How to generate QR code in yii2

php composer.phar require "2amigos/yii2-qrcode-helper" "*"

"2amigos/yii2-qrcode-helper" : "*"

'2amigos/yii2-qrcode-helper' => 
   array (
    'name' => '2amigos/yii2-qrcode-helper',
    'version' => '1.0.2.0',
    'alias' => 
    array (
     '@dosamigos/qrcode' => $vendorDir . '/2amigos/yii2-qrcode-helper/src',
    ),
 ),

use dosamigos\qrcode\QrCode;  //引入类
\\ ... 
public function actionQrcode() 
{ 
  return QrCode::png('http://www.yii-china.com');  //调用二维码生成方法
}
public function actionDemo()
{
  return $this->render('index');
}

<img src="<?= Url::to([&#39;index/qrcode&#39;])?>" />