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。
答案 0 :(得分：24)
您可以使用DispatcherTimer班级（msdn）。
您可以在TimeSpan结构（msdn）中保留的持续时间。
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。
示例：
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>
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();
}
}
}
答案 1 :(得分：9)
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async / await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。
这是一个实现倒数计时器的程序示例，如问题中所述，但使用这些更现代的做法......
视图模型当然是大部分有趣的代码所在，即使主要的是单个方法_StartCountdown()，它实现了实际的倒计时：
<强> 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));
}
}
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IValueConverter实现调整输出以满足用户特定需求非常有用。以下是一些例子：
<强> 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;
}
}
<强> 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();
}
}
当然，有些XAML用于定义UI（其中没有UI元素具有名称，代码隐藏也不需要明确访问任何UI元素）：
<强> 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>