在 SwiftUI 视图中实现委托

Question

我正在尝试实现需要委托方法的功能（如NSUserActivity）。因此，我需要一个符合NSUserActivityDelegate（或类似的其他代表）的UIViewController，处理并保存所有必需的信息。我的问题是我的界面使用了 SwiftUI，因此我没有使用UIViewControllers。那么我怎样才能实现这个功能并且仍然使用 SwiftUI 作为 UI。我尝试过：view1 只是一个普通的 SwiftUI View，可以呈现（通过 NavigationLink）view2，这是想要实现此功能的视图。所以我尝试不链接 view1 和 view2，而是将 view1 链接到 UIViewControllerRepresentable，然后处理此功能的实现并将 UIHostingController(rootView: view2) 添加为子视图控制器。

struct view1: View {    
    var body: some View {
        NavigationLink(destination: VCRepresentable()) {
            Text("Some Label")
        }
    }
}

struct view2: View {    
    var body: some View {
        Text("Hello World!")
    }
}

struct VCRepresentable: UIViewControllerRepresentable {
    func makeUIViewController(context: Context) -> UIViewController {
        return implementationVC()
    }

    func updateUIViewController(_ uiViewController: UIViewController, context: Context) { }
}

class implementationVC: UIViewController, SomeDelegate for functionality {
    // does implementation stuff in delegate methods
    ...

    override func viewDidLoad() {
        super.viewDidLoad()

        attachChild(UIHostingController(rootView: view2()))
    }

    private func attachChild(_ viewController: UIViewController) {
        addChild(viewController)

        if let subview = viewController.view {
            subview.translatesAutoresizingMaskIntoConstraints = false
            view.addSubview(subview)

            subview.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
            subview.heightAnchor.constraint(equalTo: view.heightAnchor).isActive = true
            subview.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
            subview.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
        }

        viewController.didMove(toParent: self)
    }
}

我在 VC 和 view2 之间传输数据时遇到问题。所以我想知道是否有更好的方法在 SwiftUI 视图中实现这样的功能。

Answer 1

您需要创建一个符合UIViewControllerRepresentable 的视图，并拥有一个处理所有委托功能的Coordinator。

例如，使用您的示例视图控制器和委托：

struct SomeDelegateObserver: UIViewControllerRepresentable {
    let vc = SomeViewController()
    var foo: (Data) -> Void
    func makeUIViewController(context: Context) -> SomeViewController {
        return vc
    }

    func updateUIViewController(_ uiViewController: SomeViewController, context: Context) { }
    func makeCoordinator() -> Coordinator {
        Coordinator(vc: vc, foo: foo)
    }

    class Coordinator: NSObject, SomeDelegate {
        var foo: (Data) -> Void
        init(vc: SomeViewController, foo: @escaping (Data) -> Void) {
            self.foo = foo
            super.init()
            vc.delegate = self
        }
        func someDelegateFunction(data: Data) {
            foo(data)
        }
    }
}

用法：

struct ContentView: View {
    var dataModel: DataModel

    var body: some View {
        NavigationLink(destination: CustomView(numberFromPreviousView: 10)) {
            Text("Go to VCRepresentable")
        }
    }
}

struct CustomView: View {
    @State var instanceData1: String = ""
    @State var instanceData2: Data?
    var numberFromPreviousView: Int // example of data passed from the previous view to this view, the one that can react to the delegate's functions
    var body: some View {
        ZStack {
            SomeDelegateObserver { data in
                print("Some delegate function was executed.")
                self.instanceData1 = "Executed!"
                self.instanceData2 = data
            }
            VStack {
                Text("This is the UI")
                Text("That, in UIKit, you would have in the UIViewController")
                Text("That conforms to whatever delegate")
                Text("SomeDelegateObserver is observing.")
                Spacer()
                Text(instanceData1)
            }
        }
    }
}

注意：我将 VCRepresentable 重命名为 SomeDelegateObserver 以更能说明它的作用：它的唯一目的是等待委托函数执行然后运行闭包（即 @987654328 @ 在这个例子中）你提供它。您可以使用此模式创建任意数量的函数来“观察”您关心的任何委托函数，然后执行可以更新 UI、数据模型等的代码。在我的示例中，当 SomeDelegate 触发 @ 987654330@，视图将显示“已执行”并更新数据实例变量。