Swift ClipToBounds适用于Tap手势

Question

我创建了一个按钮来添加UIImageView作为UIView（命名为backgroundView）的子视图，然后我希望所有UIImageViews都可以在UIView中拖动（但不能从它中拖出），所以我使用“backgroundView.cliptobounds = true“但它不起作用。

那么如何在添加子视图后通过按钮添加子视图，我可以在父UIView的范围内拖动子视图？

class ViewController: UIViewController {

@IBOutlet weak var addSubview: UIButton!

@IBOutlet weak var backgroundView: UIView!


override func viewDidLoad() {
    super.viewDidLoad()
    backgroundView.clipsToBounds = true

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


@IBAction func buttonAddSubview(sender: AnyObject) {
    let labelText = sender.titleLabel!?.text!
    var subview : UIImageView
    subview  = UIImageView(frame:CGRectMake(300, 300, 200, 200));
    subview = UIImageView(image: UIImage(named: labelText!))


    backgroundView.addSubview(subview)
    backgroundView.clipsToBounds = true

    subview.image = UIImage(named:labelText!)
    }

}