PHP-Thinkphp-微信NATIVE支付不能生成二维码

namespace app\home\controller;




use think\Controller;

class Qcode extends Controller {

    /**
     * 生成二维码
     */
    public function index() {
        import('pay.weixin.example.phpqrcode.phpqrcode', EXTEND_PATH);
        $url = urldecode($_GET["data"]);
        ob_end_clean();//清空（擦除）缓冲区并关闭输出缓冲
        if(substr($url, 0, 6) == "weixin"){
            \QRcode::png($url);
        }else{
            header('HTTP/1.1 404 Not Found');
        }
    }
}

之前一直不能生成二维码，清空缓冲区就可以了

ob_end_clean();//清空（擦除）缓冲区并关闭输出缓冲