Yii Restful. Exception "setting Unknown Property" When Try To Override Action In Activecontroller

I am learning implementing restful web service using Yii2. In following controller, I am trying to override the ‘index’ action. But I encountered following error. Anyone can give me some clue? Thanks.

Unknown Property – yii\base\UnknownPropertyException

Setting unknown property: api\modules\v1\controllers\CountryController::checkAccess




<?php


namespace api\modules\v1\controllers;


use yii\data\ActiveDataProvider;

use yii\rest\ActiveController;


class CountryController extends ActiveController

{

    public $modelClass = 'api\modules\v1\models\Country';


    public $serializer = [

        'class' => 'yii\rest\Serializer',

        'collectionEnvelope' => 'items',

    ];


    //-- disable, override or add actions

    //-- when overriding default action, make sure current controller has checkAccess() method implemented

    public function actions()

    {

        $actions = parent::actions();

        //-- override default actions with actions in this controller

        $actions['index'] = [

            'class' => $this->className(),

            'modelClass' => $this->modelClass,

            'checkAccess' => [$this, 'checkAccess'],

        ];

        return $actions;

    }


    public function actionIndex()

    {

        return new ActiveDataProvider(['query' => Country::find()]);

    }


    public function checkAccess($action, $model = null, $params = [])

    {

        //--check if the user can access $action & $model

        //--throw ForbiddenHttpException if access should be denied


        return true;

    }

}