Android--实现ViewPager边界回弹效果(转)

该View转自   http://blog.csdn.net/Kalwang/article/details/4708721  ，感谢这位大神。

 public class BounceBackViewPager extends ViewPager {

     private int currentPosition = 0;
     private Rect mRect = new Rect();//用来记录初始位置
     private boolean handleDefault = true;
     private float preX = 0f;
     private static final float RATIO = 0.5f;//摩擦系数
     private static final float SCROLL_WIDTH = 10f;

     public BounceBackViewPager(Context context) {
         super(context);
     }

     public BounceBackViewPager(Context context, AttributeSet attrs) {
         super(context, attrs);
     }

     @Override
     public boolean dispatchKeyEvent(KeyEvent event) {
         return super.dispatchKeyEvent(event);
     }

     @Override
     public boolean onInterceptTouchEvent(MotionEvent ev) {
         if (ev.getAction() == MotionEvent.ACTION_DOWN) {
             preX = ev.getX();//记录起点
             currentPosition = getCurrentItem();
         }
         return super.onInterceptTouchEvent(ev);
     }

     @Override
     public boolean onTouchEvent(MotionEvent ev) {
         switch (ev.getAction()) {
             case MotionEvent.ACTION_UP:
                 onTouchActionUp();
                 break;
             case MotionEvent.ACTION_MOVE:
                 if (getAdapter().getCount() == 1) {
                     float nowX = ev.getX();
                     float offset = nowX - preX;
                     preX = nowX;

                     if (offset > SCROLL_WIDTH) {//手指滑动的距离大于设定值
                         whetherConditionIsRight(offset);
                     } else if (offset < -SCROLL_WIDTH) {
                         whetherConditionIsRight(offset);
                     } else if (!handleDefault) {//这种情况是已经出现缓冲区域了，手指慢慢恢复的情况
                         if (getLeft() + (int) (offset * RATIO) != mRect.left) {
                             layout(getLeft() + (int) (offset * RATIO), getTop(), getRight() + (int) (offset * RATIO), getBottom());
                         }
                     }
                 } else if ((currentPosition == 0 || currentPosition == getAdapter().getCount() - 1)) {
                     float nowX = ev.getX();
                     float offset = nowX - preX;
                     preX = nowX;

                     if (currentPosition == 0) {
                         if (offset > SCROLL_WIDTH) {//手指滑动的距离大于设定值
                             whetherConditionIsRight(offset);
                         } else if (!handleDefault) {//这种情况是已经出现缓冲区域了，手指慢慢恢复的情况
                             if (getLeft() + (int) (offset * RATIO) >= mRect.left) {
                                 layout(getLeft() + (int) (offset * RATIO), getTop(), getRight() + (int) (offset * RATIO), getBottom());
                             }
                         }
                     } else {
                         if (offset < -SCROLL_WIDTH) {
                             whetherConditionIsRight(offset);
                         } else if (!handleDefault) {
                             if (getRight() + (int) (offset * RATIO) <= mRect.right) {
                                 layout(getLeft() + (int) (offset * RATIO), getTop(), getRight() + (int) (offset * RATIO), getBottom());
                             }
                         }
                     }
                 } else {
                     handleDefault = true;
                 }

                 if (!handleDefault) {
                     return true;
                 }
                 break;

             default:
                 break;
         }
         return super.onTouchEvent(ev);
     }

     private void whetherConditionIsRight(float offset) {
         if (mRect.isEmpty()) {
             mRect.set(getLeft(), getTop(), getRight(), getBottom());
         }
         handleDefault = false;
         layout(getLeft() + (int) (offset * RATIO), getTop(), getRight() + (int) (offset * RATIO), getBottom());
     }

     private void onTouchActionUp() {
         if (!mRect.isEmpty()) {
             recoveryPosition();
         }
     }

     private void recoveryPosition() {
         TranslateAnimation ta = new TranslateAnimation(getLeft(), mRect.left, 0, 0);
         ta.setDuration(300);
         startAnimation(ta);
         layout(mRect.left, mRect.top, mRect.right, mRect.bottom);
         mRect.setEmpty();
         handleDefault = true;
     }

 }