SwiftUI: How do you restart a timer after cancelling it?

Question

I have a navigation view consisting of the main ContentView and a TimerView. The TimerView has a timer which correctly increments and also corr

Answer 1

To my knowledge (and historically), Timer cannot be restarted after cancellation or invalidation.

What I do is just re-declare the timer.

Here is an example with some added personal preferences:

struct TimerView: View {
    @State var secondsElapsed = 0
    @State var timer: Timer.TimerPublisher = Timer.publish (every: 1, on: .main, in: .common)
    var body: some View {
        VStack {
            Text("\(self.secondsElapsed) seconds elapsed")
            Button("Stop timer",
                   action: {
                    self.cancelTimer() // Just to be a little more DRY/maintenance-friendly, but personal preference.
            })
        }.onAppear(perform: {
            self.instantiateTimer() // You could also consider an optional self.timer variable.
            self.timer.connect() // This allows you to manually connect where you want with greater efficiency, if you don't always want to autostart.
        }).onDisappear(perform: {
            // I don't know your exact flow, but you said you want the timer to restart upon return navigation.  
            // So, I am just assuming you want to stop the timer when you navigate out.  
            // But, you can also easily remove this closure.
            // Also, this may not run as you would intuit.
            self.cancelTimer()
        }).onReceive(timer) { _ in
            self.secondsElapsed += 1
        }
    }

    func instantiateTimer() {
        self.timer = Timer.publish (every: 1, on: .main, in: .common)
        return
    }

    func cancelTimer() {
        self.timer.connect().cancel()
        return
    }
}