iOS 开发并发问题？

[0littleboy]

在编写用户列表模块中，后端需要并发的访问 users ，因此学了一段时间的并发，遇到了很多问题，解决了大部分，但仍然感觉代码似乎有不少问题，但由于水平不够，希望大家帮忙看看，感谢

actor UsersModel {
    private(set) var users: [User]
    private(set) var userIDs: Set<User.UserIDType>
    
    init() async {
//        users = Bundle.main.decode(file: "allUsers.json")
        userIDs = Set(["little-boy52", "0x3f", "mindexercise", "smilyt_", "zhui-ming-zhen-bai-1", "333"])
        // 升序排列
        users = (await loadAllUsers(userIDs: userIDs)).sorted { $0.contestResults?.rating ?? 0.0 > $1.contestResults?.rating ?? 0.0 }
    }
    
    func addUser(user: User) {
        
    }
    
    func addUserByID(id: User.UserIDType) async -> Bool {
        if let user = await loadUser(userid: id) {
            users.append(user)
            userIDs.insert(id)
            return true
        }
        return false
    }
    
    func deleteUser(user: User) {
        userIDs.remove(user.id)
        users.removeAll {
            return $0.id == user.id
        }
    }
    
    func contains(id: String) -> Bool {
        userIDs.contains(id)
    }
    
}

@MainActor
class UsersViewModel: ObservableObject {
    @Published var model: UsersModel? = nil
    
    func loadModel() async {
        let model = await UsersModel()
        DispatchQueue.main.async {
            // Update the UI on the main thread
            self.model = model
        }
    }
    
    var users: [User] {
        get async {
            if let model = model {
                return await model.users
            } else {
                return []
            }
        }
    }
    
    func addUser(user: User) async {
        await model?.addUser(user: user)
    }
    
    func addUserByID(id: User.UserIDType) async -> Bool {
        if model == nil {
            return false
        }
        return await model!.addUserByID(id: id)
    }
    
    func deleteUser(user: User) async {
        await model?.deleteUser(user: user)
    }
    
    func contains(id: String) async -> Bool {
        if model == nil {
            return false
        }
        return await model!.contains(id: id)
    }
}

最后调用 loadModel

// UsersView.swift

VStack {...}
.task {
    await usersVM.loadModel()
}

我在 UsersViewModel 中定义了计算字段 users，在 SwiftUI 中调用的话需要使用 ForEach(Task {await usersVM.users}.value) { user in ... }，但这样的话又会报错'async' property access in a function that does not support concurrency，如何解决？

[MakHoCheung]

好绕啊，简洁点就是
```
@State var users = []
VStack {...}
.task {
user = await usersVM.loadUsers()
}
```

[MakHoCheung]

class UsersViewModel: ObservableObject {
@Published var users = []

@MainActor
func addUsers(users : [User]) {
self.users = users
}
}

这种可以的，你并发拿 user 最后在 adduser 方法汇聚并切到主 actor