Fixed so its possible to use MultiBinding and PriorityBinding on a DesignItemProperty and that it writes as expected to XAML.

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Tests/Designer/ModelTestHelper.cs

@@ -21,6 +21,8 @@ namespace ICSharpCode.WpfDesign.Tests.Designer
 	/// </summary>
 	public class ModelTestHelper
 	{
+		public const string DesignerTestsNamespace = "clr-namespace:ICSharpCode.WpfDesign.Tests.Designer;assembly=ICSharpCode.WpfDesign.Tests";
+		
 		protected StringBuilder log;
 		
 		protected XamlDesignContext CreateContext(string xaml)
@@ -40,7 +42,8 @@ namespace ICSharpCode.WpfDesign.Tests.Designer
 		{
 			XamlDesignContext context = CreateContext(@"<Canvas
   xmlns=""http://schemas.microsoft.com/winfx/2006/xaml/presentation""
-  xmlns:x=""http://schemas.microsoft.com/winfx/2006/xaml"">
+  xmlns:x=""http://schemas.microsoft.com/winfx/2006/xaml""
+  xmlns:t=""" + DesignerTestsNamespace + @""">
   " + xaml + "</Canvas>");
 			Canvas canvas = (Canvas)context.RootItem.Component;
 			DesignItem canvasChild = context.Services.Component.GetDesignItem(canvas.Children[0]);
@@ -54,7 +57,8 @@ namespace ICSharpCode.WpfDesign.Tests.Designer
 			expectedXaml =
 				"<?xml version=\"1.0\" encoding=\"utf-16\"?>\n" +
 				("<Canvas xmlns=\"http://schemas.microsoft.com/winfx/2006/xaml/presentation\" " +
-				 "xmlns:x=\"http://schemas.microsoft.com/winfx/2006/xaml\">\n" + expectedXaml.Trim())
+				 "xmlns:x=\"http://schemas.microsoft.com/winfx/2006/xaml\" " +
+				 "xmlns:t=\"" + DesignerTestsNamespace + "\">\n" + expectedXaml.Trim())
 				.Replace("\r", "").Replace("\n", "\n  ")
 				+ "\n</Canvas>";
 			

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Tests/Designer/ModelTests.cs

@@ -1,17 +1,18 @@
 // Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
 // This code is distributed under the GNU LGPL (for details please see \doc\license.txt)
 
-using System;
-using System.Text;
-using System.IO;
-using System.Xml;
-using System.Diagnostics;
-using System.Windows;
-using System.Windows.Controls;
-using NUnit.Framework;
-using ICSharpCode.WpfDesign.Designer;
-using ICSharpCode.WpfDesign.Designer.Xaml;
-using ICSharpCode.WpfDesign.Designer.Services;
+using System;
+using System.Text;
+using System.IO;
+using System.Xml;
+using System.Diagnostics;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using NUnit.Framework;
+using ICSharpCode.WpfDesign.Designer;
+using ICSharpCode.WpfDesign.Designer.Xaml;
+using ICSharpCode.WpfDesign.Designer.Services;
 
 namespace ICSharpCode.WpfDesign.Tests.Designer
 {
@@ -235,5 +236,52 @@ namespace ICSharpCode.WpfDesign.Tests.Designer
 			                           "</Canvas>", canvas.Context);
 			AssertLog("");
 		}
+		
+		[Test]
+		public void AddMultiBindingToTextBox()
+		{
+			DesignItem button = CreateCanvasContext("<Button/>");
+			DesignItem canvas = button.Parent;
+			DesignItem textBox = canvas.Services.Component.RegisterComponentForDesigner(new TextBox());
+			canvas.Properties["Children"].CollectionElements.Add(textBox);
+			
+			textBox.Properties[TextBox.TextProperty].SetValue(new MultiBinding());
+			DesignItem multiBindingItem = textBox.Properties[TextBox.TextProperty].Value;
+			multiBindingItem.Properties["Converter"].SetValue(new MyMultiConverter());
+
+			DesignItemProperty bindingsProp = multiBindingItem.ContentProperty;
+			Assert.IsTrue(bindingsProp.IsCollection);
+			Assert.AreEqual(bindingsProp.Name, "Bindings");
+			
+			DesignItem bindingItem = canvas.Services.Component.RegisterComponentForDesigner(new Binding());
+			bindingItem.Properties["Path"].SetValue("SomeProperty");
+			bindingsProp.CollectionElements.Add(bindingItem);
+			
+			string expectedXaml = "<Button />\n" +
+			                      "<TextBox>\n" +
+			                      "  <MultiBinding>\n" +
+			                      "    <MultiBinding.Converter>\n" +
+			                      "      <t:MyMultiConverter />\n" +
+			                      "    </MultiBinding.Converter>\n" +
+			                      "    <Binding Path=\"SomeProperty\" />\n" +
+			                      "  </MultiBinding>\n" +
+			                      "</TextBox>";
+			
+			AssertCanvasDesignerOutput(expectedXaml, button.Context);
+			AssertLog("");
+		}
+	}
+	
+	public class MyMultiConverter : IMultiValueConverter
+	{
+		public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
+		{
+			return null;
+		}
+		
+		public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
+		{
+			return new object[targetTypes.Length];
+		}
 	}
 }

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.XamlDom/Project/MarkupExtensionPrinter.cs

@@ -18,6 +18,11 @@ namespace ICSharpCode.WpfDesign.XamlDom
 		/// </summary>
 		public static bool CanPrint(XamlObject obj)
 		{
+			if (obj.ElementType == typeof(System.Windows.Data.MultiBinding) ||
+				obj.ElementType == typeof(System.Windows.Data.PriorityBinding)) {
+				return false;
+			}
+
 			return true;
 		}
 		

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.XamlDom/Project/XamlObject.cs

@@ -175,7 +175,7 @@ namespace ICSharpCode.WpfDesign.XamlDom
 		void UpdateMarkupExtensionChain()
 		{
 			var obj = this;
-			while (obj != null && obj.IsMarkupExtension) {
+			while (obj != null && obj.IsMarkupExtension && obj.ParentProperty != null) {
 				obj.ParentProperty.UpdateValueOnInstance();
 				obj = obj.ParentObject;
 			}			
@@ -345,7 +345,7 @@ namespace ICSharpCode.WpfDesign.XamlDom
 
 		void CreateWrapper()
 		{
-			if (Instance is Binding) {
+			if (Instance is BindingBase) {
 				wrapper = new BindingWrapper();
 			} else if (Instance is StaticResourceExtension) {
 				wrapper = new StaticResourceWrapper();