Swift 处理 Actions 和 Selectors 问题 -

Question

什么给了？我不断收到的错误是在 action 参数的第一行。我试过“mapTypeChanged:”......#selector(mapTypeChanged)......等等......我不断收到黄色或红色错误。这是怎么回事？

   class viewControllerForMap: UIViewController {

    var mapView : MKMapView!

    override func loadView() {
        mapView = MKMapView()
        self.view = mapView

        let segmentedControl = UISegmentedControl(items: ["Standard", "Hybrid", "Satellite"])
        segmentedControl.backgroundColor = UIColor.white.withAlphaComponent(0.5)
        segmentedControl.selectedSegmentIndex = 0
        segmentedControl.translatesAutoresizingMaskIntoConstraints = false
        self.view.addSubview(segmentedControl)

        segmentedControl.addTarget(self, action: #selector(mapTypeChanged(_:)), for: .valueChanged)

        func mapTypeChanged(_ sender: UISegmentedControl) {
            switch sender.selectedSegmentIndex {
            case 0:
                mapView.mapType = .standard
            case 1:
                mapView.mapType = .hybrid
            case 2:
                mapView.mapType = .satellite
            case _:
                break
            }
        }

        let topConstraint = segmentedControl.topAnchor.constraint(equalTo: self.topLayoutGuide.bottomAnchor, constant: 8)
        let leadingConstraint = segmentedControl.leadingAnchor.constraint(equalTo: self.view.layoutMarginsGuide.leadingAnchor)
        let trailingConstraint = segmentedControl.trailingAnchor.constraint(equalTo: self.view.layoutMarginsGuide.trailingAnchor)

        topConstraint.isActive = true
        leadingConstraint.isActive = true
        trailingConstraint.isActive = true

    }

}

Answer 1

根据更新后的代码，问题似乎出在您的

func mapTypeChanged(_ sender: UISegmentedControl) {
            switch sender.selectedSegmentIndex {
            case 0:
                mapView.mapType = .standard
            case 1:
                mapView.mapType = .hybrid
            case 2:
                mapView.mapType = .satellite
            case _:
                break
            }
        }

函数当前在您的其他方法中。

它应该是这样的:

    class viewControllerForMap: UIViewController {

        var mapView : MKMapView!

        override func loadView() {
            mapView = MKMapView()
            self.view = mapView

            let segmentedControl = UISegmentedControl(items: ["Standard", "Hybrid", "Satellite"])
            segmentedControl.backgroundColor = UIColor.white.withAlphaComponent(0.5)
            segmentedControl.selectedSegmentIndex = 0
            segmentedControl.translatesAutoresizingMaskIntoConstraints = false
            self.view.addSubview(segmentedControl)

            segmentedControl.addTarget(self, action: #selector(mapTypeChanged(_:)), for: .valueChanged)

            let topConstraint = segmentedControl.topAnchor.constraint(equalTo: self.topLayoutGuide.bottomAnchor, constant: 8)
            let leadingConstraint = segmentedControl.leadingAnchor.constraint(equalTo: self.view.layoutMarginsGuide.leadingAnchor)
            let trailingConstraint = segmentedControl.trailingAnchor.constraint(equalTo: self.view.layoutMarginsGuide.trailingAnchor)

            topConstraint.isActive = true
            leadingConstraint.isActive = true
            trailingConstraint.isActive = true

        }

func mapTypeChanged(_ sender: UISegmentedControl) {
                switch sender.selectedSegmentIndex {
                case 0:
                    mapView.mapType = .standard
                case 1:
                    mapView.mapType = .hybrid
                case 2:
                    mapView.mapType = .satellite
                case _:
                    break
                }
            }

    }

希望对您有所帮助。