TimeSpace结构的持续时间(msdn).

如果要格式化TimeSpan到hh：mm：ss,您应该使用“c”参数(msdn)调用ToString方法.

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(0,1),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();            
        }
    }
}