SwiftUI: How to cancel timer in SwiftUI view?

Question

I am using a timer in a SwiftUI view as in code below. It works as expected BUT under some conditions I want to cancel/stop that timer. There seems to be no ".cancel" property or method on the timer var. How do I cancel this timer? Any ideas/tips?


import SwiftUI

struct ContentView: View {

    @State private var selection = 2

    @State private var rotation: Double = GBstrtest

    let timer = Timer.publish (every: 0.8, on: .current, in: .common).autoconnect()

    var body: some View {
        TabView(selection: $selection){
            Text("Settings")
                .font(.title)
                .tabItem {
                    VStack {
                        Image(systemName: "gear")
                        .font(Font.system(.title ))
                        Text("Settings")
                    }
                }
                .tag(0)
            VStack {
                Divider().padding(2)
                ZStack {
                    Image("image1")
                        .resizable()
                        .aspectRatio(contentMode: .fit)
                    Image("image2")
                        .resizable()
                        .aspectRatio(contentMode:.fit)
                        .rotationEffect(.degrees(rotation))
                        .animation(.easeInOut(duration: 0.3) )
                        .padding(EdgeInsets(top: 0, leading: 50, bottom: 0, trailing: 50))
              }
              Spacer()
            }
            .tabItem {
                VStack {
                    Image(systemName: "speedometer")
                        .font(Font.system(.title ))
                    Text("Read Meter")
                }
            }
            .tag(1)
        }
        .onReceive(timer) {
            _ in self.rotation = Double.random(in: 0 ... 200)
            // How do I cancel timer HERE!?
        }
    }
}

Razib Mollick · Accepted Answer · 2019-09-29 15:37:20Z

68

Inside your conditional statement, use the following code:

self.timer.upstream.connect().cancel()

answered Sep 29, 2019 at 15:37

Razib Mollick

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5 Comments

SwiftiSwift Over a year ago

how to reconnect? @RazibMollick

GJ Nilsen Over a year ago

self.timer.upstream.autoconnect()

C0D3 Over a year ago

Yes to reconnect timer.upstream.autoconnect() works but your timer most likely should be a @State var since it is being reinitialized. If you used a 'let' for your timer like I was doing, autoconnect() won't work. Hope this helps.

Qazi Ammar Over a year ago

on reconnect it showing this warning Result of call to 'autoconnect()' is unused

Dan Over a year ago

For me timer.upstream.autoconnect() doesn't work even if it's declaired as @State private var timer ...

LNI · Accepted Answer · 2020-04-21 04:43:29Z

22

Full cycle goes like this:

struct MySwiftUIView : View {
...

@State var timer = Timer.publish (every: 1, on: .current, in: .common).autoconnect()
@State var timeRemaining = -1

var body: some View {
    ZStack {
       // Underlying shapes etc as needed

       Text("\(timeRemaining)").
           .opacity(timeRemaining > 0 ? 1 : 0)
           .onReceive(timer) { _ in
                if self.timeRemaining < 0 {
                    // We don't need it when we start off
                    self.timer.upstream.connect().cancel()
                    return
                }
                if self.timeRemaining > 0 {
                    self.timeRemaining -= 1
                } else {
                    self.timer.upstream.connect().cancel()
                    // Do the action on end of timer. Text would have been hidden by now
                }
          }
          .onTapGesture {  // Or any other event handler that should start countdown
                self.timeRemaining = Int(delayValue)
                self.timer = Timer.publish (every: 1, on: .current, in: 
                                                   .common).autoconnect()
          }
    }

Voila! A reusable timer, use it as many times as you'd like!

answered Apr 21, 2020 at 4:43

LNI

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1 Comment

Arton Hoxha Over a year ago

How can we achieve the same but with the logic and timer in ViewModel ?

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