如何使用 ObservableObject 更新 UIViewRepresentable

Question

我正在尝试学习与 SwiftUI 结合，我正在努力如何使用 ObservableObject（以前的 BindableObject）更新我的视图（来自 UIKit）。问题是，很明显，一旦@Published 对象发送它已更改的通知，方法updateUIView 将不会触发。

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locationCoordinates 数组绑定到视图，这样每次刷新时实际上都会添加一个新点？

Answer 1

我将为使用 combine 表示的任何 UI/NS 视图提供通用解决方案。我的方法有性能优势。

1. 创建了一个 Observable 对象并用 @Published 包装器
2. 在视图中通过updateView方法注入Observed对象 可使用您将在第 3 步中创建的方法表示
3. 使用视图模型作为参数对所需视图进行子类化。 创建一个 addViewModel 方法并使用 合并运营商/订阅者并将其添加到可取消。

注意 - 非常适用于环境对象。

    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)
      }
    }

Answer 2

这个解决方案对我有用，但使用 EnvironmentObject https://gist.github.com/svanimpe/152e6539cd371a9ae0cfee42b374d7c4

Answer 3

为确保您的ObservedObject 不会被多次创建（您只需要一份），您可以将其放在您的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)
    }
}