/**
     * This method is invoked right before an action within this module is executed.
     * 该方法是当前模块的Action执行前调用的方法，将会触发[[EVENT_BEFORE_ACTION]]事件
     *
     * The method will trigger the [[EVENT_BEFORE_ACTION]] event. The return value of the method
     * will determine whether the action should continue to run.
     * 如果返回true，Action方法才会执行，否则终止执行
     *
     * In case the action should not run, the request should be handled inside of the `beforeAction` code
     * by either providing the necessary output or redirecting the request. Otherwise the response will be empty.
     *
     * If you override this method, your code should look like the following:
     * 如果要重写该方法，代码格式如下：
     *
     * ```php
     * public function beforeAction($action)
     * {
     *     if (!parent::beforeAction($action)) {//先要判断父类的beforeAction方法执行结果
     *         return false;
     *     }
     *
     *     // your custom code here
     *
     *     return true; // or false to not run the action
     * }
     * ```
     *
     * @param Action $action the action to be executed.
     * @return boolean whether the action should continue to be executed.
     */
    public function beforeAction($action)
    {
        $event = new ActionEvent($action);//实例化ActionEvent()
        $this->trigger(self::EVENT_BEFORE_ACTION, $event);//触发beforeAction事件
        return $event->isValid;//返回结果
    }

    /**
     * This method is invoked right after an action within this module is executed.
     * 该方法是当前模块的Action执行后调用的方法，将会触发[[EVENT_AFTER_ACTION]]事件
     * The method will trigger the [[EVENT_AFTER_ACTION]] event. The return value of the method
     * will be used as the action return value.
     * 如果返回true，后面的代码才会继续执行，否则终止执行
     *
     * If you override this method, your code should look like the following:
     * 如果要重写该方法，代码格式如下：
     *
     * ```php
     * public function afterAction($action, $result)
     * {
     *     $result = parent::afterAction($action, $result);//先要判断父类的afterAction方法执行结果
     *     // your custom code here
     *     return $result;
     * }
     * ```
     *
     * @param Action $action the action just executed.
     * @param mixed $result the action return result.
     * @return mixed the processed action result.
     */
    public function afterAction($action, $result)
    {
        $event = new ActionEvent($action);//实例化ActionEvent()
        $event->result = $result;//将Action方法的执行结果赋值给result常量
        $this->trigger(self::EVENT_AFTER_ACTION, $event);//触发beforeAction事件
        return $event->result;//返回结果
    }