/**
  * This method checks that weather the service is busy or not, which means id any task exist for
  * certain activity
  *
  * @param activityName name of activity, which will be checked
  * @return true for busy, false for not busy
  */
 public boolean isBusy(String activityName) {
   boolean ret = false;
   FileManagerActivityInfo activityInfo = mActivityMap.get(activityName);
   if (activityInfo == null) {
     LogUtils.w(TAG, "isBusy return false,because activityInfo is null!");
     return ret;
   }
   BaseAsyncTask task = activityInfo.getTask();
   if (task != null) {
     return task.isTaskBusy();
   }
   return false;
 }