Navbar back button override

Question

I need to override back button.There is OnBackButtonPressed() method but in android is working only for Hardware button! How to override also software navbar button ? I'm using the same page and I need to back in the previous state of that page (page views are changing by json file change)

Answer 1

You should go check out Xamarin Help's page about this since it lays out the many reason to fix your design as oppose to implementing something this way (such as displaying a NavigationPage using PushModalAsync instead of PushAsync).

Xamarin Help Link

I will also post a link to my other answer on a similar question that talks about another way to handle saving info on a page after the user clicks the back button if they choose to do so.

Link

But the Android gist of the answer from the Xamarin Help site is override OnOptionsItemSelected in your MainActivity (if you are not using a MasterDetailPage in your navigation, you will need to modify the var navPage... code below):

public override bool OnOptionsItemSelected(IMenuItem item)
{
    var app = Application.Current;
    if (item.ItemId == 16908332) // This makes me feel dirty.
    {
        var navPage = ((app.MainPage.Navigation.ModalStack[0] as MasterDetailPage).Detail as NavigationPage);

        if (app != null && navPage.Navigation.NavigationStack.Count > 0)
        {
            int index = navPage.Navigation.NavigationStack.Count - 1;

            var currentPage = navPage.Navigation.NavigationStack[index];

            var vm = currentPage.BindingContext as ViewModel;

            if (vm != null)
            {
                var answer = vm.OnBackButtonPressed();
                if (answer)
                    return true;
            }

        }
    }

    return base.OnOptionsItemSelected(item);
}