如何制作一个wpf倒数计时器？

I want to create wpf countdown timer that display the result as hh:mm:ss into textbox, I would be thankful for anyone help.

我想创建wpf倒数计时器，将结果显示为hh：mm：ss到文本框中，我会感谢任何人的帮助。

2 个解决方案

#1

You can use DispatcherTimer class (msdn).

您可以使用DispatcherTimer类（msdn）。

Duration of time you can hold in TimeSpan structure (msdn).

您可以在TimeSpan结构（msdn）中保留的持续时间。

If you want formatting TimeSpan to hh:mm:ss you should invoke ToString method with "c" argument (msdn).

如果要将TimeSpan格式化为hh：mm：ss，则应使用“c”参数（msdn）调用ToString方法。

Example:

例：

XAML:

XAML：

<Window x:Class="CountdownTimer.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <TextBlock Name="tbTime" />
    </Grid>
</Window>

Code-behind:

代码隐藏：

using System;
using System.Windows;
using System.Windows.Threading;

namespace CountdownTimer
{
    public partial class MainWindow : Window
    {
        DispatcherTimer _timer;
        TimeSpan _time;

        public MainWindow()
        {
            InitializeComponent();

            _time = TimeSpan.FromSeconds(10);

            _timer = new DispatcherTimer(new TimeSpan(0, 0, 1), DispatcherPriority.Normal, delegate
                {
                    tbTime.Text = _time.ToString("c");
                    if (_time == TimeSpan.Zero) _timer.Stop();
                    _time = _time.Add(TimeSpan.FromSeconds(-1));                    
                }, Application.Current.Dispatcher);

            _timer.Start();            
        }
    }
}

#2

There is nothing wrong with using DispatcherTimer for this purpose. However, IMHO the newer TPL-based async/await paradigm makes for code that is easier to write and read. It is also better to always use good MVVM practices for WPF programs, rather than to set UI element values directly from code-behind.

为此目的使用DispatcherTimer没有任何问题。但是，恕我直言，较新的基于TPL的异步/等待范例使得代码更易于编写和读取。最好始终为WPF程序使用良好的MVVM实践，而不是直接从代码隐藏设置UI元素值。

Here's an example of a program that implements a countdown-timer as described in the question, but using these more modern practices…

这是一个程序的例子，它实现了问题中描述的倒计时器，但使用了这些更现代的实践......

The view model is of course where the bulk of the interesting code resides, and even there the main thing is the single method _StartCountdown(), which implements the actual countdown:

视图模型当然是大部分有趣代码所在的位置，甚至主要的是单个方法_StartCountdown（），它实现了实际的倒计时：

ViewModel.cs:

ViewModel.cs：

class ViewModel
{
    private async void _StartCountdown()
    {
        Running = true;

        // NOTE: UTC times used internally to ensure proper operation
        // across Daylight Saving Time changes. An IValueConverter can
        // be used to present the user a local time.

        // NOTE: RemainingTime is the raw data. It may be desirable to
        // use an IValueConverter to always round up to the nearest integer
        // value for whatever is the least-significant component displayed
        // (e.g. minutes, seconds, milliseconds), so that the displayed
        // value doesn't reach the zero value until the timer has completed.

        DateTime startTime = DateTime.UtcNow, endTime = startTime + Duration;
        TimeSpan remainingTime, interval = TimeSpan.FromMilliseconds(100);

        StartTime = startTime;
        remainingTime = endTime - startTime;

        while (remainingTime > TimeSpan.Zero)
        {
            RemainingTime = remainingTime;
            if (RemainingTime < interval)
            {
                interval = RemainingTime;
            }

            // NOTE: arbitrary update rate of 100 ms (initialized above). This
            // should be a value at least somewhat less than the minimum precision
            // displayed (e.g. here it's 1/10th the displayed precision of one
            // second), to avoid potentially distracting/annoying "stutters" in
            // the countdown.

            await Task.Delay(interval);
            remainingTime = endTime - DateTime.UtcNow;
        }

        RemainingTime = TimeSpan.Zero;
        StartTime = null;
        Running = false;
    }

    private TimeSpan _duration;
    public TimeSpan Duration
    {
        get { return _duration; }
        set { _UpdateField(ref _duration, value); }
    }

    private DateTime? _startTime;
    public DateTime? StartTime
    {
        get { return _startTime; }
        private set { _UpdateField(ref _startTime, value); }
    }

    private TimeSpan _remainingTime;
    public TimeSpan RemainingTime
    {
        get { return _remainingTime; }
        private set { _UpdateField(ref _remainingTime, value); }
    }

    private bool _running;
    public bool Running
    {
        get { return _running; }
        private set { _UpdateField(ref _running, value, _OnRunningChanged); }
    }

    private void _OnRunningChanged(bool obj)
    {
        _startCountdownCommand.RaiseCanExecuteChanged();
    }

    private readonly DelegateCommand _startCountdownCommand;
    public ICommand StartCountdownCommand { get { return _startCountdownCommand; } }

    public ViewModel()
    {
        _startCountdownCommand = new DelegateCommand(_StartCountdown, () => !Running);
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void _UpdateField<T>(ref T field, T newValue,
        Action<T> onChangedCallback = null,
        [CallerMemberName] string propertyName = null)
    {
        if (EqualityComparer<T>.Default.Equals(field, newValue))
        {
            return;
        }

        T oldValue = field;

        field = newValue;
        onChangedCallback?.Invoke(oldValue);
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

As noted in the comments, the above will work as-is, but if you want specific output, it's useful to have IValueConverter implementations to adjust the output to suit user-specific needs. Here are some examples of those:

如评论中所述，上述内容将按原样运行，但如果您需要特定输出，则使用IValueConverter实现来调整输出以满足用户特定需求是有用的。以下是一些例子：

UtcToLocalConverter.cs:

UtcToLocalConverter.cs：

class UtcToLocalConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == null) return null;

        if (value is DateTime)
        {
            DateTime dateTime = (DateTime)value;

            return dateTime.ToLocalTime();
        }

        return Binding.DoNothing;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == null) return null;

        if (value is DateTime)
        {
            DateTime dateTime = (DateTime)value;

            return dateTime.ToUniversalTime();
        }

        return Binding.DoNothing;
    }
}

TimeSpanRoundUpConverter.cs:

TimeSpanRoundUpConverter.cs：

class TimeSpanRoundUpConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (!(value is TimeSpan && parameter is TimeSpan))
        {
            return Binding.DoNothing;
        }

        return RoundUpTimeSpan((TimeSpan)value, (TimeSpan)parameter);
    }

    private static TimeSpan RoundUpTimeSpan(TimeSpan value, TimeSpan roundTo)
    {
        if (value < TimeSpan.Zero) return RoundUpTimeSpan(-value, roundTo);

        double quantization = roundTo.TotalMilliseconds, input = value.TotalMilliseconds;
        double normalized = input / quantization;
        int wholeMultiple = (int)normalized;
        double fraction = normalized - wholeMultiple;

        return TimeSpan.FromMilliseconds((fraction == 0 ? wholeMultiple : wholeMultiple + 1) * quantization);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

And of course, some XAML to define the UI (where none of the UI elements have names, nor does the code-behind need to access any of them explicitly):

当然，还有一些XAML用于定义UI（其中没有UI元素具有名称，代码隐藏也不需要显式访问任何UI元素）：

MainWindow.xaml:

MainWindow.xaml：

<Window x:Class="TestSO16748371CountdownTimer.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:l="clr-namespace:TestSO16748371CountdownTimer"
        xmlns:s="clr-namespace:System;assembly=mscorlib"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
  <Window.DataContext>
    <l:ViewModel/>
  </Window.DataContext>

  <Window.Resources>
    <l:UtcToLocalConverter x:Key="utcToLocalConverter1"/>
    <l:TimeSpanRoundUpConverter x:Key="timeSpanRoundUpConverter1"/>
    <s:TimeSpan x:Key="timeSpanRoundTo1">00:00:01</s:TimeSpan>
  </Window.Resources>

  <Grid>
    <Grid.ColumnDefinitions>
      <ColumnDefinition Width="Auto"/>
      <ColumnDefinition/>
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
      <RowDefinition Height="Auto"/>
      <RowDefinition Height="Auto"/>
      <RowDefinition Height="Auto"/>
      <RowDefinition/>
    </Grid.RowDefinitions>

    <TextBlock Text="Duration: "/>
    <TextBox Text="{Binding Duration}" Grid.Column="1"/>

    <TextBlock Text="Start time:" Grid.Row="1"/>
    <TextBlock Text="{Binding StartTime, Converter={StaticResource utcToLocalConverter1}}" Grid.Row="1" Grid.Column="1"/>

    <TextBlock Text="Remaining time:" Grid.Row="2"/>
    <TextBlock Text="{Binding RemainingTime,
      StringFormat=hh\\:mm\\:ss,
      Converter={StaticResource timeSpanRoundUpConverter1},
      ConverterParameter={StaticResource timeSpanRoundTo1}}" Grid.Row="2" Grid.Column="1"/>

    <Button Content="Start Countdown" Command="{Binding StartCountdownCommand}" Grid.Row="3" VerticalAlignment="Top"/>

  </Grid>
</Window>