请问绑定 trigger 事件的代码在哪里？ [ 求助交流 ]

try {
    $this->state = self::STATE_BEFORE_REQUEST;
    $this->trigger(self::EVENT_BEFORE_REQUEST);

    $this->state = self::STATE_HANDLING_REQUEST;
    $response = $this->handleRequest($this->getRequest());

    $this->state = self::STATE_AFTER_REQUEST;
    $this->trigger(self::EVENT_AFTER_REQUEST);

    $this->state = self::STATE_SENDING_RESPONSE;
    $response->send();

    $this->state = self::STATE_END;

    return $response->exitStatus;

} catch (ExitException $e) {

    $this->end($e->statusCode, isset($response) ? $response : null);
    return $e->statusCode;

}

在上边这段代码中，我只看到了触发事件的地方，但是没有看到绑定这两个事件的地方，应该是先绑定，然后再触发，想问问各位绑定上边两个trigger事件的代码在哪里，我找了半天没有找到