public function actionModifyActivity()
 {
     $request = yii::$app->request;
     $activityId = $request->post('activityId');
     $activity = Activity::findActivityById($activityId);
     $activity['peoplenum'] = intval($request->post('peoplenum'));
     $activity->save();
     $attendUsers = User::findActivityAttendUsers($activityId);
     return $this->render("oneActivity", ['activity' => $activity, 'attendUsers' => $attendUsers]);
 }