Async for-in loop

June 13, 2023

---

Use an asynchronous operation to update a SwiftUI Text view from a for-in loop. In this example, the step variable is updated for each iteration on the main thread. This allows the variable to update the Text view.

import SwiftUI

class Simulation: ObservableObject {

    @Published var step = 0
    let nsteps = 10

    func run() async {
        for n in 0..<nsteps {
            await MainActor.run {
                self.step = n
            }
            print("Running \(n) / \(nsteps)")
            sleep(2)
        }
    }
}

struct ContentView: View {

    @StateObject private var simulation = Simulation()

    var body: some View {
        VStack {
            Text("Running \(simulation.step + 1) / \(simulation.nsteps)")
            Button("Run simulation") {
                Task {
                    await simulation.run()
                }
            }
        }
        .padding()
        .frame(width: 400, height: 300)
    }
}