android仿QQ个人主页下拉回弹效果

/***
  * @param topView
  * @param imgResId 图片id
  */
 public void setTopView(View topView, int imgResId) {
  if (null != topView) {
   this.topView = topView;
   imageView = (ImageView) topView.findViewById(imgResId);
  }
 }

ACTION_DOWN:
  case MotionEvent.ACTION_DOWN:
    startY = ev.getRawY();
    if (!hadInit) {//初始化，只要初始化一次就够了
     childAt0Top = getChildAt(0).getTop();
     ivInitHeight = imageView.getHeight();
     hadInit = true;
    }
    break;

case MotionEvent.ACTION_MOVE:
    Log.d(TAG, "dy = " + dy);
    dy = ev.getRawY() - startY;
    if (dy > 0 && 0 == getFirstVisiblePosition() && 
    childAt0Top == getChildAt(0).getTop()) {//(1)手指从上往下拉：下拉
     int tempDy = (int) (dy + 0.5);
     //一定也要给topView增加一定的高度，否则从上啦到下拉就不会显示
     imageView.getLayoutParams().height = imageView.getHeight() + tempDy;
     topView.getLayoutParams().height = topView.getHeight() + tempDy;
     topView.requestLayout();
     isChangedHeight = true;

    } else {//(2)手指从下往上拉：上拉
     int tempDy = (int) (dy - 0.5);
     int currHeight = imageView.getHeight();
     float translatiOnY= getNegativeMaxValue(tempDy, -currHeight, 0);
     if (translationY <= 0 && currHeight > 0) {
      LinearLayout.LayoutParams lp = 
      (LinearLayout.LayoutParams) topView.getLayoutParams();
      //一定要减去titleBar，如果没有去掉Winow.xxx.Title,还要减去这个高度，否则会显示不全
      lp.height = topView.getHeight() + (int) translationY;
      topView.requestLayout();//
      isChangedHeight = true;
     }
    }
    //用这个getRawY而不是用getY，是因为listview也会随着改变，
    //而getY获取的就是listview本身的Y,所以基本是变化不大的，
    // 而使用getRawY相对于屏幕的距离，保证滑动了多大的距离就改变多大的距离
    startY = ev.getRawY();
    break;

 float translatiOnY= getNegativeMaxValue(tempDy, -currHeight, 0);
 /***
  * 手指上移过程dy是负数
  * 返回负数最大值：0是最大值，不可以超过
  *
  * @param value   移动的最终距离：上次的位置+当次移动的偏移量之和，就是本次要移动的最终的偏移量
  * @param canMoveMaxValue 可移动的最大值
  * @param maxValue
  * @return
  */
 public static float getNegativeMaxValue(float value,float canMoveMaxValue, float maxValue) {
  return Math.min(maxValue, Math.max(canMoveMaxValue, value));
 }

case MotionEvent.ACTION_OUTSIDE:
   case MotionEvent.ACTION_CANCEL:
   case MotionEvent.ACTION_UP:
    if (isChangedHeight) {
     if (imageView.getHeight() > ivInitHeight) {// (1)手指从上往下拉：下拉
      ResetAnimation resetAnimation = 
      new ResetAnimation(ivInitHeight, imageView, topView);
      resetAnimation.setDuration(200);
      imageView.startAnimation(resetAnimation);
     } else {//(2)手指从下往上拉：上拉。。。这个不用处理。。。因为上拉后松开让其topview固定

     }
     isChangedHeight = false;
    }
    break;

 /**
  * 自定义回弹动画，使imageView和topView过渡回弹到初始位置
  */
 static class ResetAnimation extends Animation {
  private View topView;
  private int topCurrHeight;

  private ImageView ivStretch;
  private int ivInitHeight;
  private int ivCurrHeight;

  public ResetAnimation(int ivInitHeiht, ImageView ivStretch, View topView) {

   this.ivInitHeight = ivInitHeiht;
   this.ivCurrHeight = ivStretch.getHeight();
   this.topCurrHeight = topView.getHeight();
   this.ivStretch = ivStretch;
   this.topView = topView;
  }

  @Override
  protected void applyTransformation(float interpolatedTime, Transformation t) {
   int dy = (int) ((ivCurrHeight - ivInitHeight) * interpolatedTime);
   Log.d(TAG, "anim dy = " + dy);
   ivStretch.getLayoutParams().height = ivCurrHeight - dy;
   topView.getLayoutParams().height = topCurrHeight - dy;
   topView.requestLayout();
  }
 }

/***
  * 这个方法是在滑出屏幕时回调，但是由于android系统国内厂商修改的面目全非，有些机型是不会回调的，比如vivo
  * 所以不要使用这个方法搞事情
  *
  * @param scrollX
  * @param scrollY
  */
 @Override
 protected boolean overScrollBy(int deltaX, int deltaY, int scrollX, int scrollY, 
 int scrollRangeX, int scrollRangeY, int maxOverScrollX, int maxOverScrollY, 
 boolean isTouchEvent) {
  Log.d(TAG, "deltax = " + deltaX + " deltaY = " + deltaY);
  return super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX,
   scrollRangeY, maxOverScrollX, maxOverScrollY, isTouchEvent);
 }