Question

[类型'MapViewController'没有成员'mapTypeChanged'] [2] 在线：

action: #selector(MapViewController.mapTypeChanged(_:)),

代码底部有一个方法mapTypeChanged，所以我不确定为什么错误说没有成员mapTypeChanged？我猜想mapTypeChanged需要声明为变量（全局？）

import UIKit
import MapKit


class MapViewController: UIViewController {

    var mapView: MKMapView!

    override func loadView() {

        mapView = MKMapView()
        view = mapView

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

        segmentedControl.addTarget(self,
                                   action: #selector(MapViewController.mapTypeChanged(_:)),
                                   for: .valueChanged)
segmentedControl.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(segmentedControl)

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

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

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


    override func viewDidLoad() {
        super.viewDidLoad()

        print("MapViewController Loaded its view.")

    }

}

Answer 1

#selector(MapViewController.mapTypeChanged(_:))

表示“调用mapTypeChanged方法”。

所以你需要实现mapTypeChanged。

func mapTypeChanged(_ sender: UISegmentedControl) {
    print(sender.selectedSegmentIndex)
}

Answer 2

对于Xcode 9.3.1，函数mapTypeChanged必须在 override func loadView()之外，并且前面是@objc：

@objc func mapTypeChanged(_ segControl: UISegmentedControl) {
        switch segControl.selectedSegmentIndex {
        case 0:
            ...
        }
    }

@objc属性使您的Swift API在Objective-C和Objective-C运行时可用。

类型'MapViewController'没有成员'mapTypeChanged'Swift Big Nerd Ranch Guide

2 个答案: