Question

I have a page with “internal navigation”. That means that I show some list on that page and when user picks an item, I (download some data and) repopulate that list.

I made my own history stack, so when user wants to go back, I repopulate the list from history stack. User can go back by flicking or by clicking on hw back button.

Flicking works ok, but back button is weird.
I am canceling the back button event and instead I run my back navigation history. So I am still on the same page. BUT the back button click hides the application bar (even though I am canceling that event). And when I click it again and debug it, the ApplicationBar property is null.

// this overriden method causes ApplicationBar being hidden (or destroyed)
protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)
{
    e.Cancel = true;
    Messenger.Default.Send(...some notification here...); // this runs the internal navigation
    ApplicationBar.IsVisible = true; // this doesn't help and on the second try, it throws NullReferenceException
}

// this method is ok, repopulating is working without any problem
private void GestureListener_Flick(object sender, FlickGestureEventArgs e)
{
    Messenger.Default.Send( ...some notification here... ); // this run exactly same internal navigation
}

So question is – how to have ApplicationBar not destroyed/hidden? What is back button doing, when I cancel the navigation (it must do something with the AppBar)?

Answer 1

OK, this happens only when I use BindableApplicationBar and its Extensions (from here maxpaulousky.com).
It happens because Extensions handles back button event on page itself.

Solution was to check the Cancel property, and destroy it only when it’s false (in BindableApplicationBar class in the Extensions).