关于yii2:yii2问题

1.Yii2 验证码不显示

} else {
        ob_clean();  //Add this line, can solve this problem. Or add in other suitable places
        $this->setHttpHeaders();
        Yii::$app->response->format = Response::FORMAT_RAW;
        return $this->renderImage($this->getVerifyCode());
    }