Error: Instance method 'onReceive(_:perform:)' requires that 'Int' conform to 'Publisher'

Question

I currently have a Text() which changes based on a 10 minute timer (600 seconds), in the format 9:59, 9:58 etc.

The below code was working, however now I'm facing a problem. I wanted to perform an action at 540 seconds (9:00), so I added:

if self.countdown.secondsLeft <= 540 && !codeSent {
    self.codeSent = true
}

however that gives the following error:

Modifying state during view update, this will cause undefined behavior.

So instead, I wanted to add the seconds left in my onReceive(self.countdown.secondsLeft) method as seen below - but swift doesn't accept self.countdown.secondsLeft as it's not a @Published Int:

Instance method 'onReceive(_:perform:)' requires that 'Int' conform to 'Publisher'

However, it is.

My code is below:

HomeView.swift

struct HomeView: View {
    @ObservedObject var waitingCountdown = CountDown(secondsLeft: 600)

    var body: some View {
            ZStack {
                WaitingTimer(countdown: self.waitingCountdown)
            }
    }

WaitingTimer.swift

struct WaitingTimer: View {
    @ObservedObject var countdown: CountDown
    @State var codeSent = false
    var body: some View {
        VStack{
            Text("\(timerText())")
                .font(.system(size: 28))
                .fontWeight(.bold)
                .foregroundColor(Color("Exit"))
                .frame(width: 80, height: 40)
                .padding(EdgeInsets(top: 3, leading: 10, bottom: 3, trailing: 10))
                .background(
                    Capsule()
                        .fill(Color.white)
                        .opacity(0.7)
                )
                .overlay(
                    Capsule()
                        .stroke(Color("Exit"), lineWidth: 2)
                )
                .onReceive(self.countdown.secondsLeft){
                    
                }
                .onAppear{
                    print("Start countdown")
                    self.countdown.start()
                }
                .onDisappear {
                    self.countdown.stop()
                }

        }.frame(minWidth: 0, maxWidth: .infinity, minHeight: 0, maxHeight: .infinity, alignment: .topLeading)
        .padding(.top, 30)
        .padding(.leading, 30)
    }
    
    func timerText() -> String{
        print("seconds left: \(self.countdown.secondsLeft) | codeSent: \(codeSent)")
        let minutes = Int( floor(Double(self.countdown.secondsLeft) / 60) )
        let _seconds = (self.countdown.secondsLeft) - (minutes * 60)
        if self.countdown.secondsLeft <= 540 && !codeSent {
            print("SECONDS LEFT: \(self.countdown.secondsLeft) | CODESENT: \(codeSent)")
            self.codeSent = true
        }
        // Show 9:09 instead of 9:9
        let seconds = _seconds < 1 ? "0\(_seconds)" : String(_seconds)
        print("Minutes \(minutes) Seconds left: \(seconds)")
        return "\(minutes):\(seconds)"
        
    }
}

CountDown.swift

class CountDown: ObservableObject {
    init(secondsLeft: Int){
        self.secondsLeft = secondsLeft
    }
    @Published var secondsLeft: Int
    var timer: Timer?
    func start(){
        print("start timer: \(self.secondsLeft)")
        self.timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true){ _ in
            self.secondsLeft -= 1
        }
    }
    func stop(){
        self.timer?.invalidate()
    

} }

Any idea what the problem is?

Answer 1

@Zorgan For the require that conform to publisher bug :

Instance method 'onReceive(_:perform:)' requires that 'Int' conform to 'Publisher'

add $ on your Published property in onReceive

onReceive(self.countdown.$secondsLeft)