在尝试使用 Timer.scheduledTimer 的 SwiftUI 代码中获取未解析的标识符“self" [英] getting unresolved identifier 'self' in SwiftUI code trying to use Timer.scheduledTimer

问题描述

在 SwiftUI 中，我注意到使用一个定时器:

In SwiftUI I'm noting to use a Timer that:

尝试 1 - 这不能作为获取使用未解析的标识符‘自我’"

Try 1 - This doesn't work as get "Use of unresolved identifier 'self'"

var timer2: Timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) {
    self.angle = self.angle + .degrees(1)
}

尝试 2 - 有效，但必须输入_ = self.timer"才能稍后启动

Try 2 - Works, but have to put in an "_ = self.timer" to start it later

var timer: Timer {
    Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) {_ in
        self.angle = self.angle + .degrees(1)
    }
}
// then after need to use " .onAppear(perform: {_ = self.timer}) "

有没有办法让我的 Try1 工作?那是我可以在 SwiftUI 文件中预先创建计时器的地方吗?或者实际上在 SwiftUI 中的哪个位置通常会启动和停止计时器?即生命周期方法在哪里

Is there a way to get my Try1 working? That is where in a SwiftUI file I can create the timer up front? Or actually where in SwiftUI would one normally start and stop the timer? i.e. where are lifecycle methods

整个文件:

import SwiftUI

struct ContentView : View {

    @State var angle: Angle = .degrees(55)

//    var timer2: Timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) {
//        self.angle = self.angle + .degrees(1)
//    }

    var timer: Timer {
        Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) {_ in
            self.angle = self.angle + .degrees(1)
        }
    }

    private func buttonAction() {
        print("test")
        self.angle = self.angle + .degrees(5)
    }

    var body: some View {
        VStack{
            Text("Start")
            ZStack {
                Circle()
                    .fill(Color.blue)
                    .frame(
                        width: .init(integerLiteral: 100),
                        height: .init(integerLiteral: 100)
                    )
                Rectangle()
                    .fill(Color.green)
                    .frame(width: 20, height: 100)
                    // .rotationEffect(Angle(degrees: 25.0))
                    .rotationEffect(self.angle)
            }
            Button(action: self.buttonAction) {
                Text("CLICK HERE")
            }
            Text("End")
        }
         .onAppear(perform: {_ = self.timer})

    }
}

推荐答案

我不清楚您的示例是否需要一个计时器，但由于存在大量关于如何包含计时器的错误信息在 SwiftUI 应用中，我将进行演示.

It isn't clear to me that you need a timer for your example, but since there is a great deal of misinformation out there about how to include a Timer in a SwiftUI app, I'll demonstrate.

关键是把定时器放在别处，每次触发时发布.我们可以通过添加一个类来轻松地做到这一点，该类将计时器作为可绑定对象保存到我们的环境中(请注意，您需要导入 Combine):

The key is to put the timer elsewhere and publish each time it fires. We can easily do this by adding a class that holds the timer as a bindable object to our environment (note that you will need to import Combine):

class TimerHolder : BindableObject {
    var timer : Timer!
    let didChange = PassthroughSubject<TimerHolder,Never>()
    var count = 0 {
        didSet {
            self.didChange.send(self)
        }
    }
    func start() {
        self.timer?.invalidate()
        self.count = 0
        self.timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { 
            [weak self] _ in
            guard let self = self else { return }
            self.count += 1
        }
    }
}

我们需要通过环境向下传递这个类的实例，因此我们修改场景委托:

We will need to pass an instance of this class down through the environment, so we modify the scene delegate:

window.rootViewController = 
    UIHostingController(rootView: ContentView())

变成

window.rootViewController = 
    UIHostingController(rootView: ContentView()
        .environmentObject(TimerHolder()))

最后，让我们放一些启动计时器并显示计数的 UI，以证明它正在工作:

Finally, lets put up some UI that starts the timer and displays the count, to prove that it is working:

struct ContentView : View {
    @EnvironmentObject var timerHolder : TimerHolder
    var body: some View {
        VStack {
            Button("Start Timer") { self.timerHolder.start() }
            Text(String(self.timerHolder.count))
        }
    }
}

EDIT 为那些没有关注剧情的人更新:BindableObject 已经迁移到 ObservableObject，不再需要手动发送信号.所以:

EDIT Update for those who have not been following the plot: BindableObject has migrated into ObservableObject, and there is no need any more for manual signalling. So:

class TimerHolder : ObservableObject {
    var timer : Timer!
    @Published var count = 0
    // ... and the rest is as before ...

这篇关于在尝试使用 Timer.scheduledTimer 的 SwiftUI 代码中获取未解析的标识符“self"的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！