How to make the View update instant in SwiftUI?

问题

I have a Text that acts as a timer with different values of my array. And it displays with timerIntervalSinceNow.

The problem is when it reaches zero it should show zero to but that does not happen before clicking again on the screen. If I do not click on it it keeps going up since it is timeIntervalSinceNow, but when I click it switches to the Text with 0 sec.

Any way on telling SwiftUI to do this by itself without clicking?

if(exerciseTime[value].timeIntervalSinceNow > 0) {
    Text(exerciseTime[value], style:.relative).foregroundColor(.white).font(.largeTitle).padding(.top, 30)                                   
} else {
    Text("0 sec").foregroundColor(.white).font(.largeTitle).padding(.top, 30)
}

回答1:

The issue is that exerciseTime[value] never changes, so the view is not redrawn.

Even though exerciseTime[value].timeIntervalSinceNow might be different, the actual exerciseTime[value] remains constant.

I recommend you use a Timer with an ObservableObject instead:

import Combine
import SwiftUI

class TimerViewModel: ObservableObject {
    private var timer: AnyCancellable?

    @Published var currentDate = Date()

    func start(endDate: Date) {
        timer = Timer.publish(every: 1.0, on: .main, in: .default)
            .autoconnect()
            .sink { [weak self] in
                guard let self = self else { return }
                self.currentDate = $0
                if self.currentDate >= endDate {
                    self.timer = nil
                }
            }
    }
}

and use it in your view:

struct TestView: View {
    @State private var exerciseTime = Calendar.current.date(byAdding: .second, value: 15, to: Date())!
    @StateObject private var timer = TimerViewModel()

    var body: some View {
        Group {
            if timer.currentDate < exerciseTime {
                Text(exerciseTime, style: .relative)
            } else {
                Text("0 sec")
            }
        }
        .foregroundColor(.white)
        .font(.largeTitle)
        .padding(.top, 30)
        .onAppear {
            timer.start(endDate: exerciseTime)
        }
    }
}

来源：https://stackoverflow.com/questions/65555911/how-to-make-the-view-update-instant-in-swiftui

标签

ios

swift

date

if-statement

swiftui