XML-namespaces for controls outside the default XML-namespace is now declared in the document root.

As prefix for the XML-namespaces it primarily uses the value from XmlnsPrefixAttribute if it exists for the XML-namespace, otherwise a "ControlsX" name is generated, where X is the first free value.

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

@@ -17,7 +17,9 @@ namespace ICSharpCode.WpfDesign.XamlDom
 		XamlObject _rootElement;
 		IServiceProvider _serviceProvider;
 		
-		XamlTypeFinder _typeFinder;
+		XamlTypeFinder _typeFinder;
+
+        int namespacePrefixCounter;
 		
 		internal XmlDocument XmlDocument {
 			get { return _xmlDoc; }
@@ -164,11 +166,13 @@ namespace ICSharpCode.WpfDesign.XamlDom
 			bool hasStringConverter = c.CanConvertTo(ctx, typeof(string)) && c.CanConvertFrom(typeof(string));
 			if (forProperty != null && hasStringConverter) {
 				return new XamlTextValue(this, c.ConvertToInvariantString(ctx, instance));
-			}
+			}
-			
+
-			
+            string ns = GetNamespaceFor(elementType);
-			XmlElement xml = _xmlDoc.CreateElement(elementType.Name, GetNamespaceFor(elementType));
+            string prefix = GetPrefixForNamespace(ns);
-			
+
+            XmlElement xml = _xmlDoc.CreateElement(prefix, elementType.Name, ns);
+
 			if (hasStringConverter &&
 			    XamlObject.GetContentPropertyName(elementType) != null)
 			{
@@ -181,6 +185,44 @@ namespace ICSharpCode.WpfDesign.XamlDom
 		internal string GetNamespaceFor(Type type)
 		{
 			return _typeFinder.GetXmlNamespaceFor(type.Assembly, type.Namespace);
-		}
+		}
+
+        internal string GetPrefixForNamespace(string @namespace)
+        {
+            if (@namespace == XamlConstants.PresentationNamespace)
+            {
+                return null;
+            }
+
+            string prefix = _xmlDoc.DocumentElement.GetPrefixOfNamespace(@namespace);
+
+            if (String.IsNullOrEmpty(prefix))
+            {
+                prefix = _typeFinder.GetPrefixForXmlNamespace(@namespace);
+
+                string existingNamespaceForPrefix = null;
+                if (!String.IsNullOrEmpty(prefix))
+                {
+                    existingNamespaceForPrefix = _xmlDoc.DocumentElement.GetNamespaceOfPrefix(prefix);
+                }
+
+                if (String.IsNullOrEmpty(prefix) ||
+                    !String.IsNullOrEmpty(existingNamespaceForPrefix) &&
+                    existingNamespaceForPrefix != @namespace)
+                {
+                    do
+                    {
+                        prefix = "Controls" + namespacePrefixCounter++;
+                    } while (!String.IsNullOrEmpty(_xmlDoc.DocumentElement.GetNamespaceOfPrefix(prefix)));
+                }
+
+                string xmlnsPrefix = _xmlDoc.DocumentElement.GetPrefixOfNamespace(XamlConstants.XmlnsNamespace);
+                System.Diagnostics.Debug.Assert(!String.IsNullOrEmpty(xmlnsPrefix));
+
+                _xmlDoc.DocumentElement.SetAttribute(xmlnsPrefix + ":" + prefix, @namespace);
+            }
+
+            return prefix;
+        }
 	}
 }

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

@@ -42,11 +42,13 @@ namespace ICSharpCode.WpfDesign.XamlDom
 		}
 		
 		sealed class XamlNamespace
-		{
+		{
+            internal readonly string XmlNamespacePrefix;
 			internal readonly string XmlNamespace;
 			
-			internal XamlNamespace(string xmlNamespace)
+			internal XamlNamespace(string xmlNamespacePrefix, string xmlNamespace)
-			{
+			{
+                this.XmlNamespacePrefix = xmlNamespacePrefix;
 				this.XmlNamespace = xmlNamespace;
 			}
 			
@@ -54,7 +56,7 @@ namespace ICSharpCode.WpfDesign.XamlDom
 			
 			internal XamlNamespace Clone()
 			{
-				XamlNamespace copy = new XamlNamespace(this.XmlNamespace);
+				XamlNamespace copy = new XamlNamespace(this.XmlNamespacePrefix, this.XmlNamespace);
 				// AssemblyNamespaceMapping is immutable
 				copy.ClrNamespaces.AddRange(this.ClrNamespaces);
 				return copy;
@@ -107,7 +109,25 @@ namespace ICSharpCode.WpfDesign.XamlDom
 			} else {
 				return "clr-namespace:" + mapping.Namespace + ";assembly=" + mapping.Assembly.GetName().Name;
 			}
-		}
+		}
+
+        /// <summary>
+        /// Gets the prefix to use for the specified XML namespace,
+        /// or null if no suitable prefix could be found.
+        /// </summary>
+        public string GetPrefixForXmlNamespace(string xmlNamespace)
+        {
+            XamlNamespace ns;
+
+            if (namespaces.TryGetValue(xmlNamespace, out ns))
+            {
+                return ns.XmlNamespacePrefix;
+            }
+            else
+            {
+                return null;
+            }
+        }
 		
 		XamlNamespace ParseNamespace(string xmlNamespace)
 		{
@@ -127,7 +147,7 @@ namespace ICSharpCode.WpfDesign.XamlDom
 				}
 				assembly = name.Substring("assembly=".Length);
 			}
-			XamlNamespace ns = new XamlNamespace(xmlNamespace);
+			XamlNamespace ns = new XamlNamespace(null, xmlNamespace);
 			Assembly asm = LoadAssembly(assembly);
 			if (asm != null) {
 				AddMappingToNamespace(ns, new AssemblyNamespaceMapping(asm, namespaceName));
@@ -154,11 +174,19 @@ namespace ICSharpCode.WpfDesign.XamlDom
 		public void RegisterAssembly(Assembly assembly)
 		{
 			if (assembly == null)
-				throw new ArgumentNullException("assembly");
+				throw new ArgumentNullException("assembly");
+
+            Dictionary<string, string> namespacePrefixes = new Dictionary<string, string>();
+            foreach (XmlnsPrefixAttribute xmlnsPrefix in assembly.GetCustomAttributes(typeof(XmlnsPrefixAttribute), true)) {
+                namespacePrefixes.Add(xmlnsPrefix.XmlNamespace, xmlnsPrefix.Prefix);
+            }
+
 			foreach (XmlnsDefinitionAttribute xmlnsDef in assembly.GetCustomAttributes(typeof(XmlnsDefinitionAttribute), true)) {
-				XamlNamespace ns;
+				XamlNamespace ns;
-				if (!namespaces.TryGetValue(xmlnsDef.XmlNamespace, out ns)) {
+				if (!namespaces.TryGetValue(xmlnsDef.XmlNamespace, out ns)) {
-					ns = namespaces[xmlnsDef.XmlNamespace] = new XamlNamespace(xmlnsDef.XmlNamespace);
+                    string prefix;
+                    namespacePrefixes.TryGetValue(xmlnsDef.XmlNamespace, out prefix);
+                    ns = namespaces[xmlnsDef.XmlNamespace] = new XamlNamespace(prefix, xmlnsDef.XmlNamespace);
 				}
 				if (string.IsNullOrEmpty(xmlnsDef.AssemblyName)) {
 					AddMappingToNamespace(ns, new AssemblyNamespaceMapping(assembly, xmlnsDef.ClrNamespace));