fixing Android hardware button

e2e/Maui/MauiModule/ViewModels/ViewModelBase.cs

@@ -3,7 +3,7 @@
 
 namespace MauiModule.ViewModels;
 
-public abstract class ViewModelBase : BindableBase, IInitialize, INavigatedAware, IPageLifecycleAware
+public abstract class ViewModelBase : BindableBase, IInitialize, INavigatedAware, IPageLifecycleAware, IConfirmNavigation
 {
     protected INavigationService _navigationService { get; }
     protected IPageDialogService _pageDialogs { get; }
@@ -109,4 +109,10 @@ public void OnDisappearing()
     {
         Messages.Add("View Disappearing");
     }
+
+    public virtual bool CanNavigate(INavigationParameters parameters)
+    {
+        Messages.Add("Can Navigate");
+        return true;
+    }
 }

e2e/Maui/PrismMauiDemo/MauiProgram.cs

@@ -38,21 +38,31 @@ public static MauiApp CreateMauiApp()
                     if (status == "Failed" && !string.IsNullOrEmpty(x.Result?.Exception?.Message))
                         Console.Error.WriteLine(x.Result.Exception.Message);
                 }))
-                //.CreateWindow(nav => nav.CreateBuilder()
-                //    .AddTabbedSegment(page =>
-                //        page.CreateTab("ViewC")
-                //            .CreateTab(t =>
-                //                t.AddNavigationPage()
-                //                 .AddSegment("ViewA", s => s.AddParameter("message", "Hello Tab - ViewA"))
-                //                 .AddSegment("ViewB", s => s.AddParameter("message", "Hello Tab - ViewB")))
-                //            //.CreateTab("ViewC", s => s.AddParameter("message", "Hello Tab - ViewC"))
-                //            .SelectedTab("NavigationPage|ViewB"))
-                //    .AddParameter("message_global", "This is a Global Message")
-                //    .Navigate())
-                //.CreateWindow("ViewA/ViewB/ViewC")
-                .CreateWindow(navigationService => navigationService.CreateBuilder()
-                    .AddSegment<SplashPageViewModel>()
-                    .NavigateAsync(HandleNavigationError))
+            //.CreateWindow(nav => nav.CreateBuilder()
+            //    .AddTabbedSegment(page =>
+            //        page.CreateTab("ViewC")
+            //            .CreateTab(t =>
+            //                t.AddNavigationPage()
+            //                 .AddSegment("ViewA", s => s.AddParameter("message", "Hello Tab - ViewA"))
+            //                 .AddSegment("ViewB", s => s.AddParameter("message", "Hello Tab - ViewB")))
+            //            //.CreateTab("ViewC", s => s.AddParameter("message", "Hello Tab - ViewC"))
+            //            .SelectedTab("NavigationPage|ViewB"))
+            //    .AddParameter("message_global", "This is a Global Message")
+            //    .Navigate())
+            //.CreateWindow("ViewA/ViewB") //broken
+            //.CreateWindow("NavigationPage/TabbedPage?createTab=ViewB/ViewC") //works
+            //.CreateWindow("ViewA/NavigationPage/TabbedPage?createTab=ViewB/ViewC") //works
+            //.CreateWindow(nav => nav
+            //    .CreateBuilder()
+            //    .AddTabbedSegment(page =>
+            //            page.CreateTab(t =>
+            //                t.AddNavigationPage()
+            //                 .AddSegment("ViewA")
+            //                 .AddSegment("ViewB")))
+            //    .NavigateAsync()) //works
+            .CreateWindow(navigationService => navigationService.CreateBuilder()
+                .AddSegment<SplashPageViewModel>()
+                .NavigateAsync(HandleNavigationError))
             )
             .ConfigureFonts(fonts =>
             {

src/Maui/Prism.Maui/Controls/PrismNavigationPage.cs

@@ -1,4 +1,4 @@
-using Prism.Common;
+using Prism.Common;
 using Prism.Navigation;
 using UIModalPresentationStyle = Microsoft.Maui.Controls.PlatformConfiguration.iOSSpecific.UIModalPresentationStyle;
 
@@ -12,34 +12,21 @@ public class PrismNavigationPage : NavigationPage
     /// <summary>
     /// Creates a new instance of the <see cref="PrismNavigationPage"/>
     /// </summary>
-    public PrismNavigationPage()
-    {
-        BackButtonPressed += HandleBackButtonPressed;
-    }
+    public PrismNavigationPage() { }
 
     /// <summary>
     /// Creates a new instance of the <see cref="PrismNavigationPage"/> with a specified <see cref="Page"/> at the Root
     /// </summary>
     /// <param name="page"></param>
     public PrismNavigationPage(Page page)
         : base(page)
-    {
-        BackButtonPressed += HandleBackButtonPressed;
-    }
+    { }
 
     /// <inheritdoc/>
-    public event EventHandler BackButtonPressed;
-
-    /// <inheritdoc/>
-    protected override bool OnBackButtonPressed()
-    {
-        BackButtonPressed.Invoke(this, EventArgs.Empty);
-        return false;
-    }
-
-    private async void HandleBackButtonPressed(object sender, EventArgs args)
+    protected sealed override bool OnBackButtonPressed()
     {
-        await MvvmHelpers.HandleNavigationPageGoBack(this);
+        MvvmHelpers.HandleNavigationPageGoBack(this).ConfigureAwait(false);
+        return true; //Prism will always handle the navigation
     }
 
 #if IOS

src/Maui/Prism.Maui/Navigation/PageNavigationService.cs

@@ -2,9 +2,7 @@
 using System.Web;
 using Prism.Common;
 using Prism.Events;
-using Prism.Extensions;
 using Prism.Mvvm;
-using Prism.Navigation.Regions;
 using Application = Microsoft.Maui.Controls.Application;
 using XamlTab = Prism.Navigation.Xaml.TabbedPage;
 
@@ -100,10 +98,6 @@ private async Task<INavigationResult> GoBackInternalAsync(INavigationParameters
             NavigationSource = PageNavigationSource.NavigationService;
 
             page = GetCurrentPage();
-            if (IsRoot(GetPageFromWindow(), page))
-            {
-                return SendAppToBackground(page);
-            }
 
             parameters.GetNavigationParametersInternal().Add(KnownInternalParameters.NavigationMode, NavigationMode.Back);
 
@@ -113,6 +107,11 @@ private async Task<INavigationResult> GoBackInternalAsync(INavigationParameters
                 throw new NavigationException(NavigationException.IConfirmNavigationReturnedFalse, page);
             }
 
+            if (IsRoot(GetPageFromWindow(), page))
+            {
+                return SendAppToBackground(page);
+            }
+
             bool useModalForDoPop = UseModalGoBack(page, parameters);
             Page previousPage = MvvmHelpers.GetOnNavigatedToTarget(page, Window?.Page, useModalForDoPop);
 
@@ -1249,6 +1248,8 @@ private bool GoBackModal(NavigationPage navPage)
             return true;
         else if (navPage.Parent is TabbedPage tabbed && tabbed != rootPage)
             return true;
+        else if (rootPage != navPage || IsRoot(rootPage, navPage.CurrentPage))
+            return true;
 
         return false;
     }

src/Maui/Prism.Maui/Navigation/PrismWindow.cs

@@ -84,14 +84,14 @@ public void OnSystemBack()
                 if (dialogContainer.Dismiss.CanExecute(null))
                     dialogContainer.Dismiss.Execute(null);
             }
-            else
+            else if (PageNavigationService.NavigationSource == PageNavigationSource.Device)
             {
                 var navigation = container.Resolve<INavigationService>();
                 navigation.GoBackAsync();
             }
         }
 
-        private bool IsRoot(Page page)
+        internal bool IsRoot(Page page)
         {
             if (page == Page) return true;
 

src/Maui/Prism.Maui/PrismAppBuilder.cs

@@ -78,11 +78,6 @@ internal PrismAppBuilder(IContainerExtension containerExtension, MauiAppBuilder
                     if (window is null)
                         return false;
 
-                    if (window.CurrentPage?.Parent is NavigationPage)
-                    {
-                        return true;
-                    }
-
                     if(window.IsRootPage)
                     {
                         return false;

tests/Maui/Prism.DryIoc.Maui.Tests/Fixtures/Navigation/NavigationTests.cs

@@ -5,8 +5,10 @@
 using Prism.DryIoc.Maui.Tests.Mocks.ViewModels;
 using Prism.DryIoc.Maui.Tests.Mocks.Views;
 using Prism.Navigation.Xaml;
+using Prism.Navigation;
 using Prism.Xaml;
 using TabbedPage = Microsoft.Maui.Controls.TabbedPage;
+using Microsoft.Maui.LifecycleEvents;
 
 namespace Prism.DryIoc.Maui.Tests.Fixtures.Navigation;
 
@@ -30,7 +32,7 @@ public void PagesInjectScopedInstanceOfIPageAccessor(string uri)
 
         var rootPage = window.Page;
 
-        if(rootPage is FlyoutPage flyoutPage)
+        if (rootPage is FlyoutPage flyoutPage)
         {
             TestPage(flyoutPage);
             rootPage = flyoutPage.Detail;
@@ -659,6 +661,53 @@ public void Navigate_And_SelectTab(string selectTab, Type viewType)
         Assert.IsType(viewType, child);
     }
 
+    [Fact]
+    public async Task Issue3123_GoBack_SendsAppToBackground()
+    {
+        var errorInvoked = false;
+        var mauiApp = CreateBuilder(prism => prism
+        .AddGlobalNavigationObserver(context => context.Subscribe(x =>
+        {
+            //this error message is used in this unit test to know that the SendAppToBackground method was called
+            //for Android we send the app to the background and do not throw the exception, otherwise we throw and quit the app
+            if (!x.Result.Success && x.Result?.Exception?.Message == NavigationException.CannotPopApplicationMainPage)
+                errorInvoked = true;
+        }))
+        .CreateWindow(nav => nav.CreateBuilder()
+            .AddTabbedSegment(page =>
+                    page.CreateTab(t =>
+                        t.AddNavigationPage()
+                            .AddSegment("MockViewA")
+                            .AddSegment("MockViewB")))
+            .NavigateAsync()))
+        .Build();
+        var window = GetWindow(mauiApp);
+
+        var tabbedPage = window.Page as TabbedPage;
+        Assert.NotNull(tabbedPage);
+
+        var currentPage = tabbedPage.CurrentPage;
+        Assert.IsType<PrismNavigationPage>(currentPage);
+        Assert.Equal(2, currentPage.Navigation.NavigationStack.Count);
+
+        var navPage = (PrismNavigationPage)currentPage;
+        Assert.IsType<MockViewB>(navPage.CurrentPage);
+
+        var container = navPage.CurrentPage.GetContainerProvider();
+        var navService = container.Resolve<INavigationService>();
+        await navService.GoBackAsync();
+
+        Assert.False(errorInvoked);
+        Assert.IsType<MockViewA>(navPage.CurrentPage);
+        Assert.Single(currentPage.Navigation.NavigationStack);
+
+        container = navPage.CurrentPage.GetContainerProvider();
+        navService = container.Resolve<INavigationService>();
+        await navService.GoBackAsync();
+
+        Assert.True(errorInvoked);
+    }
+
     private static void TestPage(Page page, bool ignoreNavigationPage = false)
     {
         Assert.NotNull(page.BindingContext);
@@ -671,7 +720,7 @@ private static void TestPage(Page page, bool ignoreNavigationPage = false)
         Assert.NotNull(accessor.Page);
         Assert.Same(page, accessor.Page);
 
-        if(page.Parent is not null)
+        if (page.Parent is not null)
         {
             Assert.False(page.BindingContext == page);
             Assert.False(page.BindingContext == page.Parent);
@@ -690,7 +739,7 @@ private static void TestPage(Page page, bool ignoreNavigationPage = false)
 
         if (page is TabbedPage tabbedPage)
         {
-            foreach(var child in tabbedPage.Children)
+            foreach (var child in tabbedPage.Children)
             {
                 TestPage(child, tabbedPage is MockExplicitTabbedPage);
 
@@ -734,7 +783,7 @@ private static void TestPageBehaviors(Page page)
 
         Assert.Equal(expectedBehaviors, page.Behaviors.Count);
 
-        switch(page)
+        switch (page)
         {
             case TabbedPage:
                 TestTabbedPageBehaviors(page);

tests/Maui/Prism.DryIoc.Maui.Tests/Prism.DryIoc.Maui.Tests.csproj

@@ -29,6 +29,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\..\src\Maui\Prism.DryIoc.Maui\Prism.DryIoc.Maui.csproj" />
+    <ProjectReference Include="..\..\..\src\Maui\Prism.Maui.Rx\Prism.Maui.Rx.csproj" />
   </ItemGroup>
 
 </Project>