Android 实现ViewPager边界回弹效果实例代码

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; }}