Throw if the user tries to show a Window using s:View.Model

Fixes #5

Stylet/ViewManager.cs

@@ -105,6 +105,13 @@ namespace Stylet
             {
                 logger.Info("View.Model changed for {0} from {1} to {2}", targetLocation, oldValue, newValue);
                 var view = this.CreateAndBindViewForModelIfNecessary(newValue);
+                if (view is Window)
+                {
+                    var e = new StyletInvalidViewTypeException(String.Format("s:View.Model=\"...\" tried to show a View of type '{0}', but that View derives from the Window class. " +
+                    "Make sure any Views you display using s:View.Model=\"...\" do not derive from Window (use UserControl or similar)", view.GetType().Name));
+                    logger.Error(e);
+                    throw e;
+                }
                 View.SetContentProperty(targetLocation, view);
             }
             else
@@ -273,4 +280,19 @@ namespace Stylet
             this.ViewTypeName = viewTypeName;
         }
     }
+
+    /// <summary>
+    /// Exception raise when the located View is of the wrong type (Window when expected UserControl, etc)
+    /// </summary>
+    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2237:MarkISerializableTypesWithSerializable")]
+    public class StyletInvalidViewTypeException : Exception
+    {
+        /// <summary>
+        /// Initialises a new instance of the <see cref="StyletInvalidViewException"/> class
+        /// </summary>
+        /// <param name="message">Message associated with the Exception</param>
+        public StyletInvalidViewTypeException(string message)
+            : base(message)
+        { }
+    }
 }

Stylet/WindowManager.cs

@@ -124,8 +124,9 @@ namespace Stylet
             var window = view as Window;
             if (window == null)
             {
-                var e = new ArgumentException(String.Format("WindowManager.ShowWindow or .ShowDialog tried to show a View of type '{0}', but that View doesn't derive from the Window class. " +
-                    "Make sure any Views you display derive from Window (not UserControl, etc)", view == null ? "(null)" : view.GetType().Name));
+                var e = new StyletInvalidViewTypeException(String.Format("WindowManager.ShowWindow or .ShowDialog tried to show a View of type '{0}', but that View doesn't derive from the Window class. " +
+                    "Make sure any Views you display using WindowManager.ShowWindow or .ShowDialog derive from Window (not UserControl, etc)",
+                    view == null ? "(null)" : view.GetType().Name));
                 logger.Error(e);
                 throw e;
             }

StyletUnitTests/ViewManagerTests.cs

@@ -178,6 +178,19 @@ namespace StyletUnitTests
             Assert.AreEqual(view, target.Content);
         }
 
+        [Test]
+        public void OnModelChangedThrowsIfViewIsAWindow()
+        {
+            var target = new ContentControl();
+            var model = new object();
+            var view = new Window();
+            var viewManager = new CreatingAndBindingViewManager(this.viewManagerConfig.Object);
+
+            viewManager.View = view;
+
+            Assert.Throws<StyletInvalidViewTypeException>(() => viewManager.OnModelChanged(target, null, model));
+        }
+
         [Test]
         public void CreateViewForModelReturnsNullIfViewNotFound()
         {

StyletUnitTests/WindowManagerTests.cs

@@ -88,7 +88,7 @@ namespace StyletUnitTests
         {
             var model = new object();
             this.viewManager.Setup(x => x.CreateAndBindViewForModelIfNecessary(model)).Returns(new UIElement());
-            Assert.Throws<ArgumentException>(() => this.windowManager.CreateWindow(model, false));
+            Assert.Throws<StyletInvalidViewTypeException>(() => this.windowManager.CreateWindow(model, false));
         }
 
         [Test]