Question

在仔细检查Apple的SwiftUI文档，Web和stackoverflow之后，我似乎无法弄清楚如何使用多个类并在它们之间传递EnviromentObject数据。 SwiftUI的EnvironmentObject，ObservableObjects和Bindings上的所有文章都展示了如何将数据从模型传递到视图，但是如何从一个模型传递到另一个模型。还是我完全以错误的方式思考这个问题。

如何将@Published变量从A类传递到B类？

在这个简单的SwiftUI示例应用程序中，我试图将@Published数据从Settings类传递给NetworkManager类。此应用具有一个ContentView，其中包含两个用于用户名和密码的表单字段，并带有一个按钮，当按下该按钮时，它将与API联系并显示结果。

下面的代码将崩溃，因为NetworkManager mockService函数不知道什么是“设置”。我可以在View中读取观察到的“设置” EnvironmentObject，但是如何在另一个类中获取该数据呢？我猜这里与绑定有关，但不确定该怎么办。

场景代理：

...
var settings = Settings()
var networkManager = NetworkManager()

...
let contentView = ContentView()
    .environmentObject(settings)
    .environmentObject(networkManager)
...

ContentView.swift

class Settings: ObservableObject {
    @Published var username: String = ""
    @Published var password: String = ""    
}

// This function in reality will be rewritten and expanded with multiple networking calls
class NetworkManager: ObservableObject {
    @Published var token: String = ""

    func mockService() {
        token = settings.username + settings.password
    }
}

struct ContentView: View {
    @EnvironmentObject var settings: Settings
    @EnvironmentObject var networkManager: NetworkManager
    var body: some View {
        VStack {
            TextField("Username", text: $settings.username)
            TextField("Password", text: $settings.password)
            Button("Update"){
                self.networkManager.mockService()
            }
            Divider()
            Text("\(networkManager.token)")

        }
    }
}

Answer 1

这是让网络对象知道设置对象的一种方法，但我认为这不是最好的方法，你可以试试：

class Settings: ObservableObject {
    @Published var username: String = ""
    @Published var password: String = ""
    var currentSettingsPublisher: PassthroughSubject<Settings,Never> = .init()

    var cancellablesBag: Set<AnyCancellable> = []


    init() {
        observeChanges()
    }

    // Object will change is called to notify subscribers about changes( That's how swiftUI react to changes)
    private func observeChanges() {

        self.objectWillChange.sink { [weak self] (_) in
            guard let self = self else { return }
            self.currentSettingsPublisher.send(self)
        }.store(in: &cancellablesBag)
    }
}

// This function in reality will be rewritten and expanded with multiple networking calls
class NetworkManager: ObservableObject {
    
    @Published var token: String = ""
    var cancellablesBag: Set<AnyCancellable> = []
    var currentSettingsPublisher: AnyPublisher<Settings,Never>
    private var settings: Settings?

    init(_ settings: AnyPublisher<Settings,Never>) {
        self.currentSettingsPublisher = settings
        observeSettings()
    }

    func observeSettings() {
        currentSettingsPublisher
            // .debounce(for: .seconds(0.5), scheduler: RunLoop.main) maybe you can use debounce to debounce updating of your settings object
            .sink { [weak self] (newSettings) in
            guard let self = self else { return }
                print("i have the new settings")
            self.settings = newSettings
        }.store(in: &cancellablesBag)
    }
    

    
    func mockService() {
        guard let settings = settings else {
            return assertionFailure("Settings is nil, what to do ?")
        }

        token = settings.username + settings.password
        print("new token: \(token)")
    }
}

struct ContentView: View {
    @EnvironmentObject var settings: Settings
    @EnvironmentObject var networkManager: NetworkManager
    var body: some View {
        VStack {
            TextField("Username", text: $settings.username)
            TextField("Password", text: $settings.password)
            Button("Update"){
                self.networkManager.mockService()
            }
            Divider()
            Text("\(networkManager.token)")

        }
    }
}

和 SceneDelegate

var settings = Settings()
var networkManager: NetworkManager!

        func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {

networkManager = 
    NetworkManager(settings.currentSettingsPublisher.eraseToAnyPublisher())
            
    
            let contentView = ContentView()
                .environmentObject(settings)
                .environmentObject(networkManager)

}

Answer 2

您需要以这种方式在ContentView上声明您的ObservableObject：

@ObservedObject声明对符合ObservableObject协议的引用类型的依赖：它实现了objectWillChange属性以将更改发布到其数据中。

@ObservedObject var settings: Settings
@ObservedObject var networkManager: NetworkManager

SwiftUI在多个类之间传递数据

2 个答案: