在SwiftUI中使用NavigationButton和服务器请求

Question

How can I make a NavigationButton to wait for the server response before going to the next view ?

I've tried something like this

NavigationButton(destination: LogonView(),  onTrigger: { () -> Bool in
                    return self.viewModel.responseReceived
                }) {
                    Text("OK")
                    }.tapAction {
                        self.viewModel.fetch(companyID: &self.companyID)
                }

but the tapAction is never called.

I made it working using Button :

Button(action: {
        self.viewModel.fetch(companyID: &self.companyID)
    }) {
        Text("OK")
    }.presentation(viewModel.shouldPresentModal ? Modal(LogonView() : nil)

    // in ViewModel
    var shouldPresentModal = false { // set to true when data are received from server
            didSet {
                didChange.send(())
            }
        }

but I need to show the next view in a navigation, not modally

Thank you!

Answer 1

Sorin, at least in my understanding SwiftUI is designed only for the presentation layer, it's not supposed to replace your model. And it's "reactive", unlike UIKit, so making the view perform model-like actions is, by design, very hard.

I would approach the task like this :

class LoginModel : BindableObject {

    var didChange = PassthroughSubject<LoginModel, Never>()

    private(set) var username: String? {
        didSet {
            didChange.send(self)
        }
    }

    func load() {
        DispatchQueue.main.asyncAfter(deadline: .now() + 5.0) {
            self.username = "Sorin"
        }
    }
}

This is the model object encapsulating our login code. The async operation is here simulated by a simple delay.

And, then, the view :

public struct LoginScreen: View {

    @ObjectBinding var loginObject = LoginModel()

    public var body: some View {
        Group {
            if login.username == nil {
                Text("Trying to login, please wait...")
            } else {
                Text("Successful login, the username is \(loginObject.username!)")
            }
        }.onAppear {
            self.loginObject.load()
        }
    }
}

There are better ways of "linking" with the model object, but we're looking here only at a bare-bone example, obviously.

Your NavigationButton will only link to the LoginScreen, without any other code or trigger. The screen will initially display Trying to login, please wait... and after 5 sec will change to Successful login, the username is Sorin . Obviously you could go wild and replace my text here with anything you may want.