最近用7.0的android手机测试项目，发现popwindow的showAsDropDown失效了,
不过最终找到了两种解决方案:
1、重写showAsDropDown方法:

@Override
     public void showAsDropDown(View anchor) {
          if(Build.VERSION.SDK_INT == 24) {
            Rect rect = new Rect();
            anchor.getGlobalVisibleRect(rect);
            int h = anchor.getResources().getDisplayMetrics().heightPixels - rect.bottom;
            setHeight(h);
          }
        super.showAsDropDown(anchor);
  }

2、使用showAtLocation方法:

  if (Build.VERSION.SDK_INT >= 24) {
            int[] point = new int[2];
            v.getLocationInWindow(point);
            mPopWindow.showAtLocation(((Activity) mContext).getWindow().getDecorView(), Gravity.NO_GRAVITY, 0, point[1] + v.getHeight());
        } else {
            mPopWindow.showAsDropDown(v);
        }