将 @Published 属性从视图控制器传递给 SwiftUI

Question

假设您有一个我想与 SwiftUI 一起使用的旧版视图控制器。视图控制器有一个包含当前状态的 @Published 属性：

class LegacyViewController: UIViewController {
    enum State {
        case opened
        case closed
        case halfOpened
    }
    
    @Published var state: State
    
    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
        self.state = .closed
        super.init(nibName: nil, bundle: nil)
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // state is changed after some time
    }
}

理想情况下，我想像这样在 SwiftUI 中使用它：

struct ContentView: View {
    @State var state: LegacyViewController.State
    
    var body: some View {
        VCWrapper(state: $state).overlay (
            Text("\(state)")
        )
    }
}

这意味着我需要实现UIViewControllerRepresentable 协议：

struct VCWrapper: UIViewControllerRepresentable {
    @Binding var state: LegacyViewController.State
    
    func makeUIViewController(context: Context) -> LegacyViewController {
        let vc = LegacyViewController(nibName: nil, bundle: nil)
        /// where to perform the actual binding?
        return vc
    }
    
    func updateUIViewController(_ uiViewController: LegacyViewController, context: Context) {
        
    }
}

但是，我无法确定从LegacyViewController 的state 属性到VCWrapper 公开的state 属性的实际绑定位置。如果LegacyViewController 暴露了一个委托，我可以通过Coordinator 对象实现绑定，但考虑到我不使用委托对象，我不太确定如何执行此操作？

Answer 1

这是可能的解决方案 - 使用 Combine。使用 Xcode 12 / iOS 14 测试。

import Combine

struct VCWrapper: UIViewControllerRepresentable {
    @Binding var state: LegacyViewController.State
    
    func makeUIViewController(context: Context) -> LegacyViewController {
        let vc = LegacyViewController(nibName: nil, bundle: nil)

        // subscribe to controller state publisher and update bound
        // external state
        context.coordinator.cancelable = vc.$state
            .sink {
               DispatchQueue.main.async {
                  _state.wrappedValue = $0
               }
            }

        return vc
    }
    
    func updateUIViewController(_ uiViewController: LegacyViewController, context: Context) {
    }
    
    func makeCoordinator() -> Coordinator {
        Coordinator()
    }
    
    class Coordinator {
        var cancelable: AnyCancellable?
    }
}