Question

我曾尝试结合众多教程，尝试使手势识别器在mapView上收到手势后在tableView上启动动画（一旦地图像旧的超级应用程序一样移动，缩小表）。动画功能，但是一旦动画完成，我就会收到＆＃34;意外地发现nil在打开一个可选的＆＃34; - 但它似乎不应该是零，显然它是，我只是不明白如何。错误是下降的3/4，我试图减少尽可能多的代码，因此缺少部分。我的猜测是我创建了2个手势识别器，导致了这个问题，但我不确定如何将它们组合起来。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，因为您从未实际分配过它。

在viewDidLoad()函数中，您实际上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，而是将其指定为：

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

Answer 2

这可以在不存储对手势识别器的引用的情况下仍然有效。您可以将传递到handlePan的手势识别器中的值传递到startAnimation和endAnimation。这样可以减少在类上具有多余属性的需要

为什么我的gestureRecognizer返回nil？

2 个答案: