Refactor to add {s:ViewModel}, and use that for actions

Stylet/Stylet.csproj

@@ -131,6 +131,7 @@
     <Compile Include="Xaml\View.cs" />
     <Compile Include="ViewManager.cs" />
     <Compile Include="WindowManager.cs" />
+    <Compile Include="Xaml\ViewModelExtension.cs" />
   </ItemGroup>
   <ItemGroup>
     <Page Include="MessageBoxView.xaml">

Stylet/ViewManager.cs

@@ -245,8 +245,9 @@ namespace Stylet
             var viewAsFrameworkElement = view as FrameworkElement;
             if (viewAsFrameworkElement != null)
             {
-                logger.Info("Setting {0}'s DataContext to {1}", view, viewModel);
+                logger.Info("Setting {0}'s DataContext and ViewModel proxy to {1}", view, viewModel);
                 viewAsFrameworkElement.DataContext = viewModel;
+                View.SetViewModel(viewAsFrameworkElement, viewModel);
             }
 
             var viewModelAsViewAware = viewModel as IViewAware;

Stylet/Xaml/ActionBase.cs

@@ -78,13 +78,7 @@ namespace Stylet.Xaml
                 Mode = BindingMode.OneWay,
                 Source = this.Subject,
             });
-            multiBinding.Bindings.Add(new Binding()
-            {
-                Path = new PropertyPath(View.BackupActionTargetBindingProxyProperty),
-                Mode = BindingMode.OneWay,
-                Source = this.Subject,
-                Converter = new BindingProxyToValueConverter(),
-            });
+            multiBinding.Bindings.Add(View.GetBindingToViewModel(this.Subject));
 
             //var binding = new Binding()
             //{

Stylet/Xaml/ActionExtension.cs

@@ -107,11 +107,6 @@ namespace Stylet.Xaml
             if (targetObjectAsDependencyObject == null)
                 return this;
 
-            // In some cases, the View.ActionTarget attached property won't be propagated - think popups, context menus, KeyBindings, etc
-            // In this case, we can grab a reference to the last-set View.ActionTarget using the dynamic resources mechanism
-            var resourceReference = new DynamicResourceExtension(View.ActionTargetProxyResourceKey).ProvideValue(serviceProvider);
-            targetObjectAsDependencyObject.SetValue(View.BackupActionTargetBindingProxyProperty, resourceReference);
-
             var propertyAsDependencyProperty = valueService.TargetProperty as DependencyProperty;
             if (propertyAsDependencyProperty != null && propertyAsDependencyProperty.PropertyType == typeof(ICommand))
             {

Stylet/Xaml/BindingProxy.cs

@@ -28,6 +28,8 @@ namespace Stylet.Xaml
 
     internal class BindingProxyToValueConverter : IValueConverter
     {
+        public static readonly BindingProxyToValueConverter Instance = new BindingProxyToValueConverter();
+
         public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
         {
             var proxy = value as BindingProxy;

Stylet/Xaml/View.cs

@@ -17,7 +17,7 @@ namespace Stylet.Xaml
 
         internal const string ViewManagerResourceKey = "b9a38199-8cb3-4103-8526-c6cfcd089df7";
 
-        internal const string ActionTargetProxyResourceKey = "8b7cb732-8a14-4813-a580-b1f3cccea7b7";
+        internal const string ViewModelProxyResourceKey = "8b7cb732-8a14-4813-a580-b1f3cccea7b7";
 
         /// <summary>
         /// Initial value of the ActionTarget property.
@@ -49,28 +49,7 @@ namespace Stylet.Xaml
         /// The object's ActionTarget. This is used to determine what object to call Actions on by the ActionExtension markup extension.
         /// </summary>
         public static readonly DependencyProperty ActionTargetProperty =
-            DependencyProperty.RegisterAttached("ActionTarget", typeof(object), typeof(View), new FrameworkPropertyMetadata(InitialActionTarget, FrameworkPropertyMetadataOptions.Inherits, (d, e) =>
-            {
-                // Also set a binding proxy if we can, in case there's something weird in the way
-                var frameworkElement = d as FrameworkElement;
-                if (frameworkElement == null)
-                    return;
-
-                // Don't set if it's been set already
-                var currentValue = (BindingProxy)d.GetValue(BackupActionTargetBindingProxyProperty);
-                if (currentValue != null && currentValue.Data == e.NewValue)
-                    return;
-                
-                var bindingProxy = new BindingProxy()
-                {
-                    Data = e.NewValue,
-                };
-                frameworkElement.Resources[ActionTargetProxyResourceKey] = bindingProxy;
-            }));
-
-        internal static readonly DependencyProperty BackupActionTargetBindingProxyProperty =
-            DependencyProperty.RegisterAttached("BackupActionTargetBindingProxy", typeof(BindingProxy), typeof(View), new PropertyMetadata(null));
-
+            DependencyProperty.RegisterAttached("ActionTarget", typeof(object), typeof(View), new FrameworkPropertyMetadata(InitialActionTarget));
 
         /// <summary>
         /// Fetch the ViewModel currently associated with a given object
@@ -129,6 +108,47 @@ namespace Stylet.Xaml
                 }
             }));
 
+        /// <summary>
+        /// Set the ViewModel which can be subsequently retrieved using {s:ViewModel}
+        /// </summary>
+        /// <param name="view">View to store the ViewModel for</param>
+        /// <param name="viewModel">ViewModel to store</param>
+        public static void SetViewModel(FrameworkElement view, object viewModel)
+        {
+            var bindingProxy = new BindingProxy()
+            {
+                Data = viewModel,
+            };
+            view.Resources[ViewModelProxyResourceKey] = bindingProxy;
+        }
+
+        /// <summary>
+        /// Fetch a binding which can be used to retrieve the ViewModel associated with a View
+        /// </summary>
+        /// <param name="view">View to fetch the ViewModel for</param>
+        /// <returns>Binding which can retrieve the ViewModel</returns>
+        public static Binding GetBindingToViewModel(DependencyObject view)
+        {
+            if (view.GetValue(ViewModelProxyProperty) == null)
+            {
+                var resource = new DynamicResourceExtension(ViewModelProxyResourceKey).ProvideValue(null);
+                view.SetValue(ViewModelProxyProperty, resource);
+            }
+
+            var binding = new Binding()
+            {
+                Source = view,
+                Path = new PropertyPath(View.ViewModelProxyProperty),
+                Mode = BindingMode.OneWay,
+                Converter = BindingProxyToValueConverter.Instance,
+            };
+
+            return binding;
+        }
+
+        internal static readonly DependencyProperty ViewModelProxyProperty =
+            DependencyProperty.RegisterAttached("ViewModelProxy", typeof(BindingProxy), typeof(View), new PropertyMetadata(null));
+
         /// <summary>
         /// Helper to set the Content property of a given object to a particular View
         /// </summary>

Stylet/Xaml/ViewModelExtension.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows;
+using System.Windows.Data;
+using System.Windows.Markup;
+
+namespace Stylet.Xaml
+{
+    /// <summary>
+    /// MarkupExtension which can retrieve the ViewModel for the current View, if available
+    /// </summary>
+    public class ViewModelExtension : MarkupExtension
+    {
+        /// <summary>
+        /// Instantiates a new instsance of the <see cref="ViewModelExtension"/> class
+        /// </summary>
+        public ViewModelExtension()
+        {
+        }
+
+        /// <summary>
+        ///  When implemented in a derived class, returns an object that is provided as the
+        ///  value of the target property for this markup extension.
+        /// </summary>
+        /// <param name="serviceProvider">A service provider helper that can provide services for the markup extension.</param>
+        /// <returns>The object value to set on the property where the extension is applied.</returns>
+        public override object ProvideValue(IServiceProvider serviceProvider)
+        {
+            var valueService = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget));
+            var targetObjectAsDependencyObject = valueService.TargetObject as DependencyObject;
+            if (targetObjectAsDependencyObject == null)
+                return this;
+
+            return View.GetBindingToViewModel(targetObjectAsDependencyObject).ProvideValue(serviceProvider);
+        }
+    }
+}

StyletIntegrationTests/ShellView.xaml

@@ -41,7 +41,7 @@
                     </TextBox.InputBindings>
                     <TextBox.ContextMenu>
                         <ContextMenu>
-                            <MenuItem Header="Click Here" Command="{s:Action ShowActionTargetSaved}"/>
+                            <MenuItem Header="{Binding Foo}" DataContext="{s:ViewModel}" Command="{s:Action ShowActionTargetSaved}"/>
                         </ContextMenu>
                     </TextBox.ContextMenu>
                 </TextBox>

StyletIntegrationTests/ShellViewModel.cs

@@ -12,6 +12,8 @@ namespace StyletIntegrationTests
     {
         private IWindowManager windowManager;
 
+        public string Foo => "Foo";
+
         public ShellViewModel(IWindowManager windowManager)
         {
             this.windowManager = windowManager;