为什么我的快速代码执行无序？ Firebase 身份验证答案

【问题标题】：Why is my swift code executing out of order? Firebase authentication为什么我的快速代码执行无序？ Firebase 身份验证
【发布时间】：2021-02-19 16:13:38
【问题描述】：

我正在调用Authenticator.loginUser()，期望该方法将登录用户然后调用getCurrentUser()。根据打印输出，getCurrentUser() 首先执行。有没有办法强制它按顺序执行？

class Authenticator: ObservableObject {
        
        @Published var currentUser: UserProfile = UserProfile()
        @Published var user: String = ""
        @Published var documentId: String = ""
            
        func loginUser (email: String, password: String, viewModel: UsersViewModel) {
            FirebaseAuth.Auth.auth().signIn(withEmail: email, password: password, completion: { result, error in
                
                guard error == nil else {
                    print ("error: \(error!)")
                    return
                }
                print ("user signed in")
            })
            self.user = self.getCurrentUser(viewModel: viewModel)
        }
        
        func getCurrentUser(viewModel: UsersViewModel) -> String {
            guard let userID = Auth.auth().currentUser?.uid else {
                return ""
            }
            
            viewModel.users.forEach { i in
                if (i.userId == userID) {
                    currentUser = i
                }
            }
            
            documentId = currentUser.documentId!
            print("auth.documentId \(documentId)")
            return userID
        }
        
    }

【问题讨论】：

programmingios.net/what-asynchronous-means

标签： swift firebase firebase-authentication swiftui

【解决方案1】：

FirebaseAuth.Auth.auth().signIn 是异步 - 它在 background 中运行，而 not 在 main 线程上运行。这意味着signIn 将在将来的某个时间被调用。

一种解决方案是将调用 getCurrentUser 放在完成块中：

func loginUser(email: String, password: String, viewModel: UsersViewModel) {
    FirebaseAuth.Auth.auth().signIn(withEmail: email, password: password, completion: { result, error in
        guard error == nil else {
            print("error: \(error!)")
            return
        }
        print("user signed in")
        self.user = self.getCurrentUser(viewModel: viewModel) // move here
    })
}

【讨论】：