How can I pass Binding<Timer> in SwiftUI?

Question

I would like to pass a timer from ContentView to SecondView, but I don't know how to manage it because I never used it before.

Can someone figure this out for me?

ContentView

struct ContentView: View {
    @State private var timer = Timer.publish(every: 1, tolerance: 0.5, on: .main, in: .common).autoconnect()
    @State private var timeRemaining = 10
    
    
    var body: some View {
        NavigationView {
            VStack {
                Text("\(timeRemaining)")
                    .onReceive(timer) { _ in
                        if timeRemaining > 0 {
                            timeRemaining -= 1
                        }
                    }
                
                NavigationLink {
                    SecondView(timer: ???) // <-- What should i pass here?
                } label: {
                    Text("Change View")
                }
            }
        }
    }
}

SecondView

struct SecondView: View {
    @Binding var timer: ??? // <-- What type?
    @State private var timeRemaining = 5
    
    var body: some View {
        Text("Hello")
            .onReceive(timer) { _ in
                if timeRemaining > 0 {
                    timeRemaining -= 1
                }
            }
    }
}

struct SecondView_Previews: PreviewProvider {
    static var previews: some View {
        SecondView(timer: ???) // <-- Same thing here in SecondView preview
    }
}

Answer 1

With this timer declaration you are in the Combine world. Combine is the reactive framework from Apple.

First you would need to import it:

import Combine

I have commented the code but Combine is a far field and it probably would be best to read the documentation about it, read some tutorials and try some things out.

documentation

struct ContentView: View {
    // The typ here is Publishers.Autoconnect<Timer.TimerPublisher>
    // But we can erase it and the result will be a Publisher that emits a date and never throws an error: AnyPublisher<Date,Never>
    @State private var timer = Timer.publish(every: 1, tolerance: 0.5, on: .main, in: .common)
        .autoconnect()
        .eraseToAnyPublisher()
    @State private var timeRemaining = 10
    
    
    var body: some View {
        NavigationView {
            VStack {
                Text("\(timeRemaining)")
                    .onReceive(timer) { _ in
                        if timeRemaining > 0 {
                            timeRemaining -= 1
                        }
                    }
                
                NavigationLink {
                    // pass the publisher on
                    SecondView(timer: timer)
                } label: {
                    Text("Change View")
                }
            }
        }
    }
}

struct SecondView: View {
    //You don´t need binding here as this view never manipulates this publisher
    var timer: AnyPublisher<Date,Never>
    @State private var timeRemaining = 5
    
    var body: some View {
        Text("Hello")
            .onReceive(timer) { _ in
                if timeRemaining > 0 {
                    timeRemaining -= 1
                    print(timeRemaining)
                }
            }
    }
}

struct SecondView_Previews: PreviewProvider {
    // Creating a static private var should work here !not tested!
    @State static private var timer = Timer.publish(every: 1, tolerance: 0.5, on: .main, in: .common)
        .autoconnect()
        .eraseToAnyPublisher()
    static var previews: some View {
        SecondView(timer: timer)
    }
}