如何在Swift 3.0中拖放子画面？

class DraggableView: UIView {
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupView()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setupView()
    }
    
    private func setupView() {
        // 添加视图的样式和内容
        backgroundColor = UIColor.blue
    }
}

class ViewController: UIViewController {
    var draggableView: DraggableView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建拖放手势识别器
        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(handlePan(_:)))
        
        // 创建子视图
        draggableView = DraggableView(frame: CGRect(x: 100, y: 100, width: 100, height: 100))
        draggableView.addGestureRecognizer(panGesture)
        
        // 将子视图添加到视图控制器的视图中
        view.addSubview(draggableView)
    }
    
    @objc func handlePan(_ gesture: UIPanGestureRecognizer) {
        let translation = gesture.translation(in: view)
        
        // 移动子视图的位置
        draggableView.center = CGPoint(x: draggableView.center.x + translation.x, y: draggableView.center.y + translation.y)
        
        // 重置手势的位移
        gesture.setTranslation(CGPoint.zero, in: view)
    }
}