unoplatform/uno · error · InvalidOperationException

serviceProvider does not implement IXamlNameResolver

Error message

serviceProvider does not implement IXamlNameResolver

What it means

Thrown by the Reference markup extension (x:Reference) when ProvideValue cannot obtain an IXamlNameResolver service from the supplied IServiceProvider. The XAML object writer is expected to supply this service so that forward/name references can be resolved at load time. Its absence means the host is not a conforming XAML reader/writer stack.

Source

Thrown at src/SourceGenerators/System.Xaml/System.Windows.Markup/Reference.cs:63

		[ConstructorArgument ("name")]
		public string Name { get; set; }

		public override object ProvideValue (IServiceProvider serviceProvider)
		{
			if (serviceProvider == null)
			{
				throw new ArgumentNullException ("serviceProvider");
			}

			if (Name == null)
			{
				throw new InvalidOperationException ("Name property is not set");
			}

			var r = serviceProvider.GetService (typeof (IXamlNameResolver)) as IXamlNameResolver;
			if (r == null)
			{
				throw new InvalidOperationException ("serviceProvider does not implement IXamlNameResolver");
			}

			var ret = r.Resolve (Name);
			if (ret == null)
			{
				ret = r.GetFixupToken (new string [] {Name}, true);
			}

			return ret;
		}
	}
}

View on GitHub (pinned to 0418340488)

Solutions

Do not call ProvideValue manually; let the XamlObjectWriter / XamlXmlReader pipeline invoke it, which supplies IXamlNameResolver.
If testing, supply a fake IServiceProvider whose GetService returns a IXamlNameResolver implementation for typeof(IXamlNameResolver).
Ensure the XAML schema context has been initialized with a name-scope so the resolver is non-null during load.
Verify x:Reference targets a name that exists within the same namescope.

Example fix

// before
var ext = new Reference { Name = "myBtn" };
var value = ext.ProvideValue(new ServiceLocator()); // throws

// after
var value = ext.ProvideValue(XamlObjectWriterContext.WithNameResolver(resolver));

Defensive patterns

Strategy: validation

Validate before calling

// Validate the service provider before invoking the extension
public static bool CanResolveReference(IServiceProvider sp)
{
    return sp?.GetService(typeof(IXamlNameResolver)) is IXamlNameResolver;
}

// Usage
if (!CanResolveReference(sp)) throw new InvalidOperationException("Name resolver missing");
var value = new Reference { Name = "btn" }.ProvideValue(sp);

Type guard

static bool HasNameResolver(IServiceProvider sp)
    => sp?.GetService(typeof(IXamlNameResolver)) is IXamlNameResolver;

Prevention

Always invoke markup extensions through the XamlObjectWriter pipeline rather than calling ProvideValue directly.
When unit-testing extensions, supply a fake IServiceProvider that advertises IXamlNameResolver.
Treat a null IXamlNameResolver as a host-configuration defect, not a runtime data error.

When it happens

Trigger: Calling Reference.ProvideValue(serviceProvider) where serviceProvider.GetService(typeof(IXamlNameResolver)) returns null. Happens when invoking the markup extension outside a real XAML load context, or with a stub/null service provider that does not advertise name-resolution services.

Common situations: Unit tests that call ProvideValue directly with a mock IServiceProvider; custom XAML writers that forget to register IXamlNameResolver; invoking markup extensions from non-XAML code paths (e.g. manual template instantiation).

Related errors

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/41c1e6886555fc31. Report an issue: GitHub.