Turn s:ViewModel into a proper binding, making it vaguely useful

Stylet/Stylet.csproj

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

Stylet/Xaml/View.cs

@@ -150,6 +150,15 @@ namespace Stylet.Xaml
             view.Resources[ViewModelProxyResourceKey] = bindingProxy;
         }
 
+        internal static void EnsureViewModelProxyValueSetUp(DependencyObject view)
+        {
+            if (view.GetValue(ViewModelProxyProperty) == null)
+            {
+                var resource = new DynamicResourceExtension(ViewModelProxyResourceKey).ProvideValue(null);
+                view.SetValue(ViewModelProxyProperty, resource);
+            }
+        }
+
         /// <summary>
         /// Fetch a binding which can be used to retrieve the ViewModel associated with a View
         /// </summary>
@@ -157,11 +166,7 @@ namespace Stylet.Xaml
         /// <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);
-            }
+            EnsureViewModelProxyValueSetUp(view);
 
             var binding = new Binding()
             {
@@ -174,7 +179,7 @@ namespace Stylet.Xaml
             return binding;
         }
 
-        private static readonly DependencyProperty ViewModelProxyProperty =
+        internal static readonly DependencyProperty ViewModelProxyProperty =
             DependencyProperty.RegisterAttached("ViewModelProxy", typeof(BindingProxy), typeof(View), new PropertyMetadata(null));
 
         /// <summary>

Stylet/Xaml/ViewModelBindingExtension.cs

@@ -0,0 +1,96 @@
+using System;
+using System.Globalization;
+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 ViewModelBindingExtension : MarkupExtension
+    {
+        /// <summary>
+        /// Gets or sets the path to the property
+        /// </summary>
+        public string Path { get; set; }
+
+        /// <summary>
+        /// Gets or sets the converter to use.
+        /// </summary>
+        public IValueConverter Converter { get; set; }
+
+        /// <summary>
+        /// Gets or sets the culture in which to evaluate the converter.
+        /// </summary>
+        public CultureInfo ConverterCulture { get; set; }
+
+        /// <summary>
+        /// Gets or sets the parameter to pass to the Converter.
+        /// </summary>
+        public object ConverterParameter { get; set; }
+
+        /// <summary>
+        /// Gets or sets the value to use when the binding is unable to return a value
+        /// </summary>
+        public object FallbackValue { get; set; }
+
+        /// <summary>
+        /// Gets or sets a string that specifies how to format the binding if it displays the bound value as a string
+        /// </summary>
+        public string StringFormat { get; set; }
+
+        /// <summary>
+        /// Gets or sets the value that is used in the target when the value of the source is null
+        /// </summary>
+        public object TargetNullValue { get; set; }
+
+        /// <summary>
+        /// Instantiates a new instance of the <see cref="ViewModelBindingExtension"/> class
+        /// </summary>
+        public ViewModelBindingExtension()
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the Binding class with an initial path
+        /// </summary>
+        /// <param name="path">The initial Path for the binding</param>
+        public ViewModelBindingExtension(string path)
+        {
+            this.Path = path;
+        }
+
+        /// <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;
+
+            View.EnsureViewModelProxyValueSetUp(targetObjectAsDependencyObject);
+
+            var binding = new Binding()
+            {
+                Source = targetObjectAsDependencyObject,
+                Path = new PropertyPath("(0).(1)." + this.Path, View.ViewModelProxyProperty, BindingProxy.DataProperty),
+                Mode = BindingMode.OneWay,
+                Converter = this.Converter,
+                ConverterCulture = this.ConverterCulture,
+                ConverterParameter = this.ConverterParameter,
+                FallbackValue = this.FallbackValue,
+                StringFormat = this.StringFormat,
+                TargetNullValue = this.TargetNullValue,
+            };
+
+            return binding.ProvideValue(serviceProvider);
+        }
+    }
+}

Stylet/Xaml/ViewModelExtension.cs

@@ -1,35 +0,0 @@
-using System;
-using System.Windows;
-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 instance 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

@@ -51,7 +51,7 @@
         <GroupBox DockPanel.Dock="Top" Header="{}{ViewModel}" Padding="10">
             <DockPanel DataContext="{x:Null}">
                 <TextBlock DockPanel.Dock="Top">Ensure that the label below displays the text "Pass":</TextBlock>
-                <TextBlock DockPanel.Dock="Top" DataContext="{s:ViewModel}" Text="{Binding ViewModelTestLabel}"/>
+                <TextBlock DockPanel.Dock="Top" Text="{s:ViewModelBinding ViewModelTestLabel}"/>
             </DockPanel>
         </GroupBox>
     </DockPanel>