SwiftUI视图外部变量无法更新？导航跳转失效问题求助

问题根源 #

• 协调器错误使用@State：@State仅适用于SwiftUI的View结构体，在ObservableObject子类（如ChooseIDViewCoordinator）中需用@Published触发视图更新。
• 状态更新方式不合理：直接调用视图结构体的updateLink方法不可靠——SwiftUI视图是值类型，随时可能被重建，持有实例调用方法操作的往往不是当前渲染的视图。
• ViewModel回调未正确关联：ViewModel的授权结果应通知协调器，由协调器更新导航状态，而非直接操作视图变量。

修复步骤 #

1. 修正协调器的状态属性与回调逻辑 #

将协调器中的@State替换为@Published，并实现ViewModel的delegate方法处理授权成功后的导航触发：

@MainActor
class ChooseIDViewCoordinator: ObservableObject, ChooseIDViewModelDelegate {
    @Published var parent: LoggedOutCoordinator?
    @Published var shouldNavigateToFaceID: Bool = false // 替换@State为@Published

    var viewModel = ChooseIDViewModel()
    var mainView: ChooseIDView!

    init(parent: LoggedOutCoordinator?) {
        self.parent = parent
    }

    func view() -> some View {
        mainView = ChooseIDView(viewModel: viewModel, shouldGoForSelectAvatarScreen: $shouldNavigateToFaceID)
        self.viewModel.delegate = self
        return mainView
    }

    // 实现ViewModel的delegate方法，授权成功时更新导航状态
    func authorizationDidSucceed() {
        self.shouldNavigateToFaceID = true
    }
}

2. 清理视图中的冗余代码 #

移除视图中无用的updateLink方法，依赖Binding接收协调器的状态变化：

public struct ChooseIDView: View {
    var viewModel: ChooseIDViewModel
    @Binding var shouldGoForSelectAvatarScreen: Bool
    
    @State private var textFieldID = ""
    
    public var body: some View {
        NavigationStack {
            VStack(alignment: .leading, spacing: 10) {
                HStack(alignment: .center, spacing: 5.0) {}
                Spacer()
                ZStack(alignment: .bottom) {
                    VStack(spacing: 5) {
                        Text("Choose Wzrd ID")
                            .font(.title)
                            .multilineTextAlignment(.center)
                            .frame(maxWidth: .infinity, minHeight: 30)
                            .font(.body)
                            .bold()
                        PrimaryTextField(placeholder: "Enter your name", secretText: false)
                        PrimaryTextField(placeholder: "Enter your password", secretText: true)
                        PrimaryButton(action: {
                            self.viewModel.requestAuthorization()
                        }, title: "Next")
                    }.padding()
                }
            }
            FaceIDView()
                .navigatePush(when: $shouldGoForSelectAvatarScreen, matches: true)

            Button("toggle") {
                self.shouldGoForSelectAvatarScreen = true
            }
        }
    }
}

3. 完善ViewModel的Delegate协议 #

确保ViewModel通过协议传递授权结果：

protocol ChooseIDViewModelDelegate: AnyObject {
    func authorizationDidSucceed()
}

class ChooseIDViewModel {
    weak var delegate: ChooseIDViewModelDelegate?

    func requestAuthorization() {
        // 模拟授权逻辑，成功后通知delegate（确保在主线程执行）
        DispatchQueue.main.async {
            self.delegate?.authorizationDidSucceed()
        }
    }
}

4. 验证自定义导航修饰符 #

确保navigatePush正确监听Binding变化，示例实现如下：

extension View {
    func navigatePush<Destination: View>(when binding: Binding<Bool>, matches value: Bool, @ViewBuilder destination: () -> Destination) -> some View {
        self.background(
            NavigationLink(
                isActive: binding,
                destination: destination,
                label: { EmptyView() }
            )
        )
    }
}

核心逻辑说明 #

协调器作为视图与ViewModel的中间层，负责接收业务回调并更新导航状态；通过@Published+Binding的数据流，让状态变化自动驱动视图更新，完全符合SwiftUI的状态管理原则。

内容的提问来源于stack exchange，提问作者Matheus Weber