Android 滑动效果

转自:http://blog.csdn.net/sunboy_2050/article/details/7483176

感谢原作者.

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自定义控件，较常用View、ViewGroup、Scroller三个类，其继承关系如下：

 

 

本示例自定义控件，实现一个Gallery效果，并添加了一个显示View个数和位置的bar条，效果图：

 

 

自定义控件，包含通过继承实现的自定义控件和自定义控件属性两部分，即控件和属性

1、自定义属性

自定义属性，分为定义属性、解析属性、设置属性三部分，具体步骤：

首先，在res/valus/attrs.xml属性资源文件中，定义控件属性

1. <?xml version="1.0" encoding="utf-8"?>  
2. <resources>  
3.     <declare-styleable name="com.myapps.widget.Pager">  
4.         <attr name="pageWidth" format="dimension" />  
5.     </declare-styleable>  
6.     <declare-styleable name="com.myapps.widget.PagerBar">  
7.         <attr name="barColor" format="color" />  
8.         <attr name="highlightColor" format="color" />  
9.         <attr name="fadeDelay" format="integer" />  
10.         <attr name="fadeDuration" format="integer" />  
11.         <attr name="roundRectRadius" format="dimension" />  
12.     </declare-styleable>  
13. </resources>  

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="com.myapps.widget.Pager">
        <attr name="pageWidth" format="dimension" />
    </declare-styleable>
    
    <declare-styleable name="com.myapps.widget.PagerBar">
        <attr name="barColor" format="color" />
        <attr name="highlightColor" format="color" />
        <attr name="fadeDelay" format="integer" />
        <attr name="fadeDuration" format="integer" />
        <attr name="roundRectRadius" format="dimension" />
    </declare-styleable>
</resources>

然后，在自定义控件的代码中，解析自定义的属性，如在PagerBar.java：

1. // 自定义属性  
2.         TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.com_myapps_widget_PagerBar);  
3.         int barBackColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_barColor, DEFAULT_BAR_BACKCOLOR);              // bar背景色  
4.         int barForeColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_highlightColor, DEFAULT_BAR_FORECOLOR);    // bar前景色  
5.         fadeDelay = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDelay, DEFAULT_FADE_DELAY);             // bar消失延迟时间  
6.         fadeDuration = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDuration, DEFAULT_FADE_DURATION);    // bar消失动画时间  
7.         ovalRadius = a.getDimension(R.styleable.com_myapps_widget_PagerBar_roundRectRadius, 2f);  
8.         a.recycle();  

// 自定义属性
		TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.com_myapps_widget_PagerBar);
		int barBackColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_barColor, DEFAULT_BAR_BACKCOLOR);				// bar背景色
		int barForeColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_highlightColor, DEFAULT_BAR_FORECOLOR);	// bar前景色
		fadeDelay = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDelay, DEFAULT_FADE_DELAY);				// bar消失延迟时间
		fadeDuration = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDuration, DEFAULT_FADE_DURATION);	// bar消失动画时间
		ovalRadius = a.getDimension(R.styleable.com_myapps_widget_PagerBar_roundRectRadius, 2f);
		a.recycle();

最后，在布局文件中设置属性，如在main.xml

1. <com.homer.mycontrol.PagerBar  
2.     android:id="@+id/control"  
3.     android:layout_width="fill_parent"  
4.     android:layout_height="4dip"  
5.     android:layout_margin="8dip"  
6.     myapps:roundRectRadius="2dip" />  <!-- 自定义圆角 -->  

    <com.homer.mycontrol.PagerBar
        android:id="@+id/control"
        android:layout_width="fill_parent"
        android:layout_height="4dip"
        android:layout_margin="8dip"
        myapps:roundRectRadius="2dip" />	 <!-- 自定义圆角 -->

其中，在布局中间main.xml中，需要注意：

xmlns:myapps="http://schemas.android.com/apk/res/com.homer.mycontrol"

定义属性时，在declare-styleable的name中，需要包含com.myapps.widget.PagerBar，表示自定义的控件PageBar是widget子类，myapps是xmlns解析标记

解析属性时，在TypedArray中，需要包含R.styleable.com_myapps_widget_PagerBar，横线替换了圆点.

定义属性时，在com.homer.mycontrol.PagerBar中，需要包含myapps:roundRectRadius="2dip"，加上myapps解析标记

2、自定义控件PagerBar

自定义PagerBar，在图片下方用来显示图片滑到了第几页，即上面效果图（图2、图3）中的下部银白色细条，具体实现：

1. public PagerBar(Context context, AttributeSet attrs, int defStyle) {  
2.     super(context, attrs, defStyle);  
3.     // 自定义属性  
4.     TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.com_myapps_widget_PagerBar);  
5.     int barBackColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_barColor, DEFAULT_BAR_BACKCOLOR);              // bar背景色  
6.     int barForeColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_highlightColor, DEFAULT_BAR_FORECOLOR);    // bar前景色  
7.     fadeDelay = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDelay, DEFAULT_FADE_DELAY);             // bar消失延迟时间  
8.     fadeDuration = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDuration, DEFAULT_FADE_DURATION);    // bar消失动画时间  
9.     ovalRadius = a.getDimension(R.styleable.com_myapps_widget_PagerBar_roundRectRadius, 2f);  
10.     a.recycle();  
11.     barBackPaint = new Paint();  
12.     barBackPaint.setColor(barBackColor);  
13.     barForePaint = new Paint();  
14.     barForePaint.setColor(barForeColor);  
15.     fadeOutAnimation = new AlphaAnimation(1f, 0f);  
16.     fadeOutAnimation.setDuration(fadeDuration);  
17.     fadeOutAnimation.setRepeatCount(0);  
18.     fadeOutAnimation.setInterpolator(new LinearInterpolator());  
19.     fadeOutAnimation.setFillEnabled(true);  
20.     fadeOutAnimation.setFillAfter(true);  
21. public int getNumPages() {  
22.     return numPages;  
23. public void setNumPages(int numPages) {  
24.     if (numPages <= 0) {  
25.         throw new IllegalArgumentException("numPages must be positive");  
26.     this.numPages = numPages;  
27.     invalidate();       // 重绘View  
28.     fadeOut();          // 设置bar消失效果  
29. /** bar消失动画 */  
30. private void fadeOut() {  
31.     if (fadeDuration > 0) {  
32.         clearAnimation();  
33.         fadeOutAnimation.setStartTime(AnimationUtils.currentAnimationTimeMillis() + fadeDelay); //延迟fadeDelay后动画开始  
34.         setAnimation(fadeOutAnimation);  
35. /**  @return  0 to numPages-1 */  
36. public int getCurrentPage() {  
37.     return currentPage;  
38. /** @param currentPage  0 to numPages-1  */  
39. public void setCurrentPage(int currentPage) {  
40.     if (currentPage < 0 || currentPage >= numPages) {  
41.         throw new IllegalArgumentException("currentPage parameter out of bounds");  
42.     if (this.currentPage != currentPage) {  
43.         this.currentPage = currentPage;  
44.         this.position = currentPage * getPageWidth();   // bar前景色滑动条的起始位置（像素值）  
45.         invalidate();  
46.         fadeOut();  
47. /** 获取View的宽度，即bar的宽度 */  
48. public int getPageWidth() {  
49.     return getWidth() / numPages;   // getWidth()是PagerBar的宽度（减去了margin左右距离后）  
50. /**  @param position     can be -pageWidth to pageWidth*(numPages+1)  */  
51. public void setPosition(int position) {  
52.     if (this.position != position) {  
53.         this.position = position;  
54.         invalidate();  
55.         fadeOut();  
56. @Override  
57. protected void onDraw(Canvas canvas) {  
58.     canvas.drawRoundRect(new RectF(0, 0, getWidth(), getHeight()), ovalRadius, ovalRadius, barBackPaint);   // 绘制bar背景  
59.     canvas.drawRoundRect(new RectF(position, 0, position + (getWidth() / numPages), getHeight()), ovalRadius, ovalRadius, barForePaint);    // 绘制bar前景  

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

		// 自定义属性
		TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.com_myapps_widget_PagerBar);
		int barBackColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_barColor, DEFAULT_BAR_BACKCOLOR);				// bar背景色
		int barForeColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_highlightColor, DEFAULT_BAR_FORECOLOR);	// bar前景色
		fadeDelay = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDelay, DEFAULT_FADE_DELAY);				// bar消失延迟时间
		fadeDuration = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDuration, DEFAULT_FADE_DURATION);	// bar消失动画时间
		ovalRadius = a.getDimension(R.styleable.com_myapps_widget_PagerBar_roundRectRadius, 2f);
		a.recycle();

		barBackPaint = new Paint();
		barBackPaint.setColor(barBackColor);

		barForePaint = new Paint();
		barForePaint.setColor(barForeColor);

		fadeOutAnimation = new AlphaAnimation(1f, 0f);
		fadeOutAnimation.setDuration(fadeDuration);
		fadeOutAnimation.setRepeatCount(0);
		fadeOutAnimation.setInterpolator(new LinearInterpolator());
		fadeOutAnimation.setFillEnabled(true);
		fadeOutAnimation.setFillAfter(true);
	}

	public int getNumPages() {
		return numPages;
	}

	public void setNumPages(int numPages) {
		if (numPages <= 0) {
			throw new IllegalArgumentException("numPages must be positive");
		}
		this.numPages = numPages;
		invalidate();		// 重绘View
		fadeOut();			// 设置bar消失效果
	}

	/** bar消失动画 */
	private void fadeOut() {
		if (fadeDuration > 0) {
			clearAnimation();
			fadeOutAnimation.setStartTime(AnimationUtils.currentAnimationTimeMillis() + fadeDelay);	//延迟fadeDelay后动画开始
			setAnimation(fadeOutAnimation);
		}
	}

	/**  @return  0 to numPages-1 */
	public int getCurrentPage() {
		return currentPage;
	}

	/** @param currentPage  0 to numPages-1  */
	public void setCurrentPage(int currentPage) {
		if (currentPage < 0 || currentPage >= numPages) {
			throw new IllegalArgumentException("currentPage parameter out of bounds");
		}
		if (this.currentPage != currentPage) {
			this.currentPage = currentPage;
			this.position = currentPage * getPageWidth();	// bar前景色滑动条的起始位置（像素值）
			invalidate();
			fadeOut();
		}
	}

	/** 获取View的宽度，即bar的宽度 */
	public int getPageWidth() {
		return getWidth() / numPages;	// getWidth()是PagerBar的宽度（减去了margin左右距离后）
	}

	/**  @param position     can be -pageWidth to pageWidth*(numPages+1)  */
	public void setPosition(int position) {
		if (this.position != position) {
			this.position = position;
			invalidate();
			fadeOut();
		}
	}

	@Override
	protected void onDraw(Canvas canvas) {
		canvas.drawRoundRect(new RectF(0, 0, getWidth(), getHeight()), ovalRadius, ovalRadius, barBackPaint);	// 绘制bar背景
		canvas.drawRoundRect(new RectF(position, 0, position + (getWidth() / numPages), getHeight()), ovalRadius, ovalRadius, barForePaint);	// 绘制bar前景
	}
}

3、自定义控件Pager

自定义控件Pager，继承自ViewGroup，用来显示图片的，类似于Gallery，实现主要部分包含：

A、自定义属性解析

B、Pager容器控件Scroller滑动页设置与控制

C、容器状态保存（onSaveInstanceState）

D、容器事件监听接口

详细实现如下：

A、自定义属性解析

1. public Pager(Context context, AttributeSet attrs, int defStyle) {  
2.     super(context, attrs, defStyle);  
3.     // 自定义属性  
4.     TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.com_myapps_widget_Pager);  
5.     pageWidthSpec = a.getDimensionPixelSize(R.styleable.com_myapps_widget_Pager_pageWidth, SPEC_UNDEFINED);  
6.     a.recycle();  

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

		// 自定义属性
		TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.com_myapps_widget_Pager);
		pageWidthSpec = a.getDimensionPixelSize(R.styleable.com_myapps_widget_Pager_pageWidth, SPEC_UNDEFINED);
		a.recycle();
	}

B、Pager容器控件Scroller滑动页设置与控制

1. public void setCurrentPage(int currentPage) {  
2.     mCurrentPage = Math.max(0, Math.min(currentPage, getChildCount()));     // 非常好  
3.     scrollTo(getScrollXForPage(mCurrentPage), 0);  
4.     invalidate();   // 重绘View  
5. int getCurrentPage() {  
6.     return mCurrentPage;  
7. public void setPageWidth(int pageWidth) {  
8.     this.pageWidthSpec = pageWidth;  
9. public int getPageWidth() {  
10.     return pageWidth;  
11. /** 获取whichPage的Pager起始x位置，whichPage从0开始计 */  
12. private int getScrollXForPage(int whichPage) {  
13.     return (whichPage * pageWidth) - pageWidthPadding();  
14. /** 返回View的 paddingwidth 一半(1/2)*/  
15. int pageWidthPadding() {  
16.     return ((getMeasuredWidth() - pageWidth) / 2);  
17. @Override  
18. public void computeScroll() {       // update  mScrollX and mScrollY  of View  
19.     if (mScroller.computeScrollOffset()) {  
20.         scrollTo(mScroller.getCurrX(), mScroller.getCurrY());  
21.         postInvalidate();           // invalidate the View from a non-UI thread  
22.     } else if (mNextPage != INVALID_SCREEN) {  
23.         mCurrentPage = mNextPage;  
24.         mNextPage = INVALID_SCREEN;  
25.         clearChildrenCache();  
26. @Override  
27. protected void dispatchDraw(Canvas canvas) {    // draw the child views  
28.     final long drawingTime = getDrawingTime();  // 绘制childView  
29.     final int count = getChildCount();  
30.     for (int i = 0; i < count; i++) {  
31.         drawChild(canvas, getChildAt(i), drawingTime);  
32.     for (OnScrollListener mListener : mListeners) { // 自定义接口  
33.         int adjustedScrollX = getScrollX() + pageWidthPadding();  
34.         mListener.onScroll(adjustedScrollX);  
35.         if (adjustedScrollX % pageWidth == 0) { // scroll finished  
36.             mListener.onViewScrollFinished(adjustedScrollX / pageWidth);  
37. @Override  
38. protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  
39.     super.onMeasure(widthMeasureSpec, heightMeasureSpec);  
40.     pageWidth = (pageWidthSpec == SPEC_UNDEFINED) ? getMeasuredWidth() : pageWidthSpec;  
41.     pageWidth = Math.min(pageWidth, getMeasuredWidth());  
42.     final int count = getChildCount();  
43.     for (int i = 0; i < count; i++) {  
44.         widthMeasureSpec = MeasureSpec.makeMeasureSpec(pageWidth, MeasureSpec.EXACTLY);  
45.         getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);  
46.     if (mFirstLayout) { // 第一次显示Pager时，page的位置  
47.         scrollTo(getScrollXForPage(mCurrentPage), mScroller.getCurrY());  
48.         mFirstLayout = false;  
49. @Override  
50. protected void onLayout(boolean changed, int left, int top, int right, int bottom) {  
51.     int childLeft = 0;  
52.     final int count = getChildCount();  // 绘制childView  
53.     for (int i = 0; i < count; i++) {  
54.         final View child = getChildAt(i);  
55.         if (child.getVisibility() != View.GONE) {  
56.             final int childWidth = child.getMeasuredWidth();  
57.             child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());  
58.             childLeft += childWidth;  

	public void setCurrentPage(int currentPage) {
		mCurrentPage = Math.max(0, Math.min(currentPage, getChildCount()));		// 非常好
		scrollTo(getScrollXForPage(mCurrentPage), 0);
		invalidate();	// 重绘View
	}

	int getCurrentPage() {
		return mCurrentPage;
	}

	public void setPageWidth(int pageWidth) {
		this.pageWidthSpec = pageWidth;
	}

	public int getPageWidth() {
		return pageWidth;
	}

	/** 获取whichPage的Pager起始x位置，whichPage从0开始计 */
	private int getScrollXForPage(int whichPage) {
		return (whichPage * pageWidth) - pageWidthPadding();
	}

	/** 返回View的 paddingwidth 一半(1/2)*/
	int pageWidthPadding() {
		return ((getMeasuredWidth() - pageWidth) / 2);
	}

	@Override
	public void computeScroll() {		// update  mScrollX and mScrollY  of View
		if (mScroller.computeScrollOffset()) {
			scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
			postInvalidate();			// invalidate the View from a non-UI thread
		} else if (mNextPage != INVALID_SCREEN) {
			mCurrentPage = mNextPage;
			mNextPage = INVALID_SCREEN;
			clearChildrenCache();
		}
	}

	@Override
	protected void dispatchDraw(Canvas canvas) {	// draw the child views
		
		final long drawingTime = getDrawingTime();	// 绘制childView
		final int count = getChildCount();
		for (int i = 0; i < count; i++) {
			drawChild(canvas, getChildAt(i), drawingTime);
		}

		for (OnScrollListener mListener : mListeners) {	// 自定义接口
			int adjustedScrollX = getScrollX() + pageWidthPadding();
			mListener.onScroll(adjustedScrollX);
			if (adjustedScrollX % pageWidth == 0) {	// scroll finished
				mListener.onViewScrollFinished(adjustedScrollX / pageWidth);
			}
		}
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);

		pageWidth = (pageWidthSpec == SPEC_UNDEFINED) ? getMeasuredWidth() : pageWidthSpec;
		pageWidth = Math.min(pageWidth, getMeasuredWidth());

		final int count = getChildCount();
		for (int i = 0; i < count; i++) {
			widthMeasureSpec = MeasureSpec.makeMeasureSpec(pageWidth, MeasureSpec.EXACTLY);
			getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
		}

		if (mFirstLayout) {	// 第一次显示Pager时，page的位置
			scrollTo(getScrollXForPage(mCurrentPage), mScroller.getCurrY());
			mFirstLayout = false;
		}
	}

	@Override
	protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
		int childLeft = 0;

		final int count = getChildCount();	// 绘制childView
		for (int i = 0; i < count; i++) {
			final View child = getChildAt(i);
			if (child.getVisibility() != View.GONE) {
				final int childWidth = child.getMeasuredWidth();
				child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
				childLeft += childWidth;
			}
		}
	}

1. @Override  
2. public boolean onInterceptTouchEvent(MotionEvent ev) {  
3.     final int action = ev.getAction();  
4.     if ((action == MotionEvent.ACTION_MOVE) && (mTouchState != TOUCH_STATE_REST)) { // 正在滑动中  
5.         return true;  
6.     final float x = ev.getX();  
7.     final float y = ev.getY();  
8.     switch (action) {  
9.     case MotionEvent.ACTION_MOVE:  
10.         if (mTouchState == TOUCH_STATE_REST) {  
11.             checkStartScroll(x, y);  
12.         break;  
13.     case MotionEvent.ACTION_DOWN:  
14.         mLastMotionX = x;  
15.         mLastMotionY = y;  
16.         mAllowLongPress = true;  
17.         mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;    // scroll 完成后，重置状态  
18.         break;  
19.     case MotionEvent.ACTION_CANCEL:  
20.     case MotionEvent.ACTION_UP:  
21.         clearChildrenCache();  
22.         mTouchState = TOUCH_STATE_REST;  
23.         break;  
24.     return mTouchState != TOUCH_STATE_REST;  
25. @Override  
26. public boolean onTouchEvent(MotionEvent ev) {  
27.     if (mVelocityTracker == null) {  
28.         mVelocityTracker = VelocityTracker.obtain();  
29.     mVelocityTracker.addMovement(ev);  
30.     final int action = ev.getAction();  
31.     final float x = ev.getX();  
32.     final float y = ev.getY();  
33.     switch (action) {  
34.     case MotionEvent.ACTION_DOWN:  
35.         if (!mScroller.isFinished()) {  
36.             mScroller.abortAnimation();  
37.         mLastMotionX = x;  
38.         break;  
39.     case MotionEvent.ACTION_MOVE:  
40.         if (mTouchState == TOUCH_STATE_REST) {  
41.             checkStartScroll(x, y);  
42.         } else if (mTouchState == TOUCH_STATE_SCROLLING) {  // scrolling 状态时，重绘view  
43.             int deltaX = (int) (mLastMotionX - x);  
44.             mLastMotionX = x;  
45.             if (getScrollX() < 0 || getScrollX() > getChildAt(getChildCount() - 1).getLeft()) {  
46.                 deltaX /= 2;  
47.             scrollBy(deltaX, 0);  
48.         break;  
49.     case MotionEvent.ACTION_UP:  
50.         if (mTouchState == TOUCH_STATE_SCROLLING) {  
51.             final VelocityTracker velocityTracker = mVelocityTracker;  
52.             velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);  
53.             int velocityX = (int) velocityTracker.getXVelocity();  
54.             if (velocityX > SNAP_VELOCITY && mCurrentPage > 0) {  
55.                 snapToPage(mCurrentPage - 1);  
56.             } else if (velocityX < -SNAP_VELOCITY && mCurrentPage < getChildCount() - 1) {  
57.                 snapToPage(mCurrentPage + 1);  
58.             } else {  
59.                 snapToDestination();  
60.             if (mVelocityTracker != null) {  
61.                 mVelocityTracker.recycle();  
62.                 mVelocityTracker = null;  
63.         mTouchState = TOUCH_STATE_REST;  
64.         break;  
65.     case MotionEvent.ACTION_CANCEL:  
66.         mTouchState = TOUCH_STATE_REST;  
67.     return true;  
68. /** 检查scroll状态，并设置绘制scroll缓存 */  
69. private void checkStartScroll(float x, float y) {  
70.     final int xDiff = (int) Math.abs(x - mLastMotionX);  
71.     final int yDiff = (int) Math.abs(y - mLastMotionY);  
72.     boolean xMoved = xDiff > mTouchSlop;  
73.     boolean yMoved = yDiff > mTouchSlop;  
74.     if (xMoved || yMoved) {  
75.         if (xMoved) {  
76.             mTouchState = TOUCH_STATE_SCROLLING;        // 设置为scrolling 状态  
77.             enableChildrenCache();  
78.         if (mAllowLongPress) {  
79.             mAllowLongPress = false;  
80.             final View currentScreen = getChildAt(mCurrentPage);  
81.             currentScreen.cancelLongPress();    // Cancels a pending long press  
82. void enableChildrenCache() {  
83.     setChildrenDrawingCacheEnabled(true);       // Enables or disables the drawing cache for each child of this viewGroup  
84.     setChildrenDrawnWithCacheEnabled(true); // Tells the ViewGroup to draw its children using their drawing cache  
85. void clearChildrenCache() {  
86.     setChildrenDrawnWithCacheEnabled(false);  
87. private void snapToDestination() {  
88.     final int startX = getScrollXForPage(mCurrentPage);  
89.     int whichPage = mCurrentPage;  
90.     if (getScrollX() < startX - getWidth() / 8) {  
91.         whichPage = Math.max(0, whichPage - 1);  
92.     } else if (getScrollX() > startX + getWidth() / 8) {  
93.         whichPage = Math.min(getChildCount() - 1, whichPage + 1);  
94.     snapToPage(whichPage);  
95. void snapToPage(int whichPage) {  
96.     enableChildrenCache();  
97.     boolean changingPages = whichPage != mCurrentPage;  
98.     mNextPage = whichPage;  
99.     View focusedChild = getFocusedChild();  
100.     if (focusedChild != null && changingPages && focusedChild == getChildAt(mCurrentPage)) {  
101.         focusedChild.clearFocus();  
102.     final int newX = getScrollXForPage(whichPage);  
103.     final int delta = newX - getScrollX();  
104.     mScroller.startScroll(getScrollX(), 0, delta, 0, Math.abs(delta) * 2);  
105.     invalidate();  
106. /** 向左滑动 */  
107. public void scrollLeft() {  
108.     if (mNextPage == INVALID_SCREEN && mCurrentPage > 0 && mScroller.isFinished()) {  
109.         snapToPage(mCurrentPage - 1);  
110. /** 向右滑动 */  
111. public void scrollRight() {  
112.     if (mNextPage == INVALID_SCREEN && mCurrentPage < getChildCount() - 1 && mScroller.isFinished()) {  
113.         snapToPage(mCurrentPage + 1);  

	@Override
	public boolean onInterceptTouchEvent(MotionEvent ev) {
		final int action = ev.getAction();
		if ((action == MotionEvent.ACTION_MOVE) && (mTouchState != TOUCH_STATE_REST)) {	// 正在滑动中
			return true;
		}

		final float x = ev.getX();
		final float y = ev.getY();

		switch (action) {
		case MotionEvent.ACTION_MOVE:
			if (mTouchState == TOUCH_STATE_REST) {
				checkStartScroll(x, y);
			}
			break;

		case MotionEvent.ACTION_DOWN:
			mLastMotionX = x;
			mLastMotionY = y;
			mAllowLongPress = true;

			mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;	// scroll 完成后，重置状态
			break;

		case MotionEvent.ACTION_CANCEL:
		case MotionEvent.ACTION_UP:
			clearChildrenCache();
			mTouchState = TOUCH_STATE_REST;
			break;
		}

		return mTouchState != TOUCH_STATE_REST;
	}

	@Override
	public boolean onTouchEvent(MotionEvent ev) {
		if (mVelocityTracker == null) {
			mVelocityTracker = VelocityTracker.obtain();
		}
		mVelocityTracker.addMovement(ev);

		final int action = ev.getAction();
		final float x = ev.getX();
		final float y = ev.getY();

		switch (action) {
		case MotionEvent.ACTION_DOWN:
			if (!mScroller.isFinished()) {
				mScroller.abortAnimation();
			}
			mLastMotionX = x;
			break;
			
		case MotionEvent.ACTION_MOVE:
			if (mTouchState == TOUCH_STATE_REST) {
				checkStartScroll(x, y);
			} else if (mTouchState == TOUCH_STATE_SCROLLING) {	// scrolling 状态时，重绘view
				int deltaX = (int) (mLastMotionX - x);
				mLastMotionX = x;

				if (getScrollX() < 0 || getScrollX() > getChildAt(getChildCount() - 1).getLeft()) {
					deltaX /= 2;
				}
				scrollBy(deltaX, 0);
			}
			break;
			
		case MotionEvent.ACTION_UP:
			if (mTouchState == TOUCH_STATE_SCROLLING) {
				final VelocityTracker velocityTracker = mVelocityTracker;
				velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
				int velocityX = (int) velocityTracker.getXVelocity();

				if (velocityX > SNAP_VELOCITY && mCurrentPage > 0) {
					snapToPage(mCurrentPage - 1);
				} else if (velocityX < -SNAP_VELOCITY && mCurrentPage < getChildCount() - 1) {
					snapToPage(mCurrentPage + 1);
				} else {
					snapToDestination();
				}

				if (mVelocityTracker != null) {
					mVelocityTracker.recycle();
					mVelocityTracker = null;
				}
			}
			mTouchState = TOUCH_STATE_REST;
			break;
		case MotionEvent.ACTION_CANCEL:
			mTouchState = TOUCH_STATE_REST;
		}

		return true;
	}

	/** 检查scroll状态，并设置绘制scroll缓存 */
	private void checkStartScroll(float x, float y) {
		final int xDiff = (int) Math.abs(x - mLastMotionX);
		final int yDiff = (int) Math.abs(y - mLastMotionY);

		boolean xMoved = xDiff > mTouchSlop;
		boolean yMoved = yDiff > mTouchSlop;

		if (xMoved || yMoved) {
			if (xMoved) {
				mTouchState = TOUCH_STATE_SCROLLING;		// 设置为scrolling 状态
				enableChildrenCache();
			}
			if (mAllowLongPress) {
				mAllowLongPress = false;
				final View currentScreen = getChildAt(mCurrentPage);
				currentScreen.cancelLongPress();	// Cancels a pending long press
			}
		}
	}

	void enableChildrenCache() {
		setChildrenDrawingCacheEnabled(true);		// Enables or disables the drawing cache for each child of this viewGroup
		setChildrenDrawnWithCacheEnabled(true);	// Tells the ViewGroup to draw its children using their drawing cache
	}

	void clearChildrenCache() {
		setChildrenDrawnWithCacheEnabled(false);
	}

	private void snapToDestination() {
		final int startX = getScrollXForPage(mCurrentPage);
		int whichPage = mCurrentPage;
		if (getScrollX() < startX - getWidth() / 8) {
			whichPage = Math.max(0, whichPage - 1);
		} else if (getScrollX() > startX + getWidth() / 8) {
			whichPage = Math.min(getChildCount() - 1, whichPage + 1);
		}

		snapToPage(whichPage);
	}

	void snapToPage(int whichPage) {
		enableChildrenCache();

		boolean changingPages = whichPage != mCurrentPage;

		mNextPage = whichPage;

		View focusedChild = getFocusedChild();
		if (focusedChild != null && changingPages && focusedChild == getChildAt(mCurrentPage)) {
			focusedChild.clearFocus();
		}

		final int newX = getScrollXForPage(whichPage);
		final int delta = newX - getScrollX();
		mScroller.startScroll(getScrollX(), 0, delta, 0, Math.abs(delta) * 2);
		invalidate();
	}

	/** 向左滑动 */
	public void scrollLeft() {
		if (mNextPage == INVALID_SCREEN && mCurrentPage > 0 && mScroller.isFinished()) {
			snapToPage(mCurrentPage - 1);
		}
	}

	/** 向右滑动 */
	public void scrollRight() {
		if (mNextPage == INVALID_SCREEN && mCurrentPage < getChildCount() - 1 && mScroller.isFinished()) {
			snapToPage(mCurrentPage + 1);
		}
	}

C、容器状态保存（onSaveInstanceState）

1. /** 保存状态 */  
2. public static class SavedState extends BaseSavedState {  
3.     int currentScreen = -1;  
4.     SavedState(Parcelable superState) {  
5.         super(superState);  
6.     private SavedState(Parcel in) {  
7.         super(in);  
8.         currentScreen = in.readInt();  
9.     public static final Parcelable.Creator<SavedState> CREATOR = new Parcelable.Creator<SavedState>() {  
10.         public SavedState createFromParcel(Parcel in) { // get data written by Parcelable.writeToParcel()     
11.             return new SavedState(in);  
12.         public SavedState[] newArray(int size) {            // create  array of the Parcelable   
13.             return new SavedState[size];  
14.     @Override  
15.     public void writeToParcel(Parcel out, int flags) {      // set data to parcel  
16.         super.writeToParcel(out, flags);  
17.         out.writeInt(currentScreen);  
18. @Override  
19. protected Parcelable onSaveInstanceState() {        // 保存状态  
20.     final SavedState state = new SavedState(super.onSaveInstanceState());  
21.     state.currentScreen = mCurrentPage;     // save InstanceState  
22.     return state;  
23. @Override  
24. protected void onRestoreInstanceState(Parcelable state) {   // 恢复状态  
25.     SavedState savedState = (SavedState) state;  
26.     super.onRestoreInstanceState(savedState.getSuperState());   // get InstanceState  
27.     if (savedState.currentScreen != INVALID_SCREEN) {  
28.         mCurrentPage = savedState.currentScreen;      

	/** 保存状态 */
	public static class SavedState extends BaseSavedState {
		int currentScreen = -1;

		SavedState(Parcelable superState) {
			super(superState);
		}

		private SavedState(Parcel in) {
			super(in);
			currentScreen = in.readInt();
		}

		public static final Parcelable.Creator<SavedState> CREATOR = new Parcelable.Creator<SavedState>() {
			public SavedState createFromParcel(Parcel in) {	// get data written by Parcelable.writeToParcel()	
				return new SavedState(in);
			}

			public SavedState[] newArray(int size) {			// create  array of the Parcelable 
				return new SavedState[size];
			}
		};
		
		@Override
		public void writeToParcel(Parcel out, int flags) {		// set data to parcel
			super.writeToParcel(out, flags);
			out.writeInt(currentScreen);
		}

	}

	@Override
	protected Parcelable onSaveInstanceState() {		// 保存状态
		final SavedState state = new SavedState(super.onSaveInstanceState());
		state.currentScreen = mCurrentPage;	 	// save InstanceState
		return state;
	}

	@Override
	protected void onRestoreInstanceState(Parcelable state) {	// 恢复状态
		SavedState savedState = (SavedState) state;
		super.onRestoreInstanceState(savedState.getSuperState());	// get InstanceState
		if (savedState.currentScreen != INVALID_SCREEN) {
			mCurrentPage = savedState.currentScreen;	
		}
	}

D、容器事件监听接口

1. public void addOnScrollListener(OnScrollListener listener) {  
2.     mListeners.add(listener);  
3. public void removeOnScrollListener(OnScrollListener listener) {  
4.     mListeners.remove(listener);  
5. /** 自定义接口 */  
6. public static interface OnScrollListener {  
7.     void onScroll(int scrollX);  
8.     void onViewScrollFinished(int currentPage);  

	public void addOnScrollListener(OnScrollListener listener) {
		mListeners.add(listener);
	}

	public void removeOnScrollListener(OnScrollListener listener) {
		mListeners.remove(listener);
	}

	/** 自定义接口 */
	public static interface OnScrollListener {
		void onScroll(int scrollX);
		void onViewScrollFinished(int currentPage);
	}

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