getting Region Navigation working

e2e/Forms/src/HelloRegions/Views/RegionDemoPage.xaml

@@ -11,7 +11,7 @@
     <ContentView prism:RegionManager.RegionName="ContentRegion" />
     <Button Text="Region A"
             Command="{Binding NavigateCommand}"
-            CommandParameter="RegionA" />
+            CommandParameter="RegionA?message=This%20is%20awesome!" />
     <Button Text="Region B"
             Command="{Binding NavigateCommand}"
             CommandParameter="RegionB" />

e2e/Forms/src/HelloWorld/App.xaml.cs

@@ -67,10 +67,11 @@ protected override void OnInitialized()
                 //behaviors.AddIfMissing(MyCustomBehavior.BehaviorName, typeof(MyCustomBehavior));
             });
 
-            this.ConfigureRegionAdapterMappings((mappings, container) =>
+            this.ConfigureRegionAdapterMappings(mappings =>
             {
                 // Demo purposes only... you could add aditional Adapter mappings here...
-                // mappings.RegisterMapping(typeof(RefreshView), container.Resolve<MyCustomAdapter>());
+
+                // mappings.RegisterMapping<RefreshView, MyCustomAdapter>();
             });
 
             NavigationService.NavigateAsync($"MyMasterDetail/MyTabbedPage").OnNavigationError(OnNavigationError);

src/Forms/Prism.Forms.Regions/Common/MvvmHelpers.cs

@@ -8,28 +8,51 @@ namespace Prism.Common
 {
     internal static class MvvmHelpers
     {
-        public static void ViewAndViewModelAction<T>(object view, Action<T> action) where T : class =>
-            PageUtilities.InvokeViewAndViewModelAction(view, action);
+        public static void ViewAndViewModelAction<T>(object view, Action<T> action)
+            where T : class
+        {
+            var stack = new System.Diagnostics.StackTrace();
+            if (view is T viewAsT)
+                action(viewAsT);
 
-        public static bool GetImplementerFromViewOrViewModel<T>(object view, out T implementer) where T : class =>
+            if (view is BindableObject bindable && bindable.BindingContext is T vmAsT)
+                action(vmAsT);
+        }
+
+        public static bool GetImplementerFromViewOrViewModel<T>(object view, out T implementer)
+            where T : class =>
             (implementer = GetImplementerFromViewOrViewModel<T>(view)) != null;
 
-        public static T GetImplementerFromViewOrViewModel<T>(object view) where T : class
+        public static T GetImplementerFromViewOrViewModel<T>(object view)
+            where T : class
         {
             if (view is T viewAsT)
             {
                 return viewAsT;
             }
 
-            if (view is VisualElement element)
+            if (view is VisualElement element && element.BindingContext is T vmAsT)
             {
-                var vmAsT = element.BindingContext as T;
                 return vmAsT;
             }
 
             return null;
         }
 
+        public static bool IsNavigationTarget(object view, INavigationContext navigationContext)
+        {
+            bool isViewTarget = false;
+            bool isVMTarget = false;
+
+            if (view is IRegionAware viewAsRegionAware)
+                isViewTarget = viewAsRegionAware.IsNavigationTarget(navigationContext);
+
+            if (view is BindableObject bindable && bindable.BindingContext is IRegionAware vmAsRegionAware)
+                isVMTarget = vmAsRegionAware.IsNavigationTarget(navigationContext);
+
+            return isViewTarget || isVMTarget;
+        }
+
         public static void OnNavigatedFrom(object view, INavigationContext navigationContext)
         {
             ViewAndViewModelAction<IRegionAware>(view, x => x.OnNavigatedFrom(navigationContext));

src/Forms/Prism.Forms.Regions/Common/ObservableObject.cs

@@ -3,13 +3,11 @@
 
 namespace Prism.Common
 {
+    // TODO: Refactor this... we probably do not need this for Xamarin
     /// <summary>
-    /// Class that wraps an object, so that other classes can notify for Change events. Typically, this class is set as 
-    /// a Dependency Property on DependencyObjects, and allows other classes to observe any changes in the Value. 
+    /// Class that wraps an object, so that other classes can notify for Change events. Typically, this class is set as
+    /// a Bindable Property on BindableObjects, and allows other classes to observe any changes in the Value.
     /// </summary>
-    /// <remarks>
-    /// This class is required, because in Silverlight, it's not possible to receive Change notifications for Dependency properties that you do not own. 
-    /// </remarks>
     /// <typeparam name="T">The type of the property that's wrapped in the Observable object</typeparam>
     public class ObservableObject<T> : BindableObject, INotifyPropertyChanged
     {

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

@@ -10,9 +10,9 @@ namespace Prism.Ioc
     public static class RegionNavigationRegistrationExtensions
     {
         /// <summary>
-        /// Registers a Page for navigation.
+        /// Registers a <see cref="View"/> for region navigation.
         /// </summary>
-        /// <typeparam name="TView">The Type of Page to register</typeparam>
+        /// <typeparam name="TView">The Type of <see cref="View"/> to register</typeparam>
         /// <param name="containerRegistry"><see cref="IContainerRegistry"/> used to register type for Navigation.</param>
         /// <param name="name">The unique name to register with the Page</param>
         public static void RegisterForNavigation<TView>(this IContainerRegistry containerRegistry, string name = null) 
@@ -27,9 +27,9 @@ public static void RegisterForNavigation<TView>(this IContainerRegistry containe
         }
 
         /// <summary>
-        /// Registers a Page for navigation.
+        /// Registers a <see cref="View"/> for region navigation.
         /// </summary>
-        /// <typeparam name="TView">The Type of Page to register</typeparam>
+        /// <typeparam name="TView">The Type of <see cref="View" to register</typeparam>
         /// <typeparam name="TViewModel">The ViewModel to use as the BindingContext for the Page</typeparam>
         /// <param name="name">The unique name to register with the Page</param>
         /// <param name="containerRegistry"></param>

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

@@ -1,4 +1,6 @@
 using System;
+using System.ComponentModel;
+using Prism.Behaviors;
 using Prism.Regions;
 using Prism.Regions.Adapters;
 using Prism.Regions.Behaviors;
@@ -46,14 +48,14 @@ public static PrismApplicationBase InitializeRegionConfigurations(this PrismAppl
         public static PrismApplicationBase ConfigureDefaultRegionBehaviors(this PrismApplicationBase app, Action<IRegionBehaviorFactory> configure = null)
         {
             var regionBehaviors = app.Container.Resolve<IRegionBehaviorFactory>();
-            regionBehaviors.AddIfMissing(BindRegionContextToVisualElementBehavior.BehaviorKey, typeof(BindRegionContextToVisualElementBehavior));
-            regionBehaviors.AddIfMissing(RegionActiveAwareBehavior.BehaviorKey, typeof(RegionActiveAwareBehavior));
-            regionBehaviors.AddIfMissing(SyncRegionContextWithHostBehavior.BehaviorKey, typeof(SyncRegionContextWithHostBehavior));
-            regionBehaviors.AddIfMissing(RegionManagerRegistrationBehavior.BehaviorKey, typeof(RegionManagerRegistrationBehavior));
-            regionBehaviors.AddIfMissing(RegionMemberLifetimeBehavior.BehaviorKey, typeof(RegionMemberLifetimeBehavior));
-            regionBehaviors.AddIfMissing(ClearChildViewsRegionBehavior.BehaviorKey, typeof(ClearChildViewsRegionBehavior));
-            regionBehaviors.AddIfMissing(AutoPopulateRegionBehavior.BehaviorKey, typeof(AutoPopulateRegionBehavior));
-            regionBehaviors.AddIfMissing(DestructibleRegionBehavior.BehaviorKey, typeof(DestructibleRegionBehavior));
+            regionBehaviors.AddIfMissing<BindRegionContextToVisualElementBehavior>(BindRegionContextToVisualElementBehavior.BehaviorKey);
+            regionBehaviors.AddIfMissing<RegionActiveAwareBehavior>(RegionActiveAwareBehavior.BehaviorKey);
+            regionBehaviors.AddIfMissing<SyncRegionContextWithHostBehavior>(SyncRegionContextWithHostBehavior.BehaviorKey);
+            regionBehaviors.AddIfMissing<RegionManagerRegistrationBehavior>(RegionManagerRegistrationBehavior.BehaviorKey);
+            regionBehaviors.AddIfMissing<RegionMemberLifetimeBehavior>(RegionMemberLifetimeBehavior.BehaviorKey);
+            regionBehaviors.AddIfMissing<ClearChildViewsRegionBehavior>(ClearChildViewsRegionBehavior.BehaviorKey);
+            regionBehaviors.AddIfMissing<AutoPopulateRegionBehavior>(AutoPopulateRegionBehavior.BehaviorKey);
+            regionBehaviors.AddIfMissing<DestructibleRegionBehavior>(DestructibleRegionBehavior.BehaviorKey);
 
             configure?.Invoke(regionBehaviors);
             return app;
@@ -69,14 +71,14 @@ public static PrismApplicationBase ConfigureRegionAdapterMappings(this PrismAppl
         {
             var container = app.Container;
             var regionAdapterMappings = container.Resolve<RegionAdapterMappings>();
-            regionAdapterMappings.RegisterMapping(typeof(CarouselView), container.Resolve<CarouselViewRegionAdapter>());
-            regionAdapterMappings.RegisterMapping(typeof(CollectionView), container.Resolve<CollectionViewRegionAdapter>());
-            regionAdapterMappings.RegisterMapping(typeof(FlexLayout), container.Resolve<LayoutViewRegionAdapter>());
-            regionAdapterMappings.RegisterMapping(typeof(StackLayout), container.Resolve<LayoutViewRegionAdapter>());
-            regionAdapterMappings.RegisterMapping(typeof(ScrollView), container.Resolve<ScrollViewRegionAdapter>());
-            regionAdapterMappings.RegisterMapping(typeof(ContentView), container.Resolve<ContentViewRegionAdapter>());
-            regionAdapterMappings.RegisterMapping(typeof(Frame), container.Resolve<ContentViewRegionAdapter>());
-            regionAdapterMappings.RegisterMapping(typeof(RefreshView), container.Resolve<ContentViewRegionAdapter>());
+            regionAdapterMappings.RegisterMapping<CarouselView, CarouselViewRegionAdapter>();
+            regionAdapterMappings.RegisterMapping<CollectionView, CollectionViewRegionAdapter>();
+            regionAdapterMappings.RegisterMapping<FlexLayout, LayoutViewRegionAdapter>();
+            regionAdapterMappings.RegisterMapping<StackLayout, LayoutViewRegionAdapter>();
+            regionAdapterMappings.RegisterMapping<ScrollView, ScrollViewRegionAdapter>();
+            regionAdapterMappings.RegisterMapping<ContentView, ContentViewRegionAdapter>();
+            regionAdapterMappings.RegisterMapping<Frame, ContentViewRegionAdapter>();
+            regionAdapterMappings.RegisterMapping<RefreshView, ContentViewRegionAdapter>();
 
             configure?.Invoke(regionAdapterMappings);
             return app;

src/Forms/Prism.Forms.Regions/Properties/AssemblyInfo.cs

@@ -0,0 +1,3 @@
+using Xamarin.Forms;
+
+[assembly: XmlnsDefinition("http://prismlibrary.com", "Prism.Regions.Xaml")]

src/Forms/Prism.Forms.Regions/Regions/Adapters/RegionAdapterBase.cs

@@ -82,11 +82,11 @@ protected virtual void AttachDefaultBehaviors(IRegion region, T regionTarget)
                     {
                         IRegionBehavior behavior = behaviorFactory.CreateFromKey(behaviorKey);
 
-                        if (regionTarget is VisualElement dependencyObjectRegionTarget)
+                        if (regionTarget is VisualElement visualElementRegionTarget)
                         {
                             if (behavior is IHostAwareRegionBehavior hostAwareRegionBehavior)
                             {
-                                hostAwareRegionBehavior.HostControl = dependencyObjectRegionTarget;
+                                hostAwareRegionBehavior.HostControl = visualElementRegionTarget;
                             }
                         }
 
@@ -137,7 +137,7 @@ private static void SetObservableRegionOnHostingControl(IRegion region, T region
                 // Set the region as a dependency property on the control hosting the region
                 // Because we are using an observable region, the hosting control can detect that the
                 // region has actually been created. This is an ideal moment to hook up custom behaviors
-                RegionManager.GetObservableRegion(targetElement).Value = region;
+                Xaml.RegionManager.GetObservableRegion(targetElement).Value = region;
             }
         }
     }

src/Forms/Prism.Forms.Regions/Regions/Adapters/RegionAdapterMappings.cs

@@ -16,42 +16,19 @@ public class RegionAdapterMappings
         /// <summary>
         /// Registers the mapping between a type and an adapter.
         /// </summary>
-        /// <param name="controlType">The type of the control.</param>
-        /// <param name="adapter">The adapter to use with the <paramref name="controlType"/> type.</param>
-        /// <exception cref="ArgumentNullException">When any of <paramref name="controlType"/> or <paramref name="adapter"/> are <see langword="null" />.</exception>
-        /// <exception cref="InvalidOperationException">If a mapping for <paramref name="controlType"/> already exists.</exception>
-        public void RegisterMapping(Type controlType, IRegionAdapter adapter)
+        /// <typeparam name="TControl">The type of the control</typeparam>
+        /// <typeparam name="TAdapter">The type of the IRegionAdapter to use with the TControl</typeparam>
+        public void RegisterMapping<TControl, TAdapter>() where TAdapter : IRegionAdapter
         {
-            if (controlType == null)
-                throw new ArgumentNullException(nameof(controlType));
-
-            if (adapter == null)
-                throw new ArgumentNullException(nameof(adapter));
+            var controlType = typeof(TControl);
 
             if (mappings.ContainsKey(controlType))
                 throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture,
                                                                   Resources.MappingExistsException, controlType.Name));
 
-            mappings.Add(controlType, adapter);
-        }
+            var adapter = ContainerLocator.Container.Resolve<TAdapter>();
 
-        /// <summary>
-        /// Registers the mapping between a type and an adapter.
-        /// </summary>
-        /// <typeparam name="TControl">The type of the control</typeparam>
-        public void RegisterMapping<TControl>(IRegionAdapter adapter)
-        {
-            RegisterMapping(typeof(TControl), adapter);
-        }
-
-        /// <summary>
-        /// Registers the mapping between a type and an adapter.
-        /// </summary>
-        /// <typeparam name="TControl">The type of the control</typeparam>
-        /// <typeparam name="TAdapter">The type of the IRegionAdapter to use with the TControl</typeparam>
-        public void RegisterMapping<TControl, TAdapter>() where TAdapter : IRegionAdapter
-        {
-            RegisterMapping(typeof(TControl), ContainerLocator.Container.Resolve<TAdapter>());
+            mappings.Add(controlType, adapter);
         }
 
         /// <summary>

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

@@ -25,7 +25,7 @@ public class ClearChildViewsRegionBehavior : RegionBehavior
             BindableProperty.CreateAttached("ClearChildViews", typeof(bool), typeof(ClearChildViewsRegionBehavior), false);
 
         /// <summary>
-        /// Gets the ClearChildViews attached property from a DependencyObject.
+        /// Gets the ClearChildViews attached property from a BindableObject.
         /// </summary>
         /// <param name="target">The object from which to get the value.</param>
         /// <returns>The value of the ClearChildViews attached property in the target specified.</returns>
@@ -38,7 +38,7 @@ public static bool GetClearChildViews(BindableObject target)
         }
 
         /// <summary>
-        /// Sets the ClearChildViews attached property in a DependencyObject.
+        /// Sets the ClearChildViews attached property in a BindableObject.
         /// </summary>
         /// <param name="target">The object in which to set the value.</param>
         /// <param name="value">The value of to set in the target object's ClearChildViews attached property.</param>
@@ -64,7 +64,7 @@ private static void ClearChildViews(IRegion region)
             {
                 if (GetClearChildViews(view))
                 {
-                    view.ClearValue(RegionManager.RegionManagerProperty);
+                    view.ClearValue(Xaml.RegionManager.RegionManagerProperty);
                 }
             }
         }

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

@@ -20,13 +20,15 @@ namespace Prism.Regions.Behaviors
     /// </remarks>
     public class DelayedRegionCreationBehavior
     {
+        private static readonly ICollection<DelayedRegionCreationBehavior> _instanceTracker =
+            new Collection<DelayedRegionCreationBehavior>();
+
         private readonly RegionAdapterMappings _regionAdapterMappings;
+        private readonly object _trackerLock = new object();
+
         private WeakReference _elementWeakReference;
         private bool _regionCreated = false;
 
-        private static ICollection<DelayedRegionCreationBehavior> _instanceTracker = new Collection<DelayedRegionCreationBehavior>();
-        private object _trackerLock = new object();
-
         /// <summary>
         /// Initializes a new instance of the <see cref="DelayedRegionCreationBehavior"/> class.
         /// </summary>
@@ -45,7 +47,7 @@ public DelayedRegionCreationBehavior(RegionAdapterMappings regionAdapterMappings
         /// so this behavior can be tested in isolation.
         /// </summary>
         /// <value>The region manager accessor.</value>
-        public IRegionManagerAccessor RegionManagerAccessor { get; set; }
+        public IRegionManagerAccessor RegionManagerAccessor { get; }
 
         /// <summary>
         /// The element that will host the Region.
@@ -76,15 +78,6 @@ public void Detach()
             UnWireTargetElement();
         }
 
-#if false
-#region NeedToRemove
-
-        private void WireUpTargetElement() { }
-        private void UnWireTargetElement() { }
-
-#endregion
-#endif
-
         /// <summary>
         /// Called when the <see cref="IRegionManager"/> is updating it's <see cref="IRegionManager.Regions"/> collection.
         /// </summary>
@@ -132,8 +125,8 @@ protected virtual IRegion CreateRegion(VisualElement targetElement, string regio
             try
             {
                 // Build the region
-                IRegionAdapter regionAdapter = this._regionAdapterMappings.GetMapping(targetElement.GetType());
-                IRegion region = regionAdapter.Initialize(targetElement, regionName);
+                var regionAdapter = _regionAdapterMappings.GetMapping(targetElement.GetType());
+                var region = regionAdapter.Initialize(targetElement, regionName);
 
                 return region;
             }
@@ -147,19 +140,6 @@ private void WireUpTargetElement()
         {
             TargetElement.PropertyChanged += TargetElement_ParentChanged;
             Track();
-            //var element = TargetElement;
-            //if (element != null)
-            //{
-            //    element.Loaded += this.ElementLoaded;
-            //    return;
-            //}
-
-            //var fcElement = this.TargetElement as FrameworkContentElement;
-            //if (fcElement != null)
-            //{
-            //    fcElement.Loaded += this.ElementLoaded;
-            //    return;
-            //}
 
             //if the element is a dependency object, and not a FrameworkElement, nothing is holding onto the reference after the DelayedRegionCreationBehavior
             //is instantiated inside RegionManager.CreateRegion(VisualElement element). If the GC runs before RegionManager.UpdateRegions is called, the region will
@@ -170,24 +150,11 @@ private void UnWireTargetElement()
         {
             TargetElement.PropertyChanged -= TargetElement_ParentChanged;
             Untrack();
-            //var element = TargetElement;
-            //if (element != null)
-            //{
-            //    element.Loaded -= this.ElementLoaded;
-            //    return;
-            //}
-
-            //var fcElement = this.TargetElement as FrameworkContentElement;
-            //if (fcElement != null)
-            //{
-            //    fcElement.Loaded -= this.ElementLoaded;
-            //    return;
-            //}
         }
 
         private void TargetElement_ParentChanged(object sender, PropertyChangedEventArgs e)
         {
-            if(e.PropertyName == nameof(VisualElement.Parent))
+            if(e.PropertyName == nameof(VisualElement.Parent) && TargetElement?.Parent != null)
             {
                 UnWireTargetElement();
                 TryCreateRegion();