如何在SwiftUI中即时更新View? [英] How to make the View update instant in SwiftUI?

问题描述

我有一个 Text ，它用作计时器，具有不同的数组值.并显示 timerIntervalSinceNow .

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

问题是当它达到零时，它应该显示为零，但是在再次单击屏幕之前不会发生.如果我不单击它，它会一直上升，因为它是 timeIntervalSinceNow ，但是当我单击它时，它会以 0秒切换到 Text .

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.

是否有任何方法告诉SwiftUI自行执行此操作而无需单击?

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)
}

推荐答案

问题是 exerciseTime [value] 从不更改，因此视图不会重绘.

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

即使 exerciseTime [value] .timeIntervalSinceNow 可能有所不同，但实际的 exerciseTime [value] 仍保持不变.

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

我建议您使用带有 ObservableObject 的 Timer :

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
                }
            }
    }
}

并在您的视图中使用它:

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)
        }
    }
}

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