秒表 MVVM Xamarin 表单

Question

这是我第一次使用 xamarin 表单，我现在正在尝试为自己制作一个应用程序。在我的应用程序中，我在视图模型中创建了一个计时器，但秒数仅达到 59 并自动重置为 0。有谁知道我该如何解决这个问题以及如何在我的视图模型中制作停止按钮和重置按钮?

    public class TimerPageViewModel : ViewModelBase, INotifyPropertyChanged
    {
        Stopwatch stopwatch = new Stopwatch();
        private string _stopWatchHours;
        private string _stopWatchMinutes;
        private string _stopWatchSeconds;
        public TimerPageViewModel(INavigationService navigationService)
            : base(navigationService)
        {
            Title = "Timer";
            Start = new Command(OnStartTimerExecute);
            Stop = new Command(OnStop);
            Reset = new Command(onReset);
            StopWatchHours = stopwatch.Elapsed.Hours.ToString();
            StopWatchMinutes = stopwatch.Elapsed.Minutes.ToString();
            StopWatchSeconds = stopwatch.Elapsed.Seconds.ToString();
        }
        public string StopWatchHours
        {
            get { return _stopWatchHours; }
            set { _stopWatchHours = value; OnPropertyChanged("StopWatchHours"); }
        }
        public string StopWatchMinutes
        {
            get { return _stopWatchMinutes; }
            set { _stopWatchMinutes = value; OnPropertyChanged("StopWatchSeconds"); }
        }
        public string StopWatchSeconds
        {
            get { return _stopWatchSeconds; }
            set { _stopWatchSeconds = value; OnPropertyChanged("StopWatchSeconds"); }
        }
        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged(string propertyName)
        {
            var changed = PropertyChanged;
            if (changed != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
        public ICommand Start { get; set; }
        public ICommand Stop { get; set; }
        public ICommand Reset { get; set; }
        private void OnStartTimerExecute()
        {
            stopwatch.Start();
            Device.StartTimer(TimeSpan.FromSeconds(1), () =>
            {
                StopWatchHours = stopwatch.Elapsed.Hours.ToString();
                StopWatchMinutes = stopwatch.Elapsed.Minutes.ToString();
                StopWatchSeconds = stopwatch.Elapsed.Seconds.ToString();
                return true;
            });
        }
        private void OnStop()
        {
            stopwatch.Stop();
            stopwatch = null;
        }
        private void onReset()
        {
            stopwatch.Reset();
        }
    }   

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:prism="http://prismlibrary.com"
             prism:ViewModelLocator.AutowireViewModel="True"
             NavigationPage.HasNavigationBar="false"
             x:Class="MyApp.Views.TimerPage"
             IconImageSource="timer_icon_2x.png"
             Title="{Binding Title}">

    <StackLayout VerticalOptions="CenterAndExpand" HorizontalOptions="CenterAndExpand">
        <Label HorizontalOptions="Center" FontSize="45" TextColor="#00A8E8">
        <Label.FormattedText>
            <FormattedString>
                    <Span Text="{Binding StopWatchHours}"/>
                    <Span Text=":"/>
                    <Span Text="{Binding StopWatchMinutes}"/>
                    <Span Text=":"/>
                    <Span Text="{Binding StopWatchSeconds}"/>
                </FormattedString>
        </Label.FormattedText>
        </Label>
        <Button Command="{Binding Start}"/>
        <Button Command="{Binding Stop}"/>
        <Button Command="{Binding Reset}"/>
    </StackLayout>

</ContentPage>

Answer 1

您正在提高 OnPropertyChanged("StopWatchSeconds"); 而不是 OnPropertyChanged("StopWatchMinutes");

public string StopWatchMinutes
    {
        get { return _stopWatchMinutes; }
        set { _stopWatchMinutes = value; 
              OnPropertyChanged("StopWatchSeconds");
        }
    }