对话框弹窗给后面的acitvity加背景遮罩

/**
* 设置添加屏幕的背景透明度；1表示透明，0.0表示纯黑
*
* @param bgAlpha
*/
public static void backgroundAlpha(float bgAlpha, Activity activity) {
WindowManager.LayoutParams lp = activity.getWindow().getAttributes();
activity.getWindow().addFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);
lp.alpha = bgAlpha; //0.0-1.0
activity.getWindow().setAttributes(lp);
}