如何用UIViewRepresentable更新ObservableObject

Question

我正在努力学习如何与SwiftUI结合，并且我正在挣扎如何用ObservableObject (以前的BindableObject)更新我的视图(从UIKit)。问题是，显然，一旦updateUIView对象发送已更改的通知，@Published方法就不会触发。

class DataSource: ObservableObject {
    @Published var locationCoordinates = [CLLocationCoordinate2D]()
    var value: Int = 0

    init() {
        Timer.scheduledTimer(withTimeInterval: 3, repeats: true) { timer in
            self.value += 1
            self.locationCoordinates.append(CLLocationCoordinate2D(latitude: 52, longitude: 16+0.1*Double(self.value)))
        }
    }
}

struct MyView: UIViewRepresentable {
    @ObservedObject var dataSource = DataSource()

    func makeUIView(context: Context) -> MKMapView {
        MKMapView(frame: .zero)
    }

    func updateUIView(_ view: MKMapView, context: Context) {
        let newestCoordinate = dataSource.locationCoordinates.last ?? CLLocationCoordinate2D(latitude: 52, longitude: 16)
        let annotation = MKPointAnnotation()
        annotation.coordinate = newestCoordinate
        annotation.title = "Test #\(dataSource.value)"
        view.addAnnotation(annotation)
    }
}

如何将该locationCoordinates数组绑定到视图，即每次刷新时都会添加一个新的点？

Answer 1

为了确保您的ObservedObject不会多次被创建(您只需要它的一个副本)，您可以将它放在UIViewRepresentable之外

import SwiftUI
import MapKit

struct ContentView: View {
    @ObservedObject var dataSource = DataSource()

    var body: some View {
        MyView(locationCoordinates: dataSource.locationCoordinates, value: dataSource.value)
    }
}
class DataSource: ObservableObject {
    @Published var locationCoordinates = [CLLocationCoordinate2D]()
    var value: Int = 0

    init() {
        Timer.scheduledTimer(withTimeInterval: 3, repeats: true) { timer in
            self.value += 1
            self.locationCoordinates.append(CLLocationCoordinate2D(latitude: 52, longitude: 16+0.1*Double(self.value)))
        }
    }
}

struct MyView: UIViewRepresentable {
    var locationCoordinates: [CLLocationCoordinate2D]
    var value: Int

    func makeUIView(context: Context) -> MKMapView {
        MKMapView(frame: .zero)
    }

    func updateUIView(_ view: MKMapView, context: Context) {
        print("I am being called!")
        let newestCoordinate = locationCoordinates.last ?? CLLocationCoordinate2D(latitude: 52, longitude: 16)
        let annotation = MKPointAnnotation()
        annotation.coordinate = newestCoordinate
        annotation.title = "Test #\(value)"
        view.addAnnotation(annotation)
    }
}

Answer 2

这个解决方案适用于我，但适用于EnvironmentObject https://gist.github.com/svanimpe/152e6539cd371a9ae0cfee42b374d7c4。

Answer 3

我将提供一个通用的解决方案，任何UI/NS视图表示使用组合。我的方法有性能上的好处。

1. 创建一个可观察的对象，并使用@已发布的包装器包装所需的属性。
2. 使用步骤3中的方法通过可表示的视图中的updateView方法注入所观察到的对象
3. 用视图模型作为参数对所需的视图进行子类。创建一个addViewModel方法，并使用组合运算符/订阅服务器并将它们添加到可取消的。

注意--对环境对象非常有用。

    struct swiftUIView : View {
      @EnvironmentObject var env : yourViewModel
      ...
      ...
          UIViewRep(wm : env)
     }

    struct UIViewRep : UIViewRepresentable {

     var wm : yourViewModel
     
     func makeUIView {
      let yv = yourView()
      yv.addViewModel(wm)
      return yv
      }}

    class yourView : UIView {
     var viewModel : yourViewModel?
     var cancellable = Set<AnyCancellable>()
     ...
     ...
     func addViewModel( _ wm : yourViewModel) {
     self.viewModel = wm

      self.viewModel?.desiredProperty
          .sink(receiveValue: { [unowned self] w in
        print("Make changes with ", w)
       }).store(in: &cancellable)
      }
    }