当从另一个 ObservedObject 链接时，View 不会对 Published 属性的更改做出反应

Question

下面是 SwiftUI 视图，它拥有一个 ViewModel，逻辑是如果 viewModel.authenticationService.user 包含一个用户对象，那么它将显示 HomeView，否则将要求登录。所以最初 viewModel.authenticationService.user 是 nil 并且用户登录成功用户对象不再是 nil.

查看

struct WelcomeView: View {
    
    @ObservedObject private var viewModel: WelcomeView.Model
    @State private var signInActive: Bool = false
    
    init(viewModel: WelcomeView.Model) {
        self.viewModel = viewModel
    }
    
    var body: some View {
        if viewModel.authenticationService.user != nil {
            HomeView()
        } else { 
            LoginView()
        }
    }

ViewModel

extension WelcomeView {
    
    final class Model: ObservableObject {
        
        @ObservedObject var authenticationService: AuthenticationService
        
        init(authenticationService: AuthenticationService) {
            self.authenticationService = authenticationService
        }
    }
}

AuthenticationService

final class AuthenticationService: ObservableObject {
    
    @Published var user: User?
    private var authenticationStateHandle: AuthStateDidChangeListenerHandle?
    
    init() {
        addListeners()
    }
    
    private func addListeners() {
        if let handle = authenticationStateHandle {
            Auth.auth().removeStateDidChangeListener(handle)
        }
        
        authenticationStateHandle = Auth.auth()
            .addStateDidChangeListener { _, user in
                self.user = user
            }
    }
    
    static func signIn(email: String, password: String, completion: @escaping AuthDataResultCallback) {
        if Auth.auth().currentUser != nil {
            Self.signOut()
        }
        Auth.auth().signIn(withEmail: email, password: password, completion: completion)
    }
}

但是，当用某个值更新用户对象时，它不会更新视图。我不确定，因为我是反应式编程方式的新手。有一个 View -> ViewModel -> Service 链，发布的用户属性在 Service class 中，一旦用户登录就会成功更新。

我是否需要在 ViewModel 中添加一个侦听器来响应已发布的服务属性？或者有什么直接的方法可以使这种情况起作用并获得 UI 更新？

Answer 1

如果存在从 View -> ViewModel -> Services 的链的情况：

@ObservedObject 不适用于类。仅适用于 SwiftUI 视图（结构）。因此，如果您想从服务中观察视图模型的变化，您需要手动 listen/subscribe 它。

self.element.$value.sink(
                receiveValue: { [weak self] _ in
                    self?.objectWillChange.send()
                }
            )

您也可以使用.assign。查找更多详细信息 here

当从另一个 ObservedObject 链接时，View 不会对 Published 属性的更改做出反应

View not reacting to changes of Published property when its chained from another ObservedObject

swift

swiftui

combine

当从另一个 ObservedObject 链接时，View 不会对 Published 属性 的更改做出反应

View not reacting to changes of Published property when its chained from another ObservedObject

swift

swiftui

combine

当从另一个 ObservedObject 链接时，View 不会对 Published 属性的更改做出反应