unoplatform/uno · error · InvalidOperationException

The type '{fullyQualifiedMetadataName}' is not found.

Error message

The type '{fullyQualifiedMetadataName}' is not found.

What it means

GetRequiredTypeByMetadataName resolves a fully-qualified type (RoutedEventArgs, BringIntoViewRequestedEventArgs, etc.) via compilation.GetTypeByMetadataName and throws InvalidOperationException if it returns null. A null return means the type is absent from the compilation — its declaring assembly is not referenced, or the metadata name constant is wrong.

Source

Thrown at src/SourceGenerators/Uno.UI.SourceGenerators/ImplementedRoutedEvents/ImplementedRoutedEventsGenerator.cs:118

			_events.Add("OnPreviewKeyUp", keyRoutedEventArgs);
			_events.Add("OnKeyDown", keyRoutedEventArgs);
			_events.Add("OnKeyUp", keyRoutedEventArgs);

			var characterReceivedRoutedEventArgs = GetRequiredTypeByMetadataName(XamlConstants.Types.CharacterReceivedRoutedEventArgs);
			_events.Add("OnCharacterReceived", characterReceivedRoutedEventArgs);

			var routedEventArgs = GetRequiredTypeByMetadataName(XamlConstants.Types.RoutedEventArgs);
			_events.Add("OnLostFocus", routedEventArgs);
			_events.Add("OnGotFocus", routedEventArgs);

			var bringIntoViewRequestedEventArgs = GetRequiredTypeByMetadataName(XamlConstants.Types.BringIntoViewRequestedEventArgs);
			_events.Add("OnBringIntoViewRequested", bringIntoViewRequestedEventArgs);
		}

		private INamedTypeSymbol GetRequiredTypeByMetadataName(string fullyQualifiedMetadataName)
		{
			var type = _context.Compilation.GetTypeByMetadataName(fullyQualifiedMetadataName);
			return type ?? throw new InvalidOperationException($"The type '{fullyQualifiedMetadataName}' is not found.");
		}

		public override void VisitModule(IModuleSymbol symbol) => VisitNamespace(symbol.GlobalNamespace);

		public override void VisitNamedType(INamedTypeSymbol symbol)
		{
			foreach (var type in symbol.GetTypeMembers())
			{
				VisitNamedType(type);
			}

			ProcessType(symbol);
		}

		public override void VisitNamespace(INamespaceSymbol symbol)
		{
			foreach (var n in symbol.GetNamespaceMembers())
			{

View on GitHub (pinned to 0418340488)

Solutions

1. Add/restore the PackageReference or ProjectReference that provides the missing type (e.g. Microsoft.UI.Xaml / the Uno Microsoft.UI package).
2. Check the reported metadata name against the current Uno/WinUI version in case it was renamed.
3. Run dotnet restore and rebuild to re-resolve references.

Example fix

<!-- before: Microsoft.UI.Xaml not referenced -->
<!-- after -->
<ItemGroup>
  <PackageReference Include="Microsoft.UI.Xaml" Version="..." />
</ItemGroup>

// Before building, confirm the routed-event-arg types resolve in the compilation
var names = new[] { "Microsoft.UI.Xaml.RoutedEventArgs", "Microsoft.UI.Xaml.BringIntoViewRequestedEventArgs" };
foreach (var n in names)
    if (Type.GetType(n) == null) Console.WriteLine($"WARN: {n} not found; add the Microsoft.UI.Xaml reference.");

When it happens

Trigger: The generator requests a routed-event-arg type that is not present in the compilation, e.g. Microsoft.UI.Xaml.RoutedEventArgs when the Microsoft.UI.Xaml reference is missing.

Common situations: Building a project that lacks the Microsoft.UI.Xaml reference; after a namespace/type rename in a dependency; mismatched Uno SDK version where the type moved.

Related errors

• Unable to resolve {symbol} (Reason: {errorTypeSymbol.Candida
• No valid setter found for attached property {name}
• Unable to find type {fullName}
• Expected event to start with 'On'
• The type {0} could not be found

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/8a7e3d635ad2abc7. Report an issue: GitHub.