Complete Concurrency check enabled and how to resolve warnings

Question

I am looking to resolve the concurrency warnings that I am getting after enabling the complete concurrency check in Xcode.

Here is a simple example to illustrate the warning. Consider I have a ContentView that has a long running task on the background thread. When I call the long running task inside that of a Task {...} I get a "Passing argument of non-sendable type 'ContentView' outside of main actor-isolated context may introduce data races" warning. I get this warning when I enable the concurrency settings to complete in Xcode. I tried the suggestion to make the ContentView Sendable but it generates additional warnings(see second image below) and will not work in my situation. How do I get around this? appreciate any help/direction

See code below:

struct ContentView: View {
    @State private var disable: Bool = false
    @State private var value: Double = 0

    var body: some View {
        VStack {
            Button {
                disable = true
            } label: {
                Text("Press")
            }
            .task {
                await value = self.fetchValue() //<---Here is the warning. See image below
            }
            Text("\(value)")

        }
    }
}

extension ContentView {
    
    func fetchValue() async -> Double {
        //long running task
        try? await Task.sleep(nanoseconds: 60)
        return 2.0
    }
}

Here is the warning:

Answer 1

A SwiftUI View is not attached to an actor the body is decorated with @MainActor but not the View itself.

When you have func in the View you can decorate the View with @MainActor the same way you would a "ViewModel".

import SwiftUI
@MainActor // Decorate the View
struct AsyncTest: View {
    @State private var isRunning: Bool = false
    @State private var value: Double = 0

    var body: some View {
        VStack {
            Button {
                print("press")
                isRunning = true
            } label: {
                Text("Press")
            }.disabled(isRunning)
                .task(id: isRunning) {
                    guard isRunning else {return}
                    print("start")
                    value = await fetchValue()
                    print("end")
                    isRunning = false
                }
            if isRunning {
                ProgressView()
            }
            
            Text("\(value)")

        }
    }
}

extension AsyncTest {
    
    func fetchValue() async -> Double {
        await Task.detached(priority: .userInitiated) {
            // Mock long runing task
            _ = (0...10000000).map { n in
                n.description
            }.sorted(using: KeyPathComparator(\.description))
            //long running task
            //try? await Task.sleep(nanoseconds: 60)
            return 2.0
        }.value
    }
}
#Preview {
    AsyncTest()
}