fixed modal navigation

e2e/Maui/MauiModule/ViewModels/ViewAViewModel.cs

@@ -1,9 +1,17 @@
-namespace MauiModule.ViewModels;
+
+namespace MauiModule.ViewModels;
 
 public class ViewAViewModel : ViewModelBase
 {
     public ViewAViewModel(BaseServices baseServices) 
         : base(baseServices)
     {
     }
+
+    public bool CanNavigateResult { get; set; }
+
+    public override bool CanNavigate(INavigationParameters parameters)
+    {
+        return CanNavigateResult;
+    }
 }

e2e/Maui/MauiModule/ViewModels/ViewModelBase.cs

@@ -90,7 +90,7 @@ public void Initialize(INavigationParameters parameters)
             Messages.Add(parameter.Value.ToString());
     }
 
-    public void OnNavigatedFrom(INavigationParameters parameters)
+    public virtual void OnNavigatedFrom(INavigationParameters parameters)
     {
         Messages.Add("ViewModel NavigatedFrom");
     }

e2e/Maui/MauiModule/Views/ViewA.xaml

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8" ?>
+<?xml version="1.0" encoding="utf-8" ?>
 <ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
              xmlns:prism="http://prismlibrary.com"
              xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
@@ -8,6 +8,7 @@
              BackgroundColor="White">
   <Grid RowDefinitions="*,Auto"
         ColumnDefinitions="*,*">
+
     <CollectionView ItemsSource="{Binding Messages}"
                     Grid.ColumnSpan="2">
       <CollectionView.Header>
@@ -19,6 +20,11 @@
           <Label Text="Prism for .NET MAUI!"
                    HorizontalTextAlignment="Center"
                    Padding="0,0,0,20"/>
+          <StackLayout Orientation="Horizontal" >
+            <Label Text="Can Navigate Result:"/>
+            <CheckBox IsChecked="{Binding CanNavigateResult}" />
+          </StackLayout>
+
           <Label Text="Navigation Events:"
                  FontAttributes="Bold"
                  Padding="10,0"/>

e2e/Maui/PrismMauiDemo/MauiProgram.cs

@@ -49,17 +49,6 @@ public static MauiApp CreateMauiApp()
             //            .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))

src/Maui/Prism.Maui/Common/MvvmHelpers.cs

@@ -170,7 +170,7 @@ public static Task<bool> CanNavigateAsync(object page, INavigationParameters par
         return implementer.CanNavigateAsync(parameters);
     }
 
-    private static bool CanNavigate(object page, INavigationParameters parameters)
+    public static bool CanNavigate(object page, INavigationParameters parameters)
     {
         var implementer = GetImplementerFromViewOrViewModel<IConfirmNavigation>(page);
         return implementer?.CanNavigate(parameters) ?? true;
@@ -288,7 +288,7 @@ public static void SetCurrentPageDelegate(Func<Page, Page?> getCurrentPageDelega
         return EvaluateCurrentPage(page);
     };
 
-    private static Page? GetTarget(Page? target)
+    internal static Page? GetTarget(Page? target)
     {
         return target switch
         {

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

@@ -58,39 +58,6 @@ private Page GetRootPage(Page page) =>
                 _ => page
             };
 
-        /// <summary>
-        /// Handles the system back button press.
-        /// </summary>
-        [EditorBrowsable(EditorBrowsableState.Never)]
-        public void OnSystemBack()
-        {
-            var currentPage = CurrentPage;
-            if (currentPage?.Parent is NavigationPage navPage)
-            {
-                // The NavigationPage has already taken care of the GoBack
-                return;
-            }
-
-            var container = currentPage.GetContainerProvider();
-
-            if (IsRoot(currentPage))
-            {
-                var app = container.Resolve<IApplication>() as Application;
-                app.Quit();
-                return;
-            }
-            else if (currentPage is IDialogContainer dialogContainer)
-            {
-                if (dialogContainer.Dismiss.CanExecute(null))
-                    dialogContainer.Dismiss.Execute(null);
-            }
-            else if (PageNavigationService.NavigationSource == PageNavigationSource.Device)
-            {
-                var navigation = container.Resolve<INavigationService>();
-                navigation.GoBackAsync();
-            }
-        }
-
         internal bool IsRoot(Page page)
         {
             if (page == Page) return true;

src/Maui/Prism.Maui/Navigation/Xaml/NavigationExtensionBase.cs

@@ -1,4 +1,4 @@
-using System.Runtime.CompilerServices;
+using System.Runtime.CompilerServices;
 using System.Windows.Input;
 using Microsoft.Extensions.Logging;
 using Prism.Xaml;
@@ -67,7 +67,9 @@ protected virtual void Log(Exception ex, INavigationParameters parameters)
     protected void AddKnownNavigationParameters(INavigationParameters parameters)
     {
         parameters.Add(KnownNavigationParameters.Animated, Animated);
-        parameters.Add(KnownNavigationParameters.UseModalNavigation, UseModalNavigation);
+
+        if (UseModalNavigation.HasValue)
+            parameters.Add(KnownNavigationParameters.UseModalNavigation, UseModalNavigation);
     }
 
     protected override void OnPropertyChanged([CallerMemberName] string propertyName = null)
@@ -76,4 +78,4 @@ protected override void OnPropertyChanged([CallerMemberName] string propertyName
         if (propertyName == nameof(Page) || propertyName == nameof(IsNavigating))
             RaiseCanExecuteChanged();
     }
-}
+}

src/Maui/Prism.Maui/PrismAppBuilder.cs

@@ -58,14 +58,11 @@ internal PrismAppBuilder(IContainerExtension containerExtension, MauiAppBuilder
             {
                 android.OnBackPressed(activity =>
                 {
-                    var dialogModal = IDialogContainer.DialogStack.LastOrDefault();
-                    if (dialogModal is not null)
-                    {
-                        if (dialogModal.Dismiss.CanExecute(null))
-                            dialogModal.Dismiss.Execute(null);
-
-                        return true;
-                    }
+                    //the PrismWindow and PrismNavigationPage have their own back press logic and intercepts the hardware back button behavior
+                    //when this happens the PageNavigationService will take over and handle the navigation and decides whether to allow GoBack or not
+                    //this means we need to check if the PageNavigationService is handling the navigation and if it is, we need to prevent the OnBackPressed logic
+                    if (PageNavigationService.NavigationSource == PageNavigationSource.NavigationService)
+                        return true; 
 
                     var root = ContainerLocator.Container;
                     if (root is null)
@@ -78,13 +75,24 @@ internal PrismAppBuilder(IContainerExtension containerExtension, MauiAppBuilder
                     if (window is null)
                         return false;
 
-                    if(window.IsRootPage)
+                    //we are on the root page and the user pressed the hardward back button. the app has nowhere to navigation except to the background.
+                    //neither the PrismNavigationPage or the PrismWindow can handle this scenario, so we need to handle it here
+                    if (window.IsRootPage)
                     {
-                        return false;
+                        //when showing a dialog on the root page, if the user presses the hardware back button, we need to make sure the dialog
+                        //decides either to dismiss the dialog or keep it open
+                        var dialogModal = IDialogContainer.DialogStack.LastOrDefault();
+                        if (dialogModal is not null)
+                        {
+                            return true;
+                        }
+
+                        //note: if the PageNavigationService sends the android app to the background, this can cause the CanNavigate to be called twice.
+                        //if this becomes a problem, we may need to add an additional static flag to know when we are sending the app to the background to prevent the double call
+                        var canNavigate = MvvmHelpers.CanNavigate(MvvmHelpers.GetTarget(window.Page), new NavigationParameters());
+                        return !canNavigate;                        
                     }
 
-                    window.OnSystemBack();
-
                     return true;
                 });
             });

tests/Maui/Prism.Maui.Tests/Fixtures/Navigation/Xaml/GoBackExtensionFixture.cs

@@ -1,4 +1,4 @@
-using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging;
 using Microsoft.Maui.Controls;
 using Moq;
 using Prism.Common;
@@ -37,8 +37,6 @@ public void Execute_GoBackTypeDefault_GoesBackAPage()
     }
 
     [Theory]
-    [InlineData(true, null)]
-    [InlineData(false, null)]
     [InlineData(true, true)]
     [InlineData(false, true)]
     [InlineData(true, false)]

tests/Maui/Prism.Maui.Tests/Fixtures/Navigation/Xaml/NavigateToExtensionFixture.cs

@@ -1,4 +1,4 @@
-using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls;
 using Moq;
 using Prism.Common;
 using Prism.Maui.Tests.Mocks.Ioc;
@@ -57,8 +57,6 @@ public void Execute_NameIsSet_NavigatesToPage()
     }
 
     [Theory]
-    [InlineData(true, null)]
-    [InlineData(false, null)]
     [InlineData(true, true)]
     [InlineData(false, true)]
     [InlineData(true, false)]