如何在Android界面中实现一个回弹效果

public class MyScrollView extends ScrollView {  private View childView;  public MyScrollView(Context context) {    super(context);  }  public MyScrollView(Context context, AttributeSet attrs) {    super(context, attrs);  }  public MyScrollView(Context context, AttributeSet attrs, int defStyleAttr) {    super(context, attrs, defStyleAttr);  }//  @Override//  protected void onLayout(boolean changed, int l, int t, int r, int b) {//    super.onLayout(changed, l, t, r, b);//  }  //获取子视图  @Override  protected void onFinishInflate() {    super.onFinishInflate();    if (getChildCount() > 0) {      childView = getChildAt(0);    }  }  private int lastY;//上一次y轴方向操作的坐标位置  private Rect normal = new Rect();//用于记录临界状态的左、上、右、下  private boolean isFinishAnimation = true;//是否动画结束  private int lastX, downX, downY;  //拦截:实现父视图对子视图的拦截  //是否拦截成功，取决于方法的返回值。返回值true:拦截成功。反之，拦截失败  @Override  public boolean onInterceptTouchEvent(MotionEvent ev) {    boolean isIntercept = false;    int eventX = (int) ev.getX();    int eventY = (int) ev.getY();    switch (ev.getAction()) {      case MotionEvent.ACTION_DOWN:        lastX = downX = eventX;        lastY = downY = eventY;        break;      case MotionEvent.ACTION_MOVE:        //获取水平和垂直方向的移动距离        int absX = Math.abs(eventX - downX);        int absY = Math.abs(eventY - downY);        if(absY > absX && absY >= UIUtils.dp2px(10)){          isIntercept = true;//执行拦截        }        lastX = eventX;        lastY = eventY;        break;    }    return isIntercept;  }  @Override  public boolean onTouchEvent(MotionEvent ev) {    if (childView == null || !isFinishAnimation) {      return super.onTouchEvent(ev);    }    int eventY = (int) ev.getY();//获取当前的y轴坐标    switch (ev.getAction()) {      case MotionEvent.ACTION_DOWN:        lastY = eventY;        break;      case MotionEvent.ACTION_MOVE:        int dy = eventY - lastY;//微小的移动量        if (isNeedMove()) {          if (normal.isEmpty()) {            //记录了childView的临界状态的左、上、右、下            normal.set(childView.getLeft(), childView.getTop(), childView.getRight(), childView.getBottom());          }          //重新布局          childView.layout(childView.getLeft(), childView.getTop() + dy / 2, childView.getRight(), childView.getBottom() + dy / 2);        }        lastY = eventY;//重新赋值        break;      case MotionEvent.ACTION_UP:        if (isNeedAnimation()) {          //使用平移动画          int translateY = childView.getBottom() - normal.bottom;          TranslateAnimation translateAnimation = new TranslateAnimation(0, 0, 0, -translateY);          translateAnimation.setDuration(200);//        translateAnimation.setFillAfter(true);//停留在最终位置上          translateAnimation.setAnimationListener(new Animation.AnimationListener() {            @Override            public void onAnimationStart(Animation animation) {              isFinishAnimation = false;            }            @Override            public void onAnimationEnd(Animation animation) {              isFinishAnimation = true;              childView.clearAnimation();//清除动画              //重新布局              childView.layout(normal.left, normal.top, normal.right, normal.bottom);              //清除normal的数据              normal.setEmpty();            }            @Override            public void onAnimationRepeat(Animation animation) {            }          });          //启动动画          childView.startAnimation(translateAnimation);        }        break;    }    return super.onTouchEvent(ev);  }  //判断是否需要执行平移动画  private boolean isNeedAnimation() {    return !normal.isEmpty();  }  private boolean isNeedMove() {    int childMeasuredHeight = childView.getMeasuredHeight();//获取子视图的高度    int scrollViewMeasuredHeight = this.getMeasuredHeight();//获取布局的高度    Log.e("TAG", "childMeasuredHeight = " + childMeasuredHeight);    Log.e("TAG", "scrollViewMeasuredHeight = " + scrollViewMeasuredHeight);    int dy = childMeasuredHeight - scrollViewMeasuredHeight;//dy >= 0    int scrollY = this.getScrollY();//获取用户在y轴方向上的偏移量 （上 + 下 -）    if (scrollY <= 0 || scrollY >= dy) {      return true;//按照我们自定义的MyScrollView的方式处理    }    //其他处在临界范围内的，返回false。即表示，仍按照ScrollView的方式处理    return false;  }}