使用WPF MVVM实施和显示UI计时器

我有一个显示各种警报和状态的应用程序。某些警报在跳闸时应该显示一个计时器，该计时器从被激活的时间开始计时。我已经阅读了几种实现方法，甚至在这里都对SO提出了疑问，但似乎没有任何方法可以100％地起作用。

以下解决方案是最接近的。计时器显示并更新，但大约每30至45秒更新1秒。UI属性绑定到TimeElapsed属性，设置TimeStarted属性将启动所有操作。

 public class Alarm : INotifyPropertyChanged
 {
    DispatcherTimer timer = null;
    Stopwatch stopWatch = new Stopwatch();

    public Alarm()
    {
        Application.Current.Dispatcher.Invoke(() =>
        { 
            timer = new DispatcherTimer();
            timer.Tick += timer_Tick;
            timer.Interval = new TimeSpan(0, 0, 1);

        }, DispatcherPriority.Normal); 
    }

    private TimeSpan initialDifference;
    private DateTime? timeStarted;
    public DateTime? TimeStarted
    {
        get { return timeStarted; }
        set
        {
            // If the value is new
            if (timeStarted != value)
            {
                // If timeStarted was previously null then start the new timer
                if (!timeStarted.HasValue)
                {
                    timeStarted = value;

                    // Get the initial difference between Now and TimeStarted
                    initialDifference = DateTime.Now.Subtract(TimeStarted.Value);

                    //irolTimer = new System.Threading.Timer(TickTick, null, 1000, 1000);

                    Application.Current.Dispatcher.Invoke(() =>
                    {
                        stopWatch.Start();
                        timer.Start(); 
                    }, DispatcherPriority.Normal);

                }
                // If the timeStarted had a value but now its gone (stop the timer)
                else if (timeStarted.HasValue && value == null)
                {
                    if (stopWatch.IsRunning)
                        stopWatch.Stop();

                    timeStarted = value;
                }
                // If we already have a timer going but for some reason we just received a different start time
                else if (timeStarted.HasValue && value != null)
                {
                    timeStarted = value;

                    // Change the initial difference
                    initialDifference = DateTime.Now.Subtract(TimeStarted.Value);
                } 

                OnPropertyChanged("TimeStarted");
            }
        }
    }

    private string timeElapsed = string.Empty;
    public string TimeElapsed
    {
        get
        {
            return timeElapsed;
        }
        set
        {
            timeElapsed = value;
            OnPropertyChanged("TimeElapsed");
        }
    }

    void timer_Tick(object sender, EventArgs e)
    { 
        if (stopWatch.IsRunning)
        {
            TimeSpan elapsed = stopWatch.Elapsed;
            TimeSpan total = initialDifference + elapsed;

            TimeElapsed = String.Format("{0:00}:{1:00}:{2:00}", total.Hours, total.Minutes, total.Seconds / 10); 
        }
    }

 }

将Dispatcher.Invoke添加到Tick事件中会使计时器完全不显示。我尝试了几种不同的实现，包括使用没有运气的常规System.Threading.Timer。StopWatch似乎有些过分，我认为我可以通过以下操作完成相同的操作，但导致其停止工作：

  TimeElapsed = DateTime.Now.Subtract(TimeStarted.Value).ToString("hh:mm:ss");

这是一个屏幕截图，出于安全方面的考虑，我不得不对其进行编辑，但是我尝试将Text添加回上下文。用红色圈出的项目是计时器的文本。Xaml很简单，如下所示：

<StackPanel DockPanel.Dock="Left">
     <TextBlock FontSize="18" Text="{Binding Path=DisplayName, IsAsync=True}" Style="{StaticResource Alarm}" Foreground="White" FontWeight="Bold"  Padding="2,2,2,2" />
     <TextBlock Text="{Binding Path=TimeElapsed, IsAsync=True}" Foreground="White" FontSize="12" FontWeight="Bold" />   
 </StackPanel>