使用on appear将小时、分钟和秒全部加起来以设置@State。注意：把小时数乘以3600是错误的，所以我使用了一个额外的变量来修复我的机器上。

struct ContentView: View {
    @State var timeRemaining:Int = 0
    let timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
    var body: some View {
        HStack(spacing: 12) {
            timerStringView(timer: "\(hourString(timer: timeRemaining))")
            timerStringView(timer: "\(minutesString(timer: timeRemaining))")
            timerStringView(timer: "\(secondsString(timer: timeRemaining))")
        }
        .frame(width: 300, height: 34)
        .background(Color.gray)
        .onReceive(timer) { _ in
            if timeRemaining > 0 {
                timeRemaining -= 1
            } else {
                timer.upstream.connect().cancel()
            }
        }
        // Get the time
        .onAppear() {
            setTimer()
        }
    }
    
    func timerStringView(timer: String) -> some View {
        Text(timer)
            .font(.system(size: 18, weight: .bold))
            .foregroundColor(.black)
            .background(Color.white)
            .cornerRadius(6)
    }
    func hourString(timer: Int) -> String {
        let date = Date()
        let calendar = Calendar.current
        let hours = calendar.component(.hour, from: date)
        return String(format: "%02i", hours)
    }
    
    func minutesString(timer: Int) -> String {
        let date = Date()
        let calendar = Calendar.current
        let minutes = calendar.component(.minute, from: date)
        return String(format: "%02i", minutes)
    }
    
    func secondsString(timer: Int) -> String {
        let date = Date()
        let calendar = Calendar.current
        let second = calendar.component(.second, from: date)
        return String(format: "%02i", second)
    }
    func setTimer() {
        let date = Date()
        let calendar = Calendar.current
        let hours = calendar.component(.hour, from: date)
        let hourSeconds = hours * 3600
        let minuteSeconds = calendar.component(.minute, from: date) * 60
        let seconds = calendar.component(.second, from: date)
        timeRemaining = hourSeconds
        timeRemaining += minuteSeconds
        timeRemaining += seconds
    }
}