如何 判斷程序是在 前臺 還是 後臺運行？

如何 判斷程序是在 前臺 還是 後臺運行？

下面是我在網上找到的

         ActivityManager activityManager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
           List<RunningAppProcessInfo> appProcesses = activityManager.getRunningAppProcesses();
           for (RunningAppProcessInfo appProcess : appProcesses) {
                if (appProcess.processName.equals( getPackageName() ) ) {
                       if (appProcess.importance == RunningAppProcessInfo.IMPORTANCE_BACKGROUND) {
                       
                       
                        Toast.makeText(RecorderActivity.this, "後臺!", Toast.LENGTH_SHORT).show();
                       
                        
                           
                         
                       }else{
        
                       
                         
                         Toast.makeText(RecorderActivity.this, "前臺!", Toast.LENGTH_SHORT).show();    
                                 
                       }
                  }
                
           };   爲什麼 按了 HOME鍵後 ，  程序已經去了後臺，爲什麼 還是 顯示 “前臺” ？？