Silverlight : Response to Timer Events on the UI Thread

10/9/2010 4:42:15 PM
There are a few different timers you can use for triggering events at specific intervals, but recall that all UI updates must occur from the UI thread. You can always use BeginInvoke to marshal a delegate to the UI thread, but there’s a simpler way. WPF and Silverlight provide the DispatcherTimer class in the System.Windows.Threading namespace, which always fires on the UI thread. You can use this timer for updating the playback progress.
private System.Windows.Threading.DispatcherTimer timer =
new System.Windows.Threading.DispatcherTimer();

public MainPage()
//one second
timer.Interval = new TimeSpan(0,0,1);
timer.Tick += new EventHandler(timer_Tick);

void timer_Tick(object sender, EventArgs e)
switch (videoPlayer.CurrentState)
case MediaElementState.Playing:
case MediaElementState.Buffering:
if (videoPlayer.NaturalDuration.HasTimeSpan)
double total = videoPlayer.NaturalDuration.TimeSpan.TotalMilliseconds;
if (total > 0.0)
double elapsed = videoPlayer.Position.TotalMilliseconds;
100.0 * elapsed / total);
//do nothing


The DispatcherTimer is not Silverlight specific, and it can be used in any WPF app where you need a timer on the UI thread.

Figure 1 shows the video application with the progress bar in action.

Figure 1. Silverlight allows many of the same features of WPF, such as user controls.

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