressed
* or clicked, the state changes automatically.
*
*
* XML attributes
*
* 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}
*
*/
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 ;
}
/**
* Changes the checked state of this button.
*
* @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();
}
}

/**

 * <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();

    }

}

先从构造方法开始，在构造方法中，

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 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();

    }

先是从attrs中读取定义的属性，一个是Drawable用于设置背景；一个是布尔类型变量用于判断是否check过。设置背景使用的是setButtonDrawable()方法，代码如下：

/**
* 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();
}

/**

     * 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();

    }

这个方法写的就比较完善，可以作为一个学习的典范。首先判断传递过来的Drawable是否为空，如果不为空并且默认的Drawable也不为空，那么取消默认Drawable的callback，然后调用unscheduleDrawable方法。这个方法代码如下：

/**
* Unschedule any events associated with the given Drawable. This can be
* used when selecting a new Drawable into a view, so that the previous
* one is completely unscheduled.
*
* @param who The Drawable to unschedule.
*
* @see #drawableStateChanged
*/
public void unscheduleDrawable(Drawable who) {
if (mAttachInfo != null && who != null) {
mAttachInfo.mViewRootImpl .mChoreographer.removeCallbacks(
Choreographer.CALLBACK_ANIMATION, null, who);
}
}

 /**

     * Unschedule any events associated with the given Drawable.  This can be

     * used when selecting a new Drawable into a view, so that the previous

     * one is completely unscheduled.

     *

     * @param who The Drawable to unschedule.

     *

     * @see #drawableStateChanged

     */

    public void unscheduleDrawable(Drawable who) {

        if (mAttachInfo != null && who != null) {

            mAttachInfo.mViewRootImpl .mChoreographer.removeCallbacks(

                    Choreographer.CALLBACK_ANIMATION, null, who);

        }

    }

从方法注释中可以看出它的用途，正是更换Drawable时候使用的。接下来开始重新设置Drawable，包括回调、可见性、最小高度。最后调用refreshDrawableState()方法，这个是View类的方法，用于更新Drawable状态。

然后再回过头看一下setChecked(checked)方法，这个用于设置check，也就是button的点击状态。代码如下：

/**
* Changes the checked state of this button.
*
* @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 ;
}
}

/**

     * <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 ;

        }

    }

在这个方法中多出了一个接口，这个接口真是check的一个回调接口，代码如下：

/**
* 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);
}

/**

     * 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);

    }

这种回调接口在Android中处处可见，之前的文章也有介绍过。但是在上面的方法，它使用了一个mBroadcasting变量，进而巧妙地避免了重复递归的问题，大家自己感受一下。

然后就是ondraw()方法了，把之前的drawable画出来。代码如下：

@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 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);

        }

    }

看得出来，在onDrawable()方法中，最主要的部分还是如何确定上下左右四个参数。确定完后就可以画出来了。但是，CompoundButton是一个抽象类，并不能直接使用，那看一下它的子类是如何实现的：

1、CheckBox

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());
}
}

 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());

    }

}

和Button的实现差不多，使用了一个自己的样式。并且也是重写了那两个方法。再来看一下RadioButton，

public class RadioButton extends CompoundButton {
public RadioButton(Context context) {
this(context, null);
}
public RadioButton(Context context, AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.radioButtonStyle);
}
public RadioButton(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
/**
* {@inheritDoc}
*
* If the radio button is already checked, this method will not toggle the radio button.
*/
@Override
public void toggle() {
// we override to prevent toggle when the radio is already
// checked (as opposed to check boxes widgets)
if (!isChecked()) {
super.toggle();
}
}
@Override
public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(event);
event.setClassName(RadioButton. class.getName());
}
@Override
public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
super.onInitializeAccessibilityNodeInfo(info);
info.setClassName(RadioButton. class.getName());
}
}

public class RadioButton extends CompoundButton {

    public RadioButton(Context context) {

        this(context, null);

    }

    public RadioButton(Context context, AttributeSet attrs) {

        this(context, attrs, com.android.internal.R.attr.radioButtonStyle);

    }

    public RadioButton(Context context, AttributeSet attrs, int defStyle) {

        super(context, attrs, defStyle);

    }

    /**

     * {@inheritDoc}

     * <p>

     * If the radio button is already checked, this method will not toggle the radio button.

     */

    @Override

    public void toggle() {

        // we override to prevent toggle when the radio is already

        // checked (as opposed to check boxes widgets)

        if (!isChecked()) {

            super.toggle();

        }

    }

    @Override

    public void onInitializeAccessibilityEvent(AccessibilityEvent event) {

        super.onInitializeAccessibilityEvent(event);

        event.setClassName(RadioButton. class.getName());

    }

    @Override

    public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {

        super.onInitializeAccessibilityNodeInfo(info);

        info.setClassName(RadioButton. class.getName());

    }

}

和CheckBox实现差不多，区别在于多重写了一个方法，用于防止按钮被重复点击。另外还有ToggleButton以及Switch，前者实现也比较简单，后者稍微麻烦了一些，感兴趣可以自己分析。

最后切入正题，看看滑动Button要如何实现呢？首先看一下效果图：

图1-1

图1-2

图1-1所示的滑动Button实现的思路是这样的，背景图片有开和关的文字，一个按钮在其上面左右滑动，遮住相应的部分，使其在一个位置时候只能看到一个开关。

如图1-3，在实现的时候，先画一个开关背景图片只，然后在其上面画一个按钮，滑动开关的时候对上面的按钮进行处理即可。

准备：

1、按钮图片

2、背景图片

编码：

在自定义滑动按钮控件的时候，可以有多种选择，可以继承于Button，也可以继承于Button的子类，也可以继承于View类等。我们知道滑动按钮是一个很简单的控件，就是左右滑动改变显示内容，不需要其他的额外东西在里面，所以直接继承于View来实现即可。如果继承于系统的一些控件，那么有很多东西用不到，会造成浪费。

1、定义一个类继承于View，初始化构造方法，在构造方法中加载图片及其信息。

2、重写onMeasure()方法，计算控件的大小。

3、重写onTouchEvent()方法，对滑动事件进行判别处理。

4、定义接口，实现回调。

5、重写onDraw()方法，动态画出按钮。

代码如下：

/**
*
*/
package com.kince.slidebutton;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
/**
* @author kince
* @category 左右手势滑动button
* @serial 1.0.0
* @since 2014.5.17
* @see http://blog.csdn.net/wangjinyu501
*
*/
public class SlideButton extends View {
private Bitmap slideBitMap;// 滑动图片
private Bitmap switchBitMap;// 背景图片
private int slideBitMapWidth;// 滑动图片宽度
private int switchBitMapWidth;// 背景图片宽度
private int switchBitMapHeight;// 背景图片高度
private boolean currentState;// 开关状态
private boolean isSliding = false; // 是否正在滑动中
private int currentX; // 当前开关的位置
private OnToggleStateChangedListener mChangedListener;// 回调接口
/**
* @param context
* 在java代码中直接调用使用此构造方法
*/
public SlideButton(Context context) {
this(context, null);
// TODO Auto-generated constructor stub
}
/**
* @param context
* @param attrs
* 在xml中使用要用到这个方法
*/
public SlideButton(Context context, AttributeSet attrs) {
this(context, attrs, 0);
// TODO Auto-generated constructor stub
}
/**
* @param context
* @param attrs
* @param defStyleAttr
* 指定一个样式
*/
public SlideButton(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
initBitmap();
}
/**
* @category 加载背景图片以及开关图片然后获取各自的宽高
*
*/
private void initBitmap() {
// TODO Auto-generated method stub
slideBitMap = BitmapFactory.decodeResource(getResources(),
R.drawable.slide_button_background);
switchBitMap = BitmapFactory.decodeResource(getResources(),
R.drawable.switch_background);
slideBitMapWidth = slideBitMap.getWidth();
switchBitMapWidth = switchBitMap.getWidth();
switchBitMapHeight = switchBitMap.getHeight();
Log.i("switchBitMapWidth", switchBitMapWidth + "");
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// TODO Auto-generated method stub
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
setMeasuredDimension(switchBitMapWidth, switchBitMapHeight);// 设置控件的宽高
}
@Override
protected void onDraw(Canvas canvas) {
// 绘制button背景图片
canvas.drawBitmap(switchBitMap, 0, 0, null);
// 绘制滑动开关
if (isSliding) {// 如果当前状态是滑动中则动态绘制开关
int dis = currentX - slideBitMapWidth / 2;
if (dis < 0) {
dis = 0;
} else if (dis > switchBitMapWidth - slideBitMapWidth) {
dis = switchBitMapWidth - slideBitMapWidth;
}
canvas.drawBitmap(slideBitMap, dis, 0, null);
} else {
if (currentState) { // 绘制开关为开的状态
canvas.drawBitmap(slideBitMap, switchBitMapWidth
- slideBitMapWidth, 0, null);
} else { // 绘制开关为关的状态
canvas.drawBitmap(slideBitMap, 0, 0, null);
}
}
super.onDraw(canvas);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
// 手势识别判断滑动方向
int action = event.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
isSliding = true;
currentX = (int) event.getX();
break;
case MotionEvent.ACTION_MOVE:
currentX = (int) event.getX();
Log.i("currentX", currentX + "");
break;
case MotionEvent.ACTION_UP:
isSliding = false;
int bgCenter = switchBitMapWidth / 2;
boolean state = currentX > bgCenter; // 改变后的状态
if (state != currentState && mChangedListener != null) {// 添加回调
mChangedListener.onToggleStateChanged(state);
}
currentState = state;
break;
default:
break;
}
invalidate();
return true;
}
public OnToggleStateChangedListener getmChangedListener() {
return mChangedListener;
}
public void setmChangedListener(
OnToggleStateChangedListener mChangedListener) {
this.mChangedListener = mChangedListener;
}
public boolean isToggleState() {
return currentState;
}
public void setToggleState(boolean currentState) {
this.currentState = currentState;
}
}

/**

*

*/

package com.kince.slidebutton;

import android.content.Context;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.graphics.Canvas;

import android.util.AttributeSet;

import android.util.Log;

import android.view.MotionEvent;

import android.view.View;

/**

* @author kince

* @category 左右手势滑动button

* @serial 1.0.0

* @since 2014.5.17

* @see http://blog.csdn.net/wangjinyu501

*

*/

public class SlideButton extends View {

     private Bitmap slideBitMap;// 滑动图片

     private Bitmap switchBitMap;// 背景图片

     private int slideBitMapWidth;// 滑动图片宽度

     private int switchBitMapWidth;// 背景图片宽度

     private int switchBitMapHeight;// 背景图片高度

     private boolean currentState;// 开关状态

     private boolean isSliding = false; // 是否正在滑动中

     private int currentX; // 当前开关的位置

     private OnToggleStateChangedListener mChangedListener;// 回调接口

     /**

     * @param context

     *            在java代码中直接调用使用此构造方法

     */

     public SlideButton(Context context) {

          this(context, null);

          // TODO Auto-generated constructor stub

     }

     /**

     * @param context

     * @param attrs

     *            在xml中使用要用到这个方法

     */

     public SlideButton(Context context, AttributeSet attrs) {

          this(context, attrs, 0);

          // TODO Auto-generated constructor stub

     }

     /**

     * @param context

     * @param attrs

     * @param defStyleAttr

     *            指定一个样式

     */

     public SlideButton(Context context, AttributeSet attrs, int defStyleAttr) {

          super(context, attrs, defStyleAttr);

          initBitmap();

     }

     /**

     * @category 加载背景图片以及开关图片 然后获取各自的宽高

     *

     */

     private void initBitmap() {

          // TODO Auto-generated method stub

          slideBitMap = BitmapFactory.decodeResource(getResources(),

                    R.drawable.slide_button_background);

          switchBitMap = BitmapFactory.decodeResource(getResources(),

                    R.drawable.switch_background);

          slideBitMapWidth = slideBitMap.getWidth();

          switchBitMapWidth = switchBitMap.getWidth();

          switchBitMapHeight = switchBitMap.getHeight();

          Log.i("switchBitMapWidth", switchBitMapWidth + "");

     }

     @Override

     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

          // TODO Auto-generated method stub

          super.onMeasure(widthMeasureSpec, heightMeasureSpec);

          setMeasuredDimension(switchBitMapWidth, switchBitMapHeight);// 设置控件的宽高

     }

     @Override

     protected void onDraw(Canvas canvas) {

          // 绘制button背景图片

          canvas.drawBitmap(switchBitMap, 0, 0, null);

          // 绘制滑动开关

          if (isSliding) {// 如果当前状态是滑动中 则动态绘制开关

               int dis = currentX - slideBitMapWidth / 2;

               if (dis < 0) {

                    dis = 0;

               } else if (dis > switchBitMapWidth - slideBitMapWidth) {

                    dis = switchBitMapWidth - slideBitMapWidth;

               }

               canvas.drawBitmap(slideBitMap, dis, 0, null);

          } else {

               if (currentState) { // 绘制开关为开的状态

                    canvas.drawBitmap(slideBitMap, switchBitMapWidth

                              - slideBitMapWidth, 0, null);

               } else { // 绘制开关为关的状态

                    canvas.drawBitmap(slideBitMap, 0, 0, null);

               }

          }

          super.onDraw(canvas);

     }

     @Override

     public boolean onTouchEvent(MotionEvent event) {

          // 手势识别 判断滑动方向

          int action = event.getAction();

          switch (action) {

          case MotionEvent.ACTION_DOWN:

               isSliding = true;

               currentX = (int) event.getX();

               break;

          case MotionEvent.ACTION_MOVE:

               currentX = (int) event.getX();

               Log.i("currentX", currentX + "");

               break;

          case MotionEvent.ACTION_UP:

               isSliding = false;

               int bgCenter = switchBitMapWidth / 2;

               boolean state = currentX > bgCenter; // 改变后的状态

               if (state != currentState && mChangedListener != null) {// 添加回调

                    mChangedListener.onToggleStateChanged(state);

               }

               currentState = state;

               break;

          default:

               break;

          }

          invalidate();

          return true;

     }

     public OnToggleStateChangedListener getmChangedListener() {

          return mChangedListener;

     }

     public void setmChangedListener(

               OnToggleStateChangedListener mChangedListener) {

          this.mChangedListener = mChangedListener;

     }

     public boolean isToggleState() {

          return currentState;

     }

     public void setToggleState(boolean currentState) {

          this.currentState = currentState;

     }

}

回调接口，

package com.kince.slidebutton;
**
* @author kince
*
*/
ublic interface OnToggleStateChangedListener {
/**
* @category
* @param state
*/
public void onToggleStateChanged(boolean state);

  package com.kince.slidebutton;

/**

 * @author kince

 *

 */

public interface OnToggleStateChangedListener {

     /**

      * @category

      * @param state

      */

     public void onToggleStateChanged(boolean state);

}

Activity代码，

package com.kince.slidebutton;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;
import android.os.Build;
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment implements
OnToggleStateChangedListener {
private SlideButton slidebutton;
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
slidebutton = (SlideButton) rootView.findViewById(R.id.slidebutton1);
// 设置一下开关的状态
slidebutton.setToggleState(true); // 设置开关的状态为打开
slidebutton.setmChangedListener(this);
return rootView;
}
@Override
public void onToggleStateChanged(boolean state) {
// TODO Auto-generated method stub
FragmentActivity activity = getActivity();
if (state) {
Toast.makeText(activity, "开关打开", 0).show();
} else {
Toast.makeText(activity, "开关关闭", 0).show();
}
}
}
}

package com.kince.slidebutton;

import android.support.v7.app.ActionBarActivity;

import android.support.v7.app.ActionBar;

import android.support.v4.app.Fragment;

import android.support.v4.app.FragmentActivity;

import android.os.Bundle;

import android.view.LayoutInflater;

import android.view.Menu;

import android.view.MenuItem;

import android.view.View;

import android.view.ViewGroup;

import android.widget.Toast;

import android.os.Build;

public class MainActivity extends ActionBarActivity {

     @Override

     protected void onCreate(Bundle savedInstanceState) {

          super.onCreate(savedInstanceState);

          setContentView(R.layout.activity_main);

          if (savedInstanceState == null) {

               getSupportFragmentManager().beginTransaction()

                         .add(R.id.container, new PlaceholderFragment()).commit();

          }

     }

     @Override

     public boolean onCreateOptionsMenu(Menu menu) {

          // Inflate the menu; this adds items to the action bar if it is present.

          getMenuInflater().inflate(R.menu.main, menu);

          return true;

     }

     @Override

     public boolean onOptionsItemSelected(MenuItem item) {

          // Handle action bar item clicks here. The action bar will

          // automatically handle clicks on the Home/Up button, so long

          // as you specify a parent activity in AndroidManifest.xml.

          int id = item.getItemId();

          if (id == R.id.action_settings) {

               return true;

          }

          return super.onOptionsItemSelected(item);

     }

     /**

     * A placeholder fragment containing a simple view.

     */

     public static class PlaceholderFragment extends Fragment implements

               OnToggleStateChangedListener {

          private SlideButton slidebutton;

          public PlaceholderFragment() {

          }

          @Override

          public View onCreateView(LayoutInflater inflater, ViewGroup container,

                    Bundle savedInstanceState) {

               View rootView = inflater.inflate(R.layout.fragment_main, container,

                         false);

               slidebutton = (SlideButton) rootView.findViewById(R.id.slidebutton1);

               // 设置一下开关的状态

               slidebutton.setToggleState(true); // 设置开关的状态为打开

               slidebutton.setmChangedListener(this);

               return rootView;

          }

          @Override

          public void onToggleStateChanged(boolean state) {

               // TODO Auto-generated method stub

               FragmentActivity activity = getActivity();

               if (state) {

                    Toast.makeText(activity, "开关打开", 0).show();

               } else {

                    Toast.makeText(activity, "开关关闭", 0).show();

               }

          }

     }

}

未完待续。

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