dispatcherTimer不重新启动

Question

我在我的应用程序中实现了倒计时

private async void Window_Activated(object sender, WindowActivatedEventArgs args)
{       
  dispatcherTimer = new DispatcherTimer();
  dispatcherTimer.Tick += dispatcherTimer_Tick;
  dispatcherTimer.Interval = new TimeSpan(0,1,0);
  dispatcherTimer.Start();     
}

private void dispatcherTimer_Tick(object sender, object e)
{
  TimeSpan timeSpan = new TimeSpan(blockTime.Hours, blockTime.Minutes, blockTime.Seconds);

  if (timeSpan != TimeSpan.Zero)
  {
    timeSpan = timeSpan.Subtract(TimeSpan.FromMinutes(1));
    Countdown_TexBlock.Text = String.Format("{0}:{1}", timeSpan.Hours, timeSpan.Minutes);
    dispatcherTimer.Start();   
  }     
  else
  {
    dispatcherTimer.Stop();
  }
}

代码工作，但只有一次，例如，我把15分钟的阻塞时间(倒计时将运行的时间)，在一分钟后，countdown.text将是0:14。

不应该用dispatcher.start()重新启动

Answer 1

在您发布的代码中，我没有看到blockTime变量在开始时被更改为任何其他值。这意味着，在dispatchTimer的每一个滴答中，timeSpan.Subtract表达式的值总是计算到相同的14分钟。在您的代码中，14分钟分配给一个本地可变值，在滴答结束时释放。这给出了dispatchTimer在没有发出Tick的情况下停止发布Tick的外观。

下面是我运行的工作原理(对于测试，我将分钟更改为秒，以便在合理的时间内观察到)。

public sealed partial class MainWindow : Window
{
    public MainWindow()
    {
        this.InitializeComponent();
        // Create the dispatch timer ONCE
        dispatcherTimer = new DispatcherTimer();
        dispatcherTimer.Tick += DispatcherTimer_Tick;
        dispatcherTimer.Interval = TimeSpan.FromSeconds(1);

        // This will restart the timer every
        // time the window is activated
        this.Activated += (sender, e) =>
        {
            startOrRestartDispatchTimer();
        };
    }

    private void startOrRestartDispatchTimer()
    {
        dispatcherTimer.Stop(); // If already running
        blockTime = TimeSpan.FromSeconds(15);
        Countdown_TexBlock.Text = blockTime.ToString();
        dispatcherTimer.Start();
    }

    private void DispatcherTimer_Tick(object sender, object e)
    {
        if (blockTime > TimeSpan.Zero)
        {
            blockTime = blockTime.Subtract(TimeSpan.FromSeconds(1));
            Countdown_TexBlock.Text = blockTime.ToString();
            if (blockTime == TimeSpan.Zero)
            {
                Countdown_TexBlock.Text = "Done";
                dispatcherTimer.Stop();
            }
        }
    }

    TimeSpan blockTime = TimeSpan.FromSeconds(15);

    private DispatcherTimer dispatcherTimer;

    // This will restart the timer when the button is clicked.
    private void buttonRestart_Click(object sender, RoutedEventArgs e) =>
        startOrRestartDispatchTimer();
}