swift - 如何让Published属性只在收到数据时调用map

Question

我是 Combine 的新手，我正在尝试创建一个登录流程，其中:

• 当我点击登录按钮时，应用会触发 GoogleSignIn sign 函数
• 然后，当 GoogleDelegate 收到 session 数据时，它需要启动对我的服务器端登录方法的请求。

为此，我有一个控制登录过程的 GoogleSignInController:

class GoogleSignInController: GIDSignInDelegate {
    @Published var onSessionAcquired: GoogleSignInSessionData = ("", "")

    func signIn() {
        if (GIDSignIn.sharedInstance()?.presentingViewController == nil) {
            GIDSignIn.sharedInstance()?.presentingViewController = UIApplication.shared.windows.last?.rootViewController
        }
        GIDSignIn.sharedInstance()?.signIn()
    }

    func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error!) {
        if let error = error {
            if (error as NSError).code == GIDSignInErrorCode.hasNoAuthInKeychain.rawValue {
                print("The user has not signed in")
            } else {
                print("\(error.localizedDescription)")
            }
            return
        }
        
        onSessionAcquired = GoogleSignInSessionData(idToken: user.authentication.idToken ?? "", serverAuthCode: user.serverAuthCode ?? "")
        
        print("Successful sign-in!")
        signedIn = true
    }
}

然后在 ViewModel 中，我使用一些状态来控制过程:

    static func whenStartedLogin() -> Feedback<State, Event> {
        Feedback { (state: State) -> AnyPublisher<Event, Never> in
            guard case .loadingGoogleSignIn = state else { return Empty().eraseToAnyPublisher() }

            GoogleSignInController.shared.signIn()
            
            return GoogleSignInController.shared.$onSessionAcquired
                .receive(on: DispatchQueue.main)
                .map { Event.onGoogleSessionAcquired($0) }
                .eraseToAnyPublisher()
        }
    }

    static func whenReceivedGoogleSession() -> Feedback<State, Event> {
        Feedback { (state: State) -> AnyPublisher<Event, Never> in
            guard case let .loadingServerSession(googleSession) = state else { return Empty().eraseToAnyPublisher() }

            return self.signIn(idToken: googleSession.idToken, serverAuthCode: googleSession.serverAuthCode)
              .map { (userInfo, error) in
                  if let error = error {
                      return Event.onFailedToAcquireSession(error)
                  } else if let userInfo = userInfo {
                      return Event.onUserInfoAcquired(userInfo)
                  } else {
                      return Event.onFailedToAcquireSession(AppError.unknown)
                  }
              }
              .eraseToAnyPublisher()
        }
    }

问题是:当我点击登录按钮时，whenStatedLogin 函数被触发，它将我的事件映射到 Event.onGoogleSessionAcquired。这应该仅在 onSessionAcquired 更改时映射(在调用 sign 委托(delegate)之后)。我该怎么做？

Answer 1

刚想出这个问题的解决方案。在我的案例中要使用的正确数据类型是 PassthroughSubject。

let sessionSubject = PassthroughSubject<GoogleSignInSessionData, Never>()

...

func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error!) {
    if let error = error {
        if (error as NSError).code == GIDSignInErrorCode.hasNoAuthInKeychain.rawValue {
            print("The user has not signed in")
        } else {
            print("\(error.localizedDescription)")
        }
        return
    }
    
    sessionSubject.send(GoogleSignInSessionData(idToken: user.authentication.idToken ?? "", serverAuthCode: user.serverAuthCode ?? ""))
    
    print("Successful sign-in!")
    signedIn = true
}

采用这种方式将使 map 仅在主题接收到事件时调用。