I am trying this method but it is deprecated.
ActivityManager activityManager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
List<ActivityManager.RunningTaskInfo> tasks = activityManager.getRunningTasks(Integer.MAX_VALUE);
for (int i = 0; i < tasks.size(); i++) {
Log.e("Running task", "Running task: " + tasks.get(i).baseActivity.toShortString() + "\t\t ID: " + tasks.get(i).id);
}