unoplatform/uno · error · XamlGenerationException

Unable to find 'MethodName' property on '{symbol}'

Error message

Unable to find 'MethodName' property on '{symbol}'

What it means

Thrown by BuildXamlTypeConverterLiteralValue when a type decorated with [CreateFromString] does not have a 'MethodName' named argument on the attribute. The generator reads the MethodName named argument to find the conversion method; if it is absent or null, this XamlGenerationException fires.

Source

Thrown at src/SourceGenerators/Uno.UI.SourceGenerators/XamlGenerator/XamlFileGenerator.cs:2274

		}

		private bool IsCustomMarkupExtensionType(XamlType? xamlType, bool allowExtensionSuffix = true) =>
			// Determine if the type is a custom markup extension
			GetMarkupExtensionType(xamlType, allowExtensionSuffix) != null;

		private bool IsXamlTypeConverter(INamedTypeSymbol? symbol)
		{
			return symbol?.GetAttributes().Any(a => a.AttributeClass?.Equals(Generation.CreateFromStringAttributeSymbol.Value, SymbolEqualityComparer.Default) == true) == true;
		}

		private string BuildXamlTypeConverterLiteralValue(INamedTypeSymbol? symbol, string memberValue, bool includeQuotations, IXamlLocation location)
		{
			var attributeData = symbol.FindAttribute(Generation.CreateFromStringAttributeSymbol.Value);
			var targetMethod = attributeData?.NamedArguments.FirstOrDefault(kvp => kvp.Key == "MethodName").Value.Value?.ToString();

			if (targetMethod == null)
			{
				throw new XamlGenerationException($"Unable to find 'MethodName' property on '{symbol}'", location);
			}

			// Since the MethodName value can simply be the name of the method
			// without its full path, example: nameof(MyConversionMethod), we must
			// make sure to fully qualify the method name with its namespace
			var fullyQualifiedOwnerType = !targetMethod.Contains('.')
				? $"{symbol?.GetFullyQualifiedTypeIncludingGlobal()}.{targetMethod}"
				: GetGlobalizedTypeName(targetMethod);

			var literalValue = default(string);
			if (includeQuotations)
			{
				// Return a string that contains the code which calls the "conversion" function with the member value
				literalValue = "{0}(\"{1}\")".InvariantCultureFormat(fullyQualifiedOwnerType, memberValue);
			}
			else
			{
				// Return a string that contains the code which calls the "conversion" function with the member value.

View on GitHub (pinned to 0418340488)

Solutions

1. Add MethodName to the [CreateFromString] attribute, pointing to the static method that performs string-to-type conversion.
2. Ensure the method name is correct and the method exists as a public static method on the type.
3. Follow the existing pattern from other [CreateFromString]-decorated types in the codebase.

Example fix

// before
[CreateFromString]
public class MyType { ... }
// after
[CreateFromString(MethodName = nameof(Parse))]
public class MyType
{
    public static MyType Parse(string value) { ... }
}

// Verify [CreateFromString] has MethodName before using the type in XAML:
// var attr = typeof(MyType).GetCustomAttribute<CreateFromStringAttribute>();
// if (attr == null || string.IsNullOrEmpty(attr.MethodName))
//     Console.WriteLine("[CreateFromString] must specify MethodName");

When it happens

Trigger: A type is decorated with [CreateFromString] but the MethodName property of the attribute is not set, or the attribute instance is malformed — e.g. [CreateFromString] with no arguments, or with other named arguments but not MethodName.

Common situations: A custom XAML type converter type was decorated with [CreateFromString] incompletely; the attribute was copied from an example without filling in MethodName; the attribute definition changed and MethodName is no longer defaulted.

Related errors

• context
• Value must be non-null string.
• Conversion from type {0} is not supported
• Conversion to type {0} is not supported
• Cannot cast object '{0}' to string

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/9ff3438e9524d547. Report an issue: GitHub.