dotnet/maui · error · BuildException

XC0000

XC0000

Error message

Cannot resolve type "{0}".

What it means

Raised when a type referenced in XAML cannot be resolved to any CLR type after consulting all XmlnsDefinitionAttribute mappings. TryGetTypeReference returns false (no matching type) and GetTypeReference throws BuildException(TypeResolution) with the unresolved 'namespace:name' string.

Source

Thrown at src/Controls/src/Build.Tasks/XmlTypeExtensions.cs:143

			if (types.Distinct(TypeRefComparer.Default).Skip(1).Any())
			{
				typeReference = null;
				return false;
			}

			var type = types.Distinct(TypeRefComparer.Default).FirstOrDefault();
			if (type != null && typeArguments != null && type.HasGenericParameters)
				type = module.ImportReference(type).MakeGenericInstanceType(typeArguments.Select(x => x.GetTypeReference(cache, module, xmlInfo)).ToArray());

			return (typeReference = (type == null) ? null : module.ImportReference(type)) != null;
		}

		public static TypeReference GetTypeReference(this XmlType xmlType, XamlCache cache, ModuleDefinition module, IXmlLineInfo xmlInfo, bool expandToExtension = true)
		{
			if (TryGetTypeReference(xmlType, cache, module, xmlInfo, expandToExtension: expandToExtension, out TypeReference typeReference))
				return typeReference;

			throw new BuildException(BuildExceptionCode.TypeResolution, xmlInfo, null, $"{xmlType.NamespaceUri}:{xmlType.Name}");
		}

		static XmlnsDefinitionAttribute GetXmlnsDefinition(this CustomAttribute ca, AssemblyDefinition asmDef)
		{
			var attr = new XmlnsDefinitionAttribute(
							ca.ConstructorArguments[0].Value as string,
							ca.ConstructorArguments[1].Value as string);

			string assemblyName = null;
			if (ca.Properties.Count > 0)
				assemblyName = ca.Properties[0].Argument.Value as string;
			attr.AssemblyName = assemblyName ?? asmDef.Name.FullName;
			return attr;
		}

		public static IList<XmlnsPrefixAttribute> GetXmlnsPrefixAttributes(ModuleDefinition module)
		{
			var xmlnsPrefixes = new List<XmlnsPrefixAttribute>();

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Add or fix the xmlns declaration, e.g. xmlns:local='clr-namespace:MyApp.Views;assembly=MyApp'.
2. Confirm the assembly containing the type is referenced by the project and that its name/namespace match the clr-namespace string exactly (case-sensitive).
3. If using a custom xmlns uri, ensure the providing assembly has the matching XmlnsDefinitionAttribute and is included in the build.

Example fix

<!-- before -->
<local:MyView xmlns:local="clr-namespace:WrongNamespace;assembly=MyApp" />
<!-- after -->
<local:MyView xmlns:local="clr-namespace:MyApp.Views;assembly=MyApp" />

// At design time, confirm the clr-namespace and assembly referenced in xmlns exist.
// Example: xmlns:local="clr-namespace:MyApp.Views;assembly=MyApp"
// -> assert typeof(MyApp.Views.SomeType).Assembly.GetName().Name == "MyApp".

When it happens

Trigger: TryGetTypeReference finds zero candidate types for the XmlType (types.Distinct(...).FirstOrDefault() is null), so the public GetTypeReference throws BuildException(BuildExceptionCode.TypeResolution, ...) with '{NamespaceUri}:{Name}'.

Common situations: Missing xmlns declaration for a custom control; a clr-namespace that points at the wrong namespace or assembly; the referenced assembly is not referenced by the project or was renamed; case mismatch in namespace or type name.

Related errors

• XC0000
• XC0040
• XC0000
• XC0003
• XC0000

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/b086f7d9cc2aeb48. Report an issue: GitHub.