Clearing backstack in NavigationService

I am navigating through different pages within my application. After I login, I come to home page from where the navigation starts. During navigation, when I come to homepage, I want to go to the login page by pressing BackKey but I can only navigate to previously navigated page. I could have overriden the BackKeyPress event to navigate to the Login Page but in LoginPage I should again override the Backkeypress otherwise there appears to be cycle between loginpage and homepage on backkey press. Is there anyway to clear the navigation history?

You can use NavigationService.RemoveBackEntry: http://msdn.microsoft.com/en-us/library/system.windows.navigation.navigationservice.removebackentry%28v=VS.92%29.aspx

For instance, to remove all entries from the stack:

while (this.NavigationService.BackStack.Any())
{
   this.NavigationService.RemoveBackEntry();
}

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Also, if you want to remove only the previous page after checking its URI:

var previousPage = this.NavigationService.BackStack.FirstOrDefault();

if (previousPage != null && previousPage.Source.ToString().StartsWith("/MainPage.xaml"))
{
    this.NavigationService.RemoveBackEntry();
}