错误：实例方法“onReceive(_:perform:)”要求“Int”符合“Publisher”

Question

我现在有一个Text()基于10分钟的计时器（其改变600 seconds），格式9:59，9:58等等

下面的代码正在运行，但是现在我遇到了问题。我想在540 seconds( 9:00)处执行一个操作，所以我添加了：

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

但是，这给出了以下错误：

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

所以相反，我想在我的onReceive(self.countdown.secondsLeft)方法中添加剩余的秒数，如下所示 - 但 swift 不接受，self.countdown.secondsLeft因为它不是@Published Int：

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

然而，它是。

我的代码如下：

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)"
        
    }
}

倒计时.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()
    

} }

知道问题是什么吗？

Answer 1

@Zorgan 对于符合发布者错误的要求：

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

在 onReceive 的 Published 属性上添加 $

onReceive(self.countdown.$secondsLeft)

Answer 2

但这会产生以下错误：

尝试以下操作（通常可以修复此类错误）

if self.countdown.secondsLeft <= 540 && !codeSent {
    DispatchQueue.main.async { // << update state async
       self.codeSent = true
    }
}