I have a function that runs in the main view model to listen for Auth Status changes and perform actions.

我有一个在主视图模型中运行的函数，用于监听Auth状态更改并执行操作。

class MainViewModel: ViewModel {

    private var cancellableSet: Set<AnyCancellable> = []

    override init() {
        super.init()
        
        // Listen for auth status changes
        Task(priority: .high) {
            await listenForAuthStatusChanges()
        }
    }
    
    
    // When auth status changes to true setup service
    @MainActor
    private func listenForAuthStatusChanges() async {
        SessionManager.shared.$isAuthenticated
            .receive(on: DispatchQueue.main)
            .sink { isAuthenticated in
                if isAuthenticated == true {
                    self.setupService()
                }
            }
            .store(in: &cancellableSet)
    }
    .../

SessionManager.isAuthenticated is a Published property

SessionManager.isAuthenticated是已发布的属性

@Published private(set) var isAuthenticated: Bool? = nil

If I remove @MainActor then I get an error Expression is 'async' but is not marked with 'await' and I have to add await before SessionManager.shared.$isAuthenticated to satisfy the error.

如果我删除@MainActor，则会得到一个错误表达式‘async’，但没有标记为‘aWait’，并且我必须在SessionManager.Shared之前添加aWait以满足该错误。

1. SessionManager.shared.$isAuthenticated is not an async function, it's a simple published property. Why would you have to await a published property?

   
   



2. What does @MainActor have to do with async/await and why does it's use negate the need for the await?

   
   

    private func listenForAuthStatusChanges() async {
        await SessionManager.shared.$isAuthenticated
            .receive(on: DispatchQueue.main)
            .sink { isAuthenticated in
                if isAuthenticated == true {
                    self.setupService()
                }
            }
            .store(in: &cancellableSet)
    }

I think I figured it out. SessionManager is a @MainActor which inherently makes the calling of all its methods and properties async, when called from a background context. By marking @MainActor on the caller, then both caller and callee are on the main thread.

我想我想通了。SessionManager是一个@MainActor，当从后台上下文调用时，它固有地使其所有方法和属性的调用同步。通过在调用方上标记@MainActor，则调用方和被调用方都在主线程上。

SessionManager.shared.$isAuthenticated is not an async function, it's a simple published property. Why would you have to await a published property?

It's not what because of what SessionManager is, it's because of what the context is. listenForAuthStatusChanges is an async method. Therefore the compiler takes over and enforces thread-safety. The await makes sure that two possibly conflicting things do not take place at the same time. You cannot talk to one actor from another without saying await.

这不是因为SessionManager是什么，而是因为上下文是什么。ListenForAuthStatusChanges是一个异步方法。因此，编译器接管并实施线程安全。等待确保两件可能相互冲突的事情不会同时发生。你不能不打招呼就和另一位演员交谈。

What does @MainActor have to do with async/await

It has everything to do with async/await. It is part of async/await. Or rather, they are both part of structured concurrency.

这与异步/等待有很大关系。它是异步/等待的一部分。或者，它们都是结构化并发的一部分。

why does it's use negate the need for the await

Because it guarantees that your code and the session manager code run on the same actor — namely the main actor. Now you are not talking to one actor from another, so await is not needed.

因为它保证了您的代码和会话管理器代码在同一个参与者上运行--即主参与者。现在，您不是在与一个演员与另一个演员交谈，因此不需要等待。