为什么我的 gestureRecognizer 返回零？

Question

我尝试结合许多教程来尝试让手势识别器在 tableView 上启动动画一旦在 mapView 上接收到手势（一旦地图移动就收缩 table旧的优步应用程序）。动画功能，但是一旦动画完成我收到 "unexpectedly found nil when unwrapping an optional" - 但它似乎不应该为零，显然它是，我只是不明白如何。错误是向下的 3/4，我试图减少尽可能多的代码，所以部分丢失了。我的猜测是我创建了 2 个导致问题的手势识别器，但我不确定如何组合它们。这是代码：

    class RestaurantsVC: UIViewController, MKMapViewDelegate, CLLocationManagerDelegate, UIGestureRecognizerDelegate {

    var animator: UIViewPropertyAnimator?
    var currentState: AnimationState!
    var thumbnailFrame: CGRect!
    var panGestureRecognizer: UIPanGestureRecognizer!

    override func viewDidLoad() {
        super.viewDidLoad()

        let panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(RestaurantsVC.handlePan(gestureRecognizer:)))
        panGestureRecognizer.delegate = self
        self.mapView.addGestureRecognizer(panGestureRecognizer)
}

    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        return true
    }


    @objc func handlePan (gestureRecognizer: UIPanGestureRecognizer) {
        let translation = gestureRecognizer.translation(in: self.view.superview)

        switch gestureRecognizer.state {
        case .began:
            startPanning()
            animator?.startAnimation()
        case .ended:
            let velocity = gestureRecognizer.velocity(in: self.view.superview)
            endAnimation(translation: translation, velocity: velocity)
        default:
            print("Something went wrong handlePan")
        }
    }


    func startPanning() {
        var finalFrame:CGRect = CGRect()
        switch currentState {
           // code
        }
        animator = UIViewPropertyAnimator(duration: 1, dampingRatio: 0.8, animations: {
        })
    }


    func endAnimation (translation:CGPoint, velocity:CGPoint) {

            if let animator = self.animator {
                self.panGestureRecognizer.isEnabled = false //(this line is where i get the error)//

                switch self.currentState {
                case .thumbnail:
                        animator.isReversed = false
                        animator.addCompletion({ _ in
                            self.currentState = .minimized
                            self.panGestureRecognizer.isEnabled = true
                        })
                case .minimized:
                        animator.isReversed = true
                        animator.addCompletion({ _ in
                            self.currentState = .thumbnail
                            self.panGestureRecognizer.isEnabled = true
                        })
                default:
                    print("unknown state")
                }
            }
    }
}

Answer 1

它是 nil 因为你从来没有真正分配它。

在您的 viewDidLoad() 函数中，您实际上是在 重新定义 一个隐藏实例变量的局部变量：

let panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(RestaurantsVC.handlePan(gestureRecognizer:)))
^ The 'let' keyword is redefining this variable at the local scope

您应该删除 let 声明，并将其指定为：

self.panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(RestaurantsVC.handlePan(gestureRecognizer:)))

Answer 2

这仍然可以在不存储对手势识别器的引用的情况下工作。您可以将传递到 handlePan 的手势识别器的值传递到 startAnimation 和 endAnimation。这将减少在 class

上拥有多余属性的需要

为什么我的 gestureRecognizer 返回零？

why is my gestureRecognizer returning nil?

swift

uipangesturerecognizer