如何使用设置 MKMapView 仅放大一次？然后每次之后它应该只添加注释而不缩放

Question

我希望地图在打开时放大到伦敦的 3 个位置。然后 7 秒后，我希望柏林位置显示在地图上，但我不希望地图放大它们。我希望用户始终可以滚动地图，而不会在任何地方“跳转”。我猜这可能与我对 SwiftUI 工作原理的理解有关。但我不明白如何。这是一些代码，显示了我想要实现的目标。或者您可以在此处获取工作示例 -> https://github.com/cameronhenige/TestSwiftUIMapZoom。在当前状态下，它会放大到伦敦位置，然后 7 秒后它会同时放大到伦敦和柏林位置。


import SwiftUI
import MapKit

struct ContentView: View {
    
    @ObservedObject var testViewModel = TestViewModel()
    @State var map = MKMapView()

    var SearchingButtonText: some View {
            return Text("Test" )
    }
    
    var body: some View {
            VStack {
            
                TestMapView(map: self.$map, locations: $testViewModel.locations)
                
            }.onAppear() {
                self.testViewModel.fetchData()
              }
    }
}



import Foundation
import CoreLocation
import MapKit

class TestViewModel: NSObject, ObservableObject {
    
    @Published var locations: [MKPointAnnotation] = []
    
    func fetchData() {
        
        let london = MKPointAnnotation()
        london.title = "London"
        london.coordinate = CLLocationCoordinate2D(latitude: 51.507222, longitude: -0.1275)
        
        let londonTwo = MKPointAnnotation()
        londonTwo.title = "London Two"
        londonTwo.coordinate = CLLocationCoordinate2D(latitude: 51.507224, longitude: -0.1277)
        
        
        let londonThree = MKPointAnnotation()
        londonThree.title = "London Three"
        londonThree.coordinate = CLLocationCoordinate2D(latitude: 51.507226, longitude: -0.1279)
        

        let berlin = MKPointAnnotation()
        berlin.title = "Berlin"
        berlin.coordinate = CLLocationCoordinate2D(latitude: 52.5200, longitude: 13.4050)
        
        let berlinTwo = MKPointAnnotation()
        berlinTwo.title = "Berlin Two"
        berlinTwo.coordinate = CLLocationCoordinate2D(latitude: 52.5202, longitude: 13.4052)
        
        
        let berlinThree = MKPointAnnotation()
        berlinThree.title = "Berlin Three"
        berlinThree.coordinate = CLLocationCoordinate2D(latitude: 52.5204, longitude: 13.4056)
        
    
        
        locations.append(london)
        locations.append(londonTwo)
        locations.append(londonThree)
        //These should initially zoom in.
        
        let seconds = 7.0
        DispatchQueue.main.asyncAfter(deadline: .now() + seconds) {
            self.locations.append(berlin)
            self.locations.append(berlinTwo)
            self.locations.append(berlinThree)
            //These should just appear on the map but not pan the map to show them.
        }

    }
    
    
}


import SwiftUI
import MapKit

struct TestMapView: UIViewRepresentable {
    
    @Binding var map : MKMapView
    @Binding var locations: [MKPointAnnotation]
    @State var hasZoomed = false
    
    func makeUIView(context: Context) -> MKMapView {
        return map
    }
    
    func updateUIView(_ view: MKMapView, context: Context) {
        self.map.addAnnotations(locations)
        
        //I only want to call this once.
        if(!hasZoomed && !self.locations.isEmpty) {
            self.map.showAnnotations(locations, animated: false)
            hasZoomed = true //here i get a warning "Modifying state during view update, this will cause undefined behavior."
        }
    }
}

Answer 1

代码中存在一些不规范之处。

当您创建一个 UIViewRepresentable 视图时，该结构负责 UIKit 视图分配/更新。

地图创建为 @State 并传入，我认为这不是正确的方法。

您可以尝试这样的操作：

struct TestMapView: UIViewRepresentable {

    final class Coordinator {
        var hasZoomed = false
    }
    
    @Binding var locations: [MKPointAnnotation]

    func makeCoordinator() -> Coordinator {
        Coordinator()
    }
    
    func makeUIView(context: Context) -> MKMapView {
        return MKMapView(frame: .zero)
    }
    
    func updateUIView(_ view: MKMapView, context: Context) {
        view.removeAnnotations(view.annotations)
        view.addAnnotations(locations)
        if(!context.coordinator.hasZoomed && !self.locations.isEmpty) {
            view.showAnnotations(locations, animated: false)
            context.coordinator.hasZoomed = true
        }
    }
}

在视图模型中，您可能想要这样做...

locations.append(contentsOf: [london, londonTwo, londonThree])

...而不是附加一个位置。

每次附加一个，都会触发一个新事件 (@Published)。在您的场景中，您似乎想要触发两个事件：第一个事件针对伦敦地点，第二个事件针对柏林地点。

更新：我在 Github

上将我的建议作为 PR 添加到您的回购协议中

如何使用设置 MKMapView 仅放大一次？然后每次之后它应该只添加注释而不缩放

How can I use set up an MKMapView to only zoom in once? Then every time after it should just add annotations without zooming

swift

swiftui

mapkit

mkmapview