fix TreeNode implementation

src/Main/Base/Project/Dom/ClassBrowser/WorkspaceTreeNode.cs

@@ -24,6 +24,11 @@ namespace ICSharpCode.SharpDevelop.Dom.ClassBrowser
 			this.workspace = workspace;
 		}
 		
+		protected override object GetModel()
+		{
+			return workspace;
+		}
+		
 		protected override IModelCollection<object> ModelChildren {
 			get { return workspace.LoadedAssemblies; }
 		}
@@ -62,6 +67,11 @@ namespace ICSharpCode.SharpDevelop.Dom.ClassBrowser
 			this.solution = solution;
 		}
 		
+		protected override object GetModel()
+		{
+			return solution;
+		}
+		
 		public override object Text {
 			get { return "Solution " + solution.Name; }
 		}
@@ -90,6 +100,11 @@ namespace ICSharpCode.SharpDevelop.Dom.ClassBrowser
 			this.project = project;
 		}
 		
+		protected override object GetModel()
+		{
+			return project;
+		}
+		
 		public override object Text {
 			get { return project.Name; }
 		}
@@ -118,6 +133,11 @@ namespace ICSharpCode.SharpDevelop.Dom.ClassBrowser
 			this.model = model;
 		}
 		
+		protected override object GetModel()
+		{
+			return model;
+		}
+		
 		protected override IComparer<SharpTreeNode> NodeComparer {
 			get { return NodeTextComparer; }
 		}
@@ -138,6 +158,11 @@ namespace ICSharpCode.SharpDevelop.Dom.ClassBrowser
 			this.model = model;
 		}
 		
+		protected override object GetModel()
+		{
+			return model;
+		}
+		
 		protected override IComparer<SharpTreeNode> NodeComparer {
 			get { return NodeTextComparer; }
 		}
@@ -166,6 +191,11 @@ namespace ICSharpCode.SharpDevelop.Dom.ClassBrowser
 			this.definition = definition;
 		}
 		
+		protected override object GetModel()
+		{
+			return definition;
+		}
+		
 		public override object Icon {
 			// TODO why do I have to resolve this?
 			get { return ClassBrowserIconService.GetIcon(definition.Resolve()).ImageSource; }

src/Main/Base/Project/Dom/KeyedModelCollection.cs

@@ -32,6 +32,13 @@ namespace ICSharpCode.SharpDevelop.Dom
 			dict.Remove(getKeyForValue(item));
 		}
 		
+		protected override void ValidateItem(TValue item)
+		{
+			base.ValidateItem(item);
+			if (dict.ContainsKey(getKeyForValue(item)))
+				throw new ArgumentException("An item with the same key has already been added to the collection.");
+		}
+		
 		public TValue this[TKey key] {
 			get { return dict[key]; }
 		}

src/Main/SharpDevelop/Dom/ProjectAssemblyModel.cs

@@ -61,16 +61,6 @@ namespace ICSharpCode.SharpDevelop.Dom
 		void TypeDeclarationsCollectionChanged(IReadOnlyCollection<ITypeDefinitionModel> removedItems, IReadOnlyCollection<ITypeDefinitionModel> addedItems)
 		{
 			NamespaceModel ns;
-			foreach (ITypeDefinitionModel removedItem in removedItems) {
-				if (namespaces.TryGetValue(removedItem.Namespace, out ns)) {
-					ns.Types.Remove(removedItem);
-					while (ns.ParentNamespace != null && ns.Types.Count == 0 && ns.ChildNamespaces.Count == 0) {
-						((NamespaceModel)ns.ParentNamespace).ChildNamespaces.Remove(ns);
-						namespaces.Remove(ns);
-						ns = (NamespaceModel)ns.ParentNamespace;
-					}
-				}
-			}
 			foreach (ITypeDefinitionModel addedItem in addedItems) {
 				if (!namespaces.TryGetValue(addedItem.Namespace, out ns)) {
 					string[] parts = addedItem.Namespace.Split('.');
@@ -84,13 +74,28 @@ namespace ICSharpCode.SharpDevelop.Dom
 						level++;
 					}
 					while (level < parts.Length) {
-						ns = new NamespaceModel(context, ns, parts[level]);
-						namespaces.Add(ns);
+						var child = new NamespaceModel(context, ns, parts[level]);
+						ns.ChildNamespaces.Add(child);
+						ns = child;
 						level++;
 					}
+					if (!namespaces.Contains(ns))
+						namespaces.Add(ns);
 					ns.Types.Add(addedItem);
 				}
 			}
+			foreach (ITypeDefinitionModel removedItem in removedItems) {
+				if (namespaces.TryGetValue(removedItem.Namespace, out ns)) {
+					ns.Types.Remove(removedItem);
+					if (ns.Types.Count == 0)
+						namespaces.Remove(ns);
+					while (ns.ParentNamespace != null) {
+						if (ns.ChildNamespaces.Count == 0 && ns.Types.Count == 0)
+							((NamespaceModel)ns.ParentNamespace).ChildNamespaces.Remove(ns);
+						ns = (NamespaceModel)ns.ParentNamespace;
+					}
+				}
+			}
 		}
 	}
 }