RunningAppProcessInfo Sınıfı

pkgList Alanı
Şöyle yaparız

ActivityManager activityManager = (ActivityManager) getSystemService(ACTIVITY_SERVICE);
List<RunningAppProcessInfo> appProcesses= activityManager.getRunningAppProcesses();

for (RunningAppProcessInfo appProcess : appProcesses) {

  PackageInfo p = null;
  try {
    p = this.getPackageManager().getPackageInfo(appProcess.pkgList[0],
 PackageManager.GET_PERMISSIONS);
  } catch (NameNotFoundException e) {
     e.printStackTrace();
  }

  if(p != null && p.packageName.equals(getPackageName()) &&
     appProcess.importance == RunningAppProcessInfo.IMPORTANCE_FOREGROUND){
    Log.d("Is in background:", "false");
    return false;
  }
}
Log.d("Is in background:", "true");