When is NavigationService initialized?

Question

I want to catch the NavigationService.Navigating event from my Page, to prevent the user from navigating forward. I have an event handler defined thusly:

void Pr         


        

Answer 1

NavigationService.Navigate triggers both a NavigationService.Navigating event AND an Application.Navigating event. I solved this problem with the following:

public class PageBase : Page
{
    static PageBase()
    {
        Application.Current.Navigating += NavigationService_Navigating;
    }

    protected static void NavigationService_Navigating(object sender, NavigatingCancelEventArgs e)
    {
        // put your event handler code here...
    }
}

Answer 2

@Espo your link helped me find the workaround. I call it a workaround because it's ugly, but it's what MS themselves do in their documentation:

public MyPage() // ctor
{
    InitializeComponent();
    this.Loaded += delegate { NavigationService.Navigating += MyNavHandler; };
    this.Unloaded += delegate { NavigationService.Navigating -= MyNavHandler; };
}

So you basically have to unsubscribe from the navigation service's events when your page is unloaded.

+1 to your response for helping me find it. I don't seem to be able to mark my own response as the "accepted answer" so I guess I'll leave it for now.