PopupWindow指定显示位置以及背景透明的全套解决方案

 private void showPopUp(View v) {
       LinearLayout layout = new LinearLayout(this);
       layout.setBackgroundColor(Color.WHITE);
       TextView tv = new TextView(this);
       tv.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 200));
       tv.setText("xxxxx");
       tv.setTextColor(Color.RED);
       layout.addView(tv);
//通过改变当前activity的window属性来控制
       WindowManager.LayoutParams lp = getWindow()
               .getAttributes();
       lp.alpha = 0.4f;
       getWindow().addFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);
       getWindow().setAttributes(lp);
       PopupWindow popupWindow = new PopupWindow(layout, 120, 120);
       popupWindow.setFocusable(true);
       popupWindow.setOutsideTouchable(true);
       popupWindow.setBackgroundDrawable(new BitmapDrawable());
       int[] location = new int[2];
       v.getLocationOnScreen(location);
       popupWindow.setBackgroundDrawable(null);
       popupWindow.showAtLocation(v, Gravity.NO_GRAVITY, location[0], location[1] + popupWindow.getHeight() + 20);
       popupWindow.setOnDismissListener(new PopupWindow.OnDismissListener() {
           @Override
           public void onDismiss() {
    //此时记得也调用一下哦
               WindowManager.LayoutParams lp = getWindow()
                       .getAttributes();
               lp.alpha = 1f;
               getWindow().addFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);
               getWindow().setAttributes(lp);
           }
       });
       popupWindow.update();
   }