如何仅通过电子邮件分享使用UIActivityViewController使用swift

 let activityViewController = UIActivityViewController (activityItems: contentArray, applicationActivities:nil)
        if let popoverController = activityViewController.popoverPresentationController {
            popoverController.sourceView = sender

        }
        self.presentViewController(activityViewController, animated: true, completion: nil)
 let activityViewController = UIActivityViewCon