导航到其他页面后，如何在SwiftUI中恢复已发布的计时器? [英] How do I resume a published timer in SwiftUI after navigating to a different page?

问题描述

在下面的Playground示例中，UI会正确地使用当前日期进行更新，但是，当离开页面导航并返回时，计时器不会继续计时:

In the following Playground example, the UI updates with the current date correctly, however when navigating away from the page and coming back the timer does not resume ticking:

  import SwiftUI
  import PlaygroundSupport

  struct MainTabView: View {
    let timer = Timer.publish(every: 1, on: .main, in: .common)

    @State var time = Date()

    var body: some View {
        TabView {
            VStack {
                Text("\(time)").onReceive(self.timer) { self.time = $0 }
            }
            .onAppear { _ = self.timer.connect() }
            .tabItem {
                Text("Page 1")
            }

            Text("Page 2").tabItem {
                Text("Page 2")
            }

            Text("Page 3").tabItem {
                Text("Page 3")
            }
        }
    }
}

PlaygroundPage.current.setLiveView(MainTabView())

当页面开始显示时，如何使计时器重新开始更新?

How do I have the timer start updating again when the page starts showing?

我看到了一些解决方案，其中涉及将Timer包装到另一个类中，但是在View中无法执行任何操作.

I have seen solutions that involve wrapping the Timer in another class, but nothing that can be done in the View.

我认为在 onAppear {} 中的 connect()中进行调用会做到这一点.

I thought calling in connect() in onAppear {} would do it.

推荐答案

在onAppear内重新初始化计时器和日期将可行:

Reinitializing your timer and date inside the onAppear would work:

struct ContentView: View {
    @State private var timer = Timer.publish(every: 1, on: .main, in: .common)
    @State var time = Date()

    var body: some View {
        TabView {
            VStack {
                Text("\(time)").onReceive(self.timer) { self.time = $0 }
            }
            .onAppear(perform: {
                self.time = Date()
                self.timer = Timer.publish(every: 1, on: .main, in: .common)
                _ = self.timer.connect()
            })
            .tabItem {
                Text("Page 1")
            }

            Text("Page 2").tabItem {
                Text("Page 2")
            }

            Text("Page 3").tabItem {
                Text("Page 3")
            }
        }
    }
}

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