android popupWindow 背景遮罩设置最佳方式

设置popupwindow的高度是 wrap_parent

重写 showAsDropDown 方法，设置window的背景透明度

@Override
    public void showAsDropDown(View anchor) {
        if (activity != null && !activity.isFinishing()) {
            Window dialogWindow = activity.getWindow();
            WindowManager.LayoutParams lp = dialogWindow.getAttributes(); // 获取对话框当前的参数值
            lp.width = WindowManager.LayoutParams.MATCH_PARENT;
            lp.height = WindowManager.LayoutParams.MATCH_PARENT;
            lp.alpha = 0.7f;
            dialogWindow.setAttributes(lp);
        }
        super.showAsDropDown(anchor);
    }

重写 dismiss 方法，恢复window的背景透明度

@Override
    public void dismiss() {
        if (activity != null && !activity.isFinishing()) {
            Window dialogWindow = activity.getWindow();
            WindowManager.LayoutParams lp = dialogWindow.getAttributes(); // 获取对话框当前的参数值
            lp.width = WindowManager.LayoutParams.MATCH_PARENT;
            lp.height = WindowManager.LayoutParams.MATCH_PARENT;
            lp.alpha = 1.0f;
            dialogWindow.setAttributes(lp);
        }

        super.dismiss();
    }

注意 super方法要在 改变透明度的后面
否则会把你的壁纸给 闪出来