将MMS发送到iOS 8中的通用设备

Question

我正在尝试以编程方式发送彩信。我按照这个问题和答案：how to send MMS from iPhone app

当翻译成Swift时，它看起来像这样：

@IBAction func sendMMSButtonPressed(sender: UIButton) {
        if !MFMessageComposeViewController.canSendText(){
            return
        }

        let phoneToCall = "sms"
        let phoneToCallEncoded = phoneToCall.stringByAddingPercentEscapesUsingEncoding(NSASCIIStringEncoding)
        let url = NSURL(string: phoneToCallEncoded!)!
        UIApplication.sharedApplication().openURL(url)

        let pasteboard = UIPasteboard.generalPasteboard()
        pasteboard.persistent = true
        pasteboard.image = UIImage(named: "slow")
        let messageController = MFMessageComposeViewController()
        messageController.messageComposeDelegate = self
        messageController.body = "What an awesome app"

        self.presentViewController(messageController, animated: true, completion: nil)

    }

问题是图像不会自动添加到消息中，因此我只发送短信而不是短信。发送图像的正确方法是什么？我不想使用iMessages，因为我希望用户能够将MMS发送到Android，Windows ...用户。谢谢你的帮助！