ios – 如何围绕sourceRect的角落来寻找Peek和Pop 3D Touch？

以下是使用可压缩UILabel的示例：

class ViewController: UIViewController {

    var previewingContext: UIViewControllerPreviewing?
    let label = UILabel(frame: CGRectMake(150,250,100,50))

    override func viewDidLoad() {
        super.viewDidLoad()

        let BACkground = UIImageView(frame: view.bounds)
        BACkground.image = UIImage(named: "image.jpg")
        view.addSubview(BACkground)

        label.BACkgroundColor = UIColor.whiteColor()
        label.text = "Press me!"
        label.textAlignment = .Center
        label.layer.cornerRadius = 20
        label.clipsToBounds = true
        label.userInteractionEnabled = true
        view.addSubview(label)

        previewingContext = registerForPreviewingWithDelegate(self,sourceView: label)
    }
}

extension ViewController: UIViewControllerPreviewingDelegate {

    func previewingContext(previewingContext: UIViewControllerPreviewing,viewControllerForLOCATIOn LOCATIOn: CGPoint) -> UIViewController? {
        previewingContext.sourceRect = label.bounds

        return UIViewController()
    }

    func previewingContext(previewingContext: UIViewControllerPreviewing,commitViewController viewControllerToCommit: UIViewController) {
        showViewController(viewControllerToCommit,sender: self)
    }
}