如何仅在接收数据时制作已发布的属性调用映射

Posted 2023-02-24

【中文标题】如何仅在接收数据时制作已发布的属性调用映射

【英文标题】：How to make a Published property call map only when it receives data

【发布时间】：2021-06-02 11:12:49

【问题描述】：

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，当在 GoogleDelegate 上接收到会话数据时，它需要向我的服务器端登录方法发起请求。

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流程：

    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，它将我的事件映射为Event.onGoogleSessionAcquired。仅当 onSessionAcquired 更改时（在调用 sign 委托之后）才应该映射它。我该怎么做？

【参考方案1】：

刚刚想出了解决这个问题的方法。在我的例子中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

以这种方式使地图仅在主题收到事件时才被调用。