Android根据手势顶部View自动展示与隐藏效果

 @Override
   public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
    Log.i(tag, "onScroll -> distanceY" + distanceY);
    if (distanceY <0) {// 手势向下滑动是负值
     animatorLayoutOffset(1);
    }
    if (distanceY > 0) {
     animatorLayoutOffset(0f);
    }
    return true;
   }

 @Override
 protected void onFinishInflate() {
  super.onFinishInflate();
  viewTop = findViewById(R.id.group_top);
  viewBottom = findViewById(R.id.group_bottom);
 }

@Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  int width = MeasureSpec.getSize(widthMeasureSpec);
  int height = MeasureSpec.getSize(heightMeasureSpec);
  viewTop.measure(MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY), MeasureSpec.makeMeasureSpec(height, MeasureSpec.AT_MOST));
  viewBottom.measure(MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY), MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY));
  setMeasuredDimension(width, height);
 }
 @Override
 protected void onLayout(boolean changed, int l, int t, int r, int b) {
  int topHeight = viewTop.getMeasuredHeight();
  float offset = layoutOffset * topHeight;
  int width = r - l;
  float topViewYTop = offset - topHeight;
  float topViewYBottom = topViewYTop + topHeight;
  viewTop.layout(0, (int) topViewYTop, width, (int) topViewYBottom);
  viewBottom.layout(0, (int) topViewYBottom, width, (int) topViewYBottom + viewBottom.getMeasuredHeight());
 }
 private void animatorLayoutOffset(float offset) {
  if (animator != null && animator.isRunning()) {
   return;
  }
  animator = ObjectAnimator.ofFloat(this, "layoutOffset", layoutOffset, offset);
  animator.setDuration(500);
  animator.start();
 }