Make android back button work for navigation properly

critterfolio/CritterFolio/CritterFolio.Android/MainActivity.cs

@@ -1,7 +1,9 @@
-using Android.App;
+using System;
+using Android.App;
 using Android.Content.PM;
 using Avalonia;
 using Avalonia.Android;
+using Avalonia.Controls.ApplicationLifetimes;
 
 namespace CritterFolio.Android;
 
@@ -18,4 +20,22 @@ public class MainActivity : AvaloniaMainActivity<App>
         return base.CustomizeAppBuilder(builder)
             .WithInterFont();
     }
+
+    public override void OnBackPressed()
+    {
+        if (Sys.Navigation != null && Sys.Navigation.IsLastPage())
+        {
+            if (Avalonia.Application.Current?.ApplicationLifetime is ISingleViewApplicationLifetime lifetime)
+            {
+                //base.OnBackPressed();
+                // CA1422: This call site is reachable on: 'Android' 21.0 and later. 'AvaloniaActivity.OnBackPressed()' is obsoleted on: 'Android' 33.0 and later.
+                // Just call exit from Sytem.Environment for now which does not shutdown cleanly
+                Environment.Exit(0);
+            }
+        }
+        else
+        {
+            Sys.Navigation?.PopPage();
+        }
+    }
 }

critterfolio/CritterFolio/CritterFolio/Navigation.axaml.cs

@@ -33,6 +33,11 @@ public partial class Navigation : UserControl
         };
     }
 
+    public bool IsLastPage()
+    {
+        return _pageStack.Count == 1;
+    }
+
     public void Init(ContentControl pageContainer)
     {
         _pageContainer = pageContainer;
@@ -79,6 +84,7 @@ public partial class Navigation : UserControl
 
     public void PopPage()
     {
+        if (_pageStack.Count == 1) return;
         Console.WriteLine($"Removing page {CurrentPage?.Title ?? "??"} from the page stack");
         _pageStack.Pop();
         RefreshPage();