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]);
}