Ios swift – Possible concurrency issue with ForEach and array of @State in SwiftUI

I think what you are seeing is the natural behavior of async await the "actor" decides what to do and when to do it.

In this case the actor is juggling the timers and the UI updates.

Here are some things you can do to stabilize the while

1. Get rid of the Binding extension because Binding is not Sendable and therefore not safe to use inside async/await. You can turn on strict concurrency to see the warning. Binding by itself can introduce data races.

2. Use .task instead of Task so you can hold on to and stabilize the "timer".

3. Set the priority for the task it won’t be a perfect second but it should be much better. The await is a second but there are other lines of code so the true time is likely 1+ seconds.

    import SwiftUI

    struct TimerTestView: View {
        @State var first = MyStruct(setTime: 15)
        @State var second = MyStruct(setTime: 10)
        @State var third = MyStruct(setTime: 5)
        
        @State var array = [MyStruct(setTime: 15), MyStruct(setTime: 10), MyStruct(setTime: 5)]
        
        @State var hasNotAppearedYet = true
        @State private var date: Date = Calendar.current.date(byAdding: .second, value: 16, to: .init())!
        
        var body: some View {
            VStack { 
                Text(date, style: .timer) //Added an Apple timer to compare
                HStack { //Changed UI so I can see things side by side 
                    MyStructView(item: $array[0])
                    MyStructView(item: $first)
                }
                HStack {
                    MyStructView(item: $array[1])
                    MyStructView(item: $second)
                }
                HStack {
                    MyStructView(item: $array[2])
                    MyStructView(item: $third)
                }
            }
            .padding()
            
        }
    }

    struct MyStruct: Identifiable, Sendable {
        let id: UUID = .init()
        var setTime: Double
        var currentTime: Double = 0
    }


    #Preview {
        TimerTestView()
    }

    @MainActor
    struct MyStructView: View {
        @Binding var item: MyStruct
        var body: some View {
            Text("Seconds:n (item.currentTime)").padding().font(.title3)
            // Use the id to stabilize the task
                .task(id: item.id, priority: .userInitiated) { //Set the priority & hold on to the Task
                    do {
                        try await startTimer(name: item.id.uuidString)
                    } catch {
                        print(error)
                    }
                }
        }
        func startTimer(name: String) async throws { 
            let start = Date()
            item.currentTime = item.setTime
            print(name, item.currentTime)
            
            while (item.currentTime > 0) {
                try await Task.sleep(for: .seconds(1))
                try Task.checkCancellation()
                item.currentTime -= 1
                print(name, item.currentTime)
            }
        }
    }