protected function sendImageMsgToXmlString(WxSendImageMsg $msg)
    {
        $formatStr = <<<XML
<xml>
<ToUserName><![CDATA[%s]]></ToUserName>
<FromUserName><![CDATA[%s]]></FromUserName>
<CreateTime>%d</CreateTime>
<MsgType><![CDATA[%s]]></MsgType>
<Image>
<MediaId><![CDATA[%s]]></MediaId>
</Image>
</xml>
XML;
        $result = sprintf($formatStr,   $msg->getToUserName(),
                                        $msg->getFromUserName(),
                                        strtotime($msg->getCreateTime()),
                                        $msg->getMsgType(),
                                        $msg->getMediaId()
                        );


        return $result;
    }