delay region created and tracking of INavigationService

e2e/Forms/src/HelloRegions/ViewModels/RegionAViewModel.cs

@@ -1,10 +1,19 @@
-namespace HelloRegions.ViewModels
+using Prism.Navigation;
+using Prism.Regions.Navigation;
+
+namespace HelloRegions.ViewModels
 {
     public class RegionAViewModel : ViewModelBase
     {
-        public RegionAViewModel()
+        public RegionAViewModel(INavigationService navigationService, IRegionNavigationService regionNavigation)
         {
             Title = "Hello from Region A";
+            NavigationService = navigationService;
+            RegionNavigation = regionNavigation;
         }
+
+        public INavigationService NavigationService { get; set; }
+
+        public IRegionNavigationService RegionNavigation { get; set; }
     }
 }

src/Forms/Prism.Forms.Regions/Ioc/RegionRegistrationExtensions.cs

@@ -29,6 +29,7 @@ public static IContainerRegistry RegisterRegionServices(this IContainerRegistry
             containerRegistry.Register<IRegionNavigationJournalEntry, RegionNavigationJournalEntry>();
             containerRegistry.Register<IRegionNavigationJournal, RegionNavigationJournal>();
             containerRegistry.Register<IRegionNavigationService, RegionNavigationService>();
+            containerRegistry.RegisterManySingleton<RegionResolverOverrides>(typeof(IResolverOverridesHelper), typeof(IActiveRegionHelper));
             return containerRegistry.RegisterSingleton<IRegionManager, RegionManager>();
         }
 

src/Forms/Prism.Forms.Regions/Ioc/RegionResolverOverrides.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Prism.Navigation;
+using Prism.Regions;
+using Prism.Regions.Navigation;
+
+namespace Prism.Ioc
+{
+    internal class RegionResolverOverrides : IResolverOverridesHelper, IActiveRegionHelper
+    {
+        public IRegion ActiveRegion { get; set; }
+
+        public IEnumerable<(Type Type, object Instance)> GetOverrides()
+        {
+            if (ActiveRegion == null)
+            {
+                return Array.Empty<(Type Type, object Instance)>();
+            }
+
+            var overrides = new List<(Type Type, object Instance)>
+            {
+                (typeof(IRegionNavigationService), ActiveRegion.NavigationService)
+            };
+
+            if (ActiveRegion is INavigationServiceAware nsa && nsa.NavigationService != null)
+            {
+                overrides.Add((typeof(INavigationService), nsa.NavigationService));
+            }
+
+            return overrides;
+        }
+    }
+}

src/Forms/Prism.Forms.Regions/Regions/Behaviors/DelayedRegionCreationBehavior.cs

@@ -149,7 +149,13 @@ protected virtual IRegion CreateRegion(VisualElement targetElement, string regio
                 var regionAdapter = _regionAdapterMappings.GetMapping(targetElement.GetType());
                 var region = regionAdapter.Initialize(targetElement, regionName);
                 var cleanupBehavior = new RegionCleanupBehavior(region);
-                TargetElement.GetParentPage().Behaviors.Add(cleanupBehavior);
+                var page = targetElement.GetParentPage();
+                page.Behaviors.Add(cleanupBehavior);
+                if (region is INavigationServiceAware nsa)
+                {
+                    nsa.NavigationService = Prism.Navigation.Xaml.Navigation.GetNavigationService(page);
+                }
+
                 return region;
             }
             catch (Exception ex)

src/Forms/Prism.Forms.Regions/Regions/IActiveRegionHelper.cs

@@ -0,0 +1,7 @@
+namespace Prism.Regions
+{
+    internal interface IActiveRegionHelper
+    {
+        IRegion ActiveRegion { get; set; }
+    }
+}

src/Forms/Prism.Forms.Regions/Regions/INavigationServiceAware.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Prism.Navigation;
+
+namespace Prism.Regions
+{
+    internal interface INavigationServiceAware
+    {
+        INavigationService NavigationService { get; set; }
+    }
+}

src/Forms/Prism.Forms.Regions/Regions/Navigation/RegionNavigationContentLoader.cs

@@ -64,8 +64,10 @@ public object LoadContent(IRegion region, INavigationContext navigationContext)
                 return view;
             }
 
+            var activeRegion = _container.Resolve<IActiveRegionHelper>();
+            activeRegion.ActiveRegion = region;
             view = CreateNewRegionItem(candidateTargetContract) as VisualElement;
-
+            activeRegion.ActiveRegion = null;
             region.Add(view);
 
             return view;

src/Forms/Prism.Forms.Regions/Regions/Region.cs

@@ -4,6 +4,7 @@
 using System.Linq;
 using Prism.Ioc;
 using Prism.Mvvm;
+using Prism.Navigation;
 using Prism.Properties;
 using Prism.Regions.Behaviors;
 using Prism.Regions.Navigation;
@@ -14,7 +15,7 @@ namespace Prism.Regions
     /// <summary>
     /// Implementation of <see cref="IRegion"/> that allows multiple active views.
     /// </summary>
-    public class Region : BindableBase, IRegion
+    public class Region : BindableBase, IRegion, INavigationServiceAware
     {
         private ObservableCollection<ItemMetadata> _itemMetadataCollection;
         private IRegionManager _regionManager;
@@ -32,6 +33,13 @@ public Region()
             _sort = DefaultSortComparison;
         }
 
+        private WeakReference<INavigationService> _weakNavigationService;
+        INavigationService INavigationServiceAware.NavigationService
+        {
+            get => _weakNavigationService.TryGetTarget(out var target) ? target : null;
+            set => _weakNavigationService = new WeakReference<INavigationService>(value);
+        }
+
         private ViewsCollection _views;
         /// <summary>
         /// Gets a readonly view of the collection of views in the region.

src/Forms/Prism.Forms/Navigation/Xaml/Navigation.cs

@@ -72,7 +72,14 @@ private static void OnNavigationScopeChanged(BindableObject bindable, object old
         /// <param name="value">The Can Navigate value</param>
         public static void SetCanNavigate(BindableObject view, bool value) => view.SetValue(CanNavigateProperty, value);
 
-        internal static INavigationService GetNavigationService(Page page)
+        /// <summary>
+        /// Gets the instance of <see cref="INavigationService"/> for the given <see cref="Page"/>
+        /// </summary>
+        /// <param name="page">The <see cref="Page"/></param>
+        /// <returns>The <see cref="INavigationService"/></returns>
+        /// <remarks>Do not use... this is an internal use API</remarks>
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public static INavigationService GetNavigationService(Page page)
         {
             if(page == null) throw new ArgumentNullException(nameof(page));
 

src/Forms/Prism.Forms/PrismApplicationBase.cs

@@ -106,7 +106,9 @@ protected virtual void ConfigureViewModelLocator()
                 if(Container.IsRegistered<IResolverOverridesHelper>())
                 {
                     var resolver = Container.Resolve<IResolverOverridesHelper>();
-                    overrides.AddRange(resolver.GetOverrides());
+                    var resolverOverrides = resolver.GetOverrides();
+                    if(resolverOverrides.Any())
+                        overrides.AddRange(resolverOverrides);
                 }
 
                 if(!overrides.Any(x => x.Type == typeof(INavigationService)))