Controlling the Windows Phone 7 navigation service

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C#

Silverlight

Windows-Phone-7

Hi,
In my Windows Phone 7 app I have a timeline that plays and changes the content of a textbox to "ON". Basically when the textbox's content is "ON" and the user presses the hardware back button the timeline will stop playing and the user will not go back. However if the timeline is not playing and the user hits the back button I want them to go back.

here is my code so far:

protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)
         {
             if (txit.Text == "ON")
             {
                 txit.Text = "OFF";
                 camOUT.Stop();
             }
             else
             {
                 NavigationService.GoBack();
             }

         }

Thanks.