ios - 平移后将 View 返回到其原始位置

Question

我有一个可以平移的 View (鸡)，释放后应该返回到它的原始位置。现在，当 panGesture 结束时，小鸡就消失了。

这是我的代码:

override func viewDidLoad() {
        super.viewDidLoad()

        // record original Position
        originalChickenPosition = chicken.center
        print(originalChickenPosition) // works fine

        view.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: "handlePan:"))    
    }


    func handlePan(panGesture: UIPanGestureRecognizer){

        switch panGesture.state{

        case .Began:
            // start flying

        case .Changed:
            // follow the pan
            let dCenter = panGesture.translationInView(view)
            chicken.center = CGPointMake(chicken.center.x + dCenter.x, chicken.center.y + dCenter.y)
            panGesture.setTranslation(CGPointZero, inView: view)

        case .Ended:
            // fly back
            if originalChickenPosition != nil{
              chicken.center = originalChickenPosition!
            }

        default: break

        }   
    }

我发现了这个:Returning view to original position after pan gesture, swift但这似乎是一个不同的问题，如果我的观点能跳回来，我会很高兴。

感谢任何建议。

Answer 1

应该为 View 设置自动布局。如果是，请确保在设置原始位置后更新约束。

func handlePan(panGesture: UIPanGestureRecognizer){

    switch panGesture.state{

    case .Began:
        // start flying

    case .Changed:
        // follow the pan
        let dCenter = panGesture.translationInView(view)
        chicken.center = CGPointMake(chicken.center.x + dCenter.x, chicken.center.y + dCenter.y)
        panGesture.setTranslation(CGPointZero, inView: view)

    case .Ended:
        // fly back
        if originalChickenPosition != nil{
          chicken.center = originalChickenPosition!
        }
        **self.chicken.setNeedsUpdateConstraints()**
        default: break

    }   
}