[Android] background application can know what the application currently running in the foreground

這是個一個舊時代的產物，超過 Android 4.4 (API 19) 以上有另一個寫法，小於等於 4.4 請服用：

ActivityManager am = (ActivityManager) AppService.this.getSystemService(ACTIVITY_SERVICE);
// The first in the list of RunningTasks is always the foreground task.
RunningTaskInfo foregroundTaskInfo = am.getRunningTasks(1).get(0);

String foregroundTaskPackageName = foregroundTaskInfo .topActivity.getPackageName();
PackageManager pm = AppService.this.getPackageManager();
PackageInfo foregroundAppPackageInfo = pm.getPackageInfo(foregroundTaskPackageName, 0);
String foregroundTaskAppName = foregroundAppPackageInfo.applicationInfo.loadLabel(pm).toString();

<uses-permission android:name="android.permission.GET_TASKS" />

基於上面的例子，加強版如下：

Something like,

class ForegroundCheckTask extends AsyncTask<Context, Void, Boolean> {

  @Override
  protected Boolean doInBackground(Context... params) {
    final Context context = params[0].getApplicationContext();
    return isAppOnForeground(context);
  }

  private boolean isAppOnForeground(Context context) {
    ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
    List<RunningAppProcessInfo> appProcesses = activityManager.getRunningAppProcesses();
    if (appProcesses == null) {
      return false;
    }
    final String packageName = context.getPackageName();
    for (RunningAppProcessInfo appProcess : appProcesses) {
      if (appProcess.importance == RunningAppProcessInfo.IMPORTANCE_FOREGROUND && appProcess.processName.equals(packageName)) {
        return true;
      }
    }
    return false;
  }
}

// Use like this:
boolean foregroud = new ForegroundCheckTask().execute(context).get();

以上是判斷自己的APP 有沒有在前景。

增加判斷 IMPORTANCE_VISIBLE 也沒什麼用…

The neatest and not deprecated way that I’ve found so far to do this, as follows:

@Override
public boolean foregrounded() {
    ActivityManager.RunningAppProcessInfo appProcessInfo = new ActivityManager.RunningAppProcessInfo();
    ActivityManager.getMyMemoryState(appProcessInfo);
    return (appProcessInfo.importance == IMPORTANCE_FOREGROUND || appProcessInfo.importance == IMPORTANCE_VISIBLE)
}

It only works with SDK 16+.

EDIT:

I removed the following code from the solution:

KeyguardManager km = (KeyguardManager) getSystemService(Context.KEYGUARD_SERVICE);
// App is foreground, but screen is locked, so show notification
return km.inKeyguardRestrictedInputMode();

since that makes not getting the notifications if the screen locked. I had a look to the framework and the purpose of this is not entirely clear. I’d remove it. Checking the process info state would be enough 🙂

最後是透過 的方法取得正確的前景App:

ActivityManager am = (ActivityManager)context.getSystemService(Context.ACTIVITY_SERVICE);
ComponentName cn = am.getRunningTasks(1).get(0).topActivity;
String currentPackageName = cn.getPackageName();