How to update text using timer in SwiftUI

问题

I have text in view now i want to update that text using alert on every second.

Here is code i have done.

struct CountDownView : View {
    var body: some View {       
        VStack{
            Text("Update text with timer").lineLimit(nil).padding(20)

            }.navigationBarTitle(Text("WWDC"), displayMode:.automatic)
    }
}        

回答1:

Using Combine:

struct CurrentDateView : View {
    @State var now = Date()

    let timer = Timer.publish(every: 1, on: .current, in: .common).autoconnect()

    var body: some View {
        Text("\(now)")
            .onReceive(timer) {
                self.now = Date()
            }
    }
}

回答2:

i have managed to update text using alert.

i have declared date as State so whenever date is changed using alert text will also get updated.

struct CountDownView : View {

    @State var nowDate: Date = Date()
    let referenceDate: Date
    var timer: Timer {
        Timer.scheduledTimer(withTimeInterval: 1, repeats: true) {_ in 
            self.nowDate = Date()
        }
    }

    var body: some View {
        Text(countDownString(from: referenceDate))
            .font(.largeTitle)
            .onAppear(perform: {
                _ = self.timer
            })
    }

    func countDownString(from date: Date) -> String {
        let calendar = Calendar(identifier: .gregorian)
        let components = calendar
            .dateComponents([.day, .hour, .minute, .second],
                            from: nowDate,
                            to: referenceDate)
        return String(format: "%02dd:%02dh:%02dm:%02ds",
                      components.day ?? 00,
                      components.hour ?? 00,
                      components.minute ?? 00,
                      components.second ?? 00)
    }

}

来源：https://stackoverflow.com/questions/56504410/how-to-update-text-using-timer-in-swiftui