Can I use Swift async/await to call void methods in succession?

Question

In a ViewModel, I'm currently using callbacks to 1. make an API call and set data1, 2. use data1 in a second API call to set data2, then use data2 in a third function to parse and set a published value to be used in a View.

The examples I've seen so far have been based on awaiting return values. I only want to run void functions in succession. I've tried implementing the concept below but I keep getting "async in a function that does not support concurrency".

// ViewModel

var data1:Data?
var data2:Data?
@Published var myString:String?

func getFirstData() async -> Void {
  data1 = someAPIrequest()
}

func getSecondData() async -> Void {
  data2 = anotherAPIrequest(await data1)
}

func setViewString() {
  myString = data2!.name
}

// View

var body: some View {
  Text(await model.myString)
}.onAppear{
  getFirstData()
  getSecondData()
}

score 1 · Accepted Answer · answered Oct 25 '21 at 04:24

1

you could try something like this:

import SwiftUI

@main
struct TestApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

struct ContentView: View {
    @StateObject var model = MyDataModel()
    
    var body: some View {
        Text(model.myString ?? "")
            .task {
                await model.getFirstData()
                await model.getSecondData() // will wait for getFirstData to finish
                model.setViewString() // will wait for getSecondData to finish
            }
    }
}

class MyDataModel: ObservableObject {
    var data1: Data?
    var data2: Data?
    
    @Published var myString: String?
    
    func getFirstData() async -> Void {
        // just for testing
        self.data1 = "data1-data1-data1".data(using: .utf8)  // someAPIrequest()
    }
    
    func getSecondData() async -> Void {
        // just for testing
        data2 = data1  // anotherAPIrequest(data1)
    }
    
    func setViewString() {
        // just for testing
        myString = String(data: data2!, encoding: .utf8)
    }
}

answered Oct 25 '21 at 04:24

workingdog support Ukraine

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1

You've buried the most important part of your answer, which is that the `.task {` modifier is essentially `onAppear`, but it creates an asynchronous context. – jrturton Oct 25 '21 at 12:33
1

I should I unearth my `.task{...}` ? – workingdog support Ukraine Oct 25 '21 at 13:07
1

Yes! That's the useful part of your answer, that answers the actual question :) – jrturton Oct 25 '21 at 13:43
1

my comment was, how to make the `.task{...}` more prominent than showing it like I've done. – workingdog support Ukraine Oct 25 '21 at 22:19
1

You can add some text to your answer explaining what the problem is and how to fix it, at the moment you have code and no explanation – jrturton Oct 26 '21 at 10:10

Can I use Swift async/await to call void methods in succession?

1 Answers1