SwiftUI Timer 在更新 ObservedObjects 时不断重置

Question

我刚刚编写了一个简单的计时器代码，并试图找出一种方法，在其他观察到的对象状态发生变化时不重置计时器。当我使用 init 函数启动计时器时，只要其他观察到的对象的状态发生变化，它就会重置。当我用 onAppear 启动计时器时，一旦其他观察到的对象的状态发生变化，它就会发生变化，并且再也不会启动。我想要完成的是，计时器启动一次，并且在其他观察到的对象从其他 View 传递出去并且 tiemr 本身必须是 Subview 期间其他观察到的对象发生变化时不会重置。有什么建议吗？

import SwiftUI
import Combine
import Foundation

struct ContentView: View {

    @ObservedObject var apptCardVM: ApptCardViewModel
    @ObservedObject var timerData = TimerDataViewModel()

    var body: some View {
        VStack {
            CurrentDateView(timerData: timerData)  // << here !!

            Picker("Seizure Type", selection: $apptCardVM.typeIndex) {
            ForEach(0..<apptCardVM.typeChoice.count) {
                Text(self.apptCardVM.typeChoice[[=10=]])
            }
        }.pickerStyle(SegmentedPickerStyle())

        }

    }
}

struct CurrentDateView: View {
    @State private var currentDate = Date()
    let timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
    @ObservedObject var timerData: TimerDataViewModel
    var body: some View {

        Text("\(Int(timerData.hoursElapsed), specifier: "%02d"):\(Int(timerData.minutesElapsed), specifier: "%02d"):\(Int(timerData.secondsElapsed), specifier: "%02d")")
            .fontWeight(.bold)
            .textFieldStyle(RoundedBorderTextFieldStyle())
            .onAppear(){
                timerData.start()
            }
    }
}

class ApptCardViewModel: ObservableObject, Identifiable {
    @Published var typeChoice = ["Quick", "Long", "FullService"]
    @Published var typeIndex: Int = 0
    private var cancellables = Set<AnyCancellable>()


}

class TimerDataViewModel: ObservableObject{
    
    @Published var timer = Timer()
    @Published var startTime : Double = 0.0
    @Published var secondsOriginal = 0.0
    @Published var secondsElapsed = 0.0
    @Published var secondsElapsed_ = 0.0
    @Published var minutesElapsed = 0.0
    @Published var hoursElapsed = 0.0
    
    enum stopWatchMode {
        case running
        case stopped
        case paused
    }
    
    init(){
//        start()
        print("initialized")
    }

    
    func start(){
            self.secondsOriginal = self.startTime
            self.timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true){ timer in
                self.secondsOriginal += 1
                self.secondsElapsed_ = Double(Int(self.secondsOriginal))
                self.secondsElapsed = Double(Int(self.secondsOriginal)%60)
                self.minutesElapsed = Double(Int(self.secondsOriginal)/60 % 60)
                self.hoursElapsed = Double(Int(self.secondsOriginal)/3600 % 24)
            }
    }
}

Answer 1

import SwiftUI
import Combine
struct SeizureView: View {
    
    
    @ObservedObject var apptCardVM: ApptCardViewModel
    //This will solve your issue.
    @StateObject var timerData = TimerDataViewModel()
    @State private var currentDate = Date()
    var body: some View {
        VStack {
            CurrentDateView(currentDate: $currentDate, timerData: timerData)  
            //But something to consider
            //This View is reusable and does not need a timer. Just a Date object
            TimerView(date: currentDate, showSubseconds: false)
            Picker("Seizure Type", selection: $apptCardVM.typeIndex) {
                ForEach(0..<apptCardVM.typeChoice.count) {
                    Text(self.apptCardVM.typeChoice[[=10=]])
                }
            }.pickerStyle(SegmentedPickerStyle())
            
        }
        
    }
}

struct CurrentDateView: View {
    @Binding var currentDate : Date
    let timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
    @ObservedObject var timerData: TimerDataViewModel
    var body: some View {
        
        Text("\(Int(timerData.hoursElapsed), specifier: "%02d"):\(Int(timerData.minutesElapsed), specifier: "%02d"):\(Int(timerData.secondsElapsed), specifier: "%02d")")
            .fontWeight(.bold)
            .textFieldStyle(RoundedBorderTextFieldStyle())
            .onAppear(){
                timerData.start()
            }
    }
}

class ApptCardViewModel: ObservableObject, Identifiable {
    @Published var typeChoice = ["Quick", "Long", "FullService"]
    @Published var typeIndex: Int = 0
    private var cancellables = Set<AnyCancellable>()
    
    
}

class TimerDataViewModel: ObservableObject{
    
    @Published var timer = Timer()
    @Published var startTime : Double = 0.0
    @Published var secondsOriginal = 0.0
    @Published var secondsElapsed = 0.0
    @Published var secondsElapsed_ = 0.0
    @Published var minutesElapsed = 0.0
    @Published var hoursElapsed = 0.0
    
    enum stopWatchMode {
        case running
        case stopped
        case paused
    }
    
    init(){
        //        start()
        print("initialized")
    }
    
    
    func start(){
        self.secondsOriginal = self.startTime
        self.timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true){ timer in
            self.secondsOriginal += 1
            self.secondsElapsed_ = Double(Int(self.secondsOriginal))
            self.secondsElapsed = Double(Int(self.secondsOriginal)%60)
            self.minutesElapsed = Double(Int(self.secondsOriginal)/60 % 60)
            self.hoursElapsed = Double(Int(self.secondsOriginal)/3600 % 24)
        }
    }
}

struct TimerView: View {
    var date: Date
    var showSubseconds: Bool
    var fontWeight: Font.Weight = .bold
    
    var body: some View {
        if #available(watchOSApplicationExtension 8.0, watchOS 8.0, iOS 15.0, *) {
            //The code from here is mostly from https://developer.apple.com/wwdc21/10009
            TimelineView(MetricsTimelineSchedule(from: date)) { context in
                ElapsedTimeView(elapsedTime: -date.timeIntervalSinceNow, showSubseconds: showSubseconds)
            }
        } else {
            Text(date,style: .timer)
                .fontWeight(fontWeight)
                .clipped()
        }
    }
}
@available(watchOSApplicationExtension 8.0, watchOS 8.0, iOS 15.0,*)
private struct MetricsTimelineSchedule: TimelineSchedule {
    var startDate: Date
    
    init(from startDate: Date) {
        self.startDate = startDate
        
    }
    
    func entries(from startDate: Date, mode: TimelineScheduleMode) -> PeriodicTimelineSchedule.Entries {
        PeriodicTimelineSchedule(from: self.startDate, by: (mode == .lowFrequency ? 1.0 : 1.0 / 30.0))
            .entries(from: startDate, mode: mode)
    }
}
struct ElapsedTimeView: View {
    var elapsedTime: TimeInterval = 0
    var showSubseconds: Bool = false
    var fontWeight: Font.Weight = .bold
    @State private var timeFormatter = ElapsedTimeFormatter(showSubseconds: false)
    
    var body: some View {
        Text(NSNumber(value: elapsedTime), formatter: timeFormatter)
            .fontWeight(fontWeight)
            .onChange(of: showSubseconds) {
                timeFormatter.showSubseconds = [=10=]
            }
            .onAppear(perform: {
                timeFormatter = ElapsedTimeFormatter(showSubseconds: showSubseconds)
            })
    }
}

class ElapsedTimeFormatter: Formatter {
    let componentsFormatter: DateComponentsFormatter = {
        let formatter = DateComponentsFormatter()
        formatter.allowedUnits = [.minute, .second, .hour]
        formatter.zeroFormattingBehavior = .pad
        return formatter
    }()
    var showSubseconds: Bool
    init(showSubseconds: Bool) {
        self.showSubseconds = showSubseconds
        super.init()
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    override func string(for value: Any?) -> String? {
        guard let time = value as? TimeInterval else {
            return nil
        }
        
        guard let formattedString = componentsFormatter.string(from: time) else {
            return nil
        }
        
        if showSubseconds {
            let hundredths = Int((time.truncatingRemainder(dividingBy: 1)) * 100)
            let decimalSeparator = Locale.current.decimalSeparator ?? "."
            return String(format: "%@%@%0.2d", formattedString, decimalSeparator, hundredths)
        }
        
        return formattedString
    }
}
struct SeizureView_Previews: PreviewProvider {
    static var previews: some View {
        SeizureView(apptCardVM: ApptCardViewModel())
    }
}

SwiftUI Timer 在更新 ObservedObjects 时不断重置

SwiftUI Timer keep resetting when updating the ObservedObjects

timer

ios

swift

swiftui

observedobject