UIActivityViewController更改位置

Question

我有一个像这样的UIActivityViewController：

let textToShare = "Swift is awesome!  Check out this website about it!"

        if let myWebsite = NSURL(string: "http://www.codingexplorer.com/") {
            let objectsToShare = [textToShare, myWebsite]
            let activityVC = UIActivityViewController(activityItems: objectsToShare, applicationActivities: nil)
            activityVC.excludedActivityTypes = [UIActivityTypeAddToReadingList]

            activityVC.popoverPresentationController?.sourceView = self.view

            self.presentViewController(activityVC, animated: true, completion: nil)
        }

如何更改位置？