Android应用中是怎么判断程序是在前台运行还是在后台运行的

public static boolean Frontdesk(Context context) {
 ActivityManager activityManager = (ActivityManager) context
   .getSystemService(Context.ACTIVITY_SERVICE);
 List<ActivityManager.RunningAppProcessInfo> appProcesses = activityManager
   .getRunningAppProcesses();
 for (ActivityManager.RunningAppProcessInfo appProcess : appProcesses) {
  if (appProcess.processName.equals(context.getPackageName())) {
   Log.i(context.getPackageName(), "此appimportace ="
     + appProcess.importance
     + ",context.getClass().getName()="
     + context.getClass().getName());
   if (appProcess.importance != ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND) {
    Log.i(context.getPackageName(), "处于后台"
      + appProcess.processName);
    return true;
   } else {
    Log.i(context.getPackageName(), "处于前台"
      + appProcess.processName);
    return false;
   }
  }
 }
 return false;
}