android 如何判断程序是否在前台运行

 private boolean isTopActivity(){
         List<RunningTaskInfo>  tasksInfo = activityManager.getRunningTasks(1);
         if(tasksInfo.size() > 0){
             //应用程序位于堆栈的顶层
             if(packageName.equals(tasksInfo.get(0).topActivity.getPackageName())){
                 return true;
             }
         }
         return false;
     }