dotnet/maui · error · BuildException

XC0000

XC0000

Error message

Cannot resolve type "{0}".

What it means

XC0000 TypeResolution thrown by the DataTemplateExtension compiled markup extension when the type named in the TypeName property cannot be resolved to a .NET type. After extracting the type-name string from the ValueNode, the extension calls XmlTypeExtensions.GetTypeReference. If this returns null (type not found in any referenced assembly or declared XML namespace), the build fails.

Solutions

1. Verify the type name is spelled correctly and matches the actual class name.
2. Ensure the XML namespace prefix (e.g. 'local:') is declared at the root element and maps to the correct CLR namespace and assembly.
3. Confirm the assembly containing the type is referenced by the project.
4. If the type was renamed/moved, update the TypeName value to match the new fully-qualified name.

Example fix

<!-- before (typo: MyItemVeiw) -->
<ContentPage xmlns:local="clr-namespace:MyApp.Views">
  <DataTemplate TypeName="local:MyItemVeiw" />
</ContentPage>

<!-- after -->
<ContentPage xmlns:local="clr-namespace:MyApp.Views">
  <DataTemplate TypeName="local:MyItemView" />
</ContentPage>

// Validate that a type name referenced in DataTemplate TypeName resolves
static bool CanResolveType(string typeName, Assembly[] searchAssemblies)
    => searchAssemblies.SelectMany(a => a.GetTypes())
           .Any(t => t.Name == typeName || t.FullName == typeName);

When it happens

Trigger: Specifying a TypeName value that does not resolve: a misspelled type name, a type in an undeclared XML namespace prefix, or a type that exists in an assembly not referenced by the project. Example: TypeName='local:MyItemVeiw' (typo), TypeName='NonExistentType'.

Common situations: Typo in the type name. Missing or wrong xmlns:local declaration. The type was renamed or moved to a different namespace. The assembly containing the type is not added as a project reference. Using a type name without a namespace prefix when it is not in the default namespace.

Related errors

• XC0003
• XC0003
• XC0040
• XC0000
• XC0004

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/e62b19be44c44eac. Report an issue: GitHub.

Appendix: source

Thrown at src/Controls/src/Build.Tasks/CompiledMarkupExtensions/DataTemplateExtension.cs:26

using static Mono.Cecil.Cil.OpCodes;

namespace Microsoft.Maui.Controls.Build.Tasks
{
	class DataTemplateExtension : ICompiledMarkupExtension
	{
		public IEnumerable<Instruction> ProvideValue(ElementNode node, ModuleDefinition module, ILContext context, out TypeReference typeRef)
		{
			typeRef = module.ImportReference(context.Cache, ("Microsoft.Maui.Controls", "Microsoft.Maui.Controls", "DataTemplate"));
			var name = new XmlName("", "TypeName");

			if (!node.Properties.TryGetValue(name, out INode typeNameNode) && node.CollectionItems.Any())
				typeNameNode = node.CollectionItems[0];

			if (typeNameNode is not ValueNode valueNode)
				throw new BuildException(BuildExceptionCode.PropertyMissing, node as IXmlLineInfo, null, "TypeName", typeof(Microsoft.Maui.Controls.Xaml.DataTemplateExtension));

			var contentTypeRef = module.ImportReference(XmlTypeExtensions.GetTypeReference(context.Cache, valueNode.Value as string, module, node as BaseNode))
				?? throw new BuildException(BuildExceptionCode.TypeResolution, node as IXmlLineInfo, null, valueNode.Value);

			var dataTemplateCtor = module.ImportCtorReference(context.Cache, typeRef, new[] { module.ImportReference(context.Cache, ("mscorlib", "System", "Type")) });
			return [
				Create(Ldtoken, module.ImportReference(contentTypeRef)),
				Create(Call, module.ImportMethodReference(context.Cache, ("mscorlib", "System", "Type"), methodName: "GetTypeFromHandle", parameterTypes: new[] { ("mscorlib", "System", "RuntimeTypeHandle") }, isStatic: true)),
				Create(Newobj, dataTemplateCtor),
			];
		}
	}
}

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