unoplatform/uno · error · ArgumentNullException

serviceProvider

Error message

serviceProvider

What it means

ArgumentNullException thrown by the Reference markup extension's ProvideValue (System.Xaml, ported from Mono) when the IServiceProvider argument is null. Reference (x:Reference) resolves a named element via IXamlNameResolver obtained from the provider, so a null provider makes resolution impossible. Parameter name 'serviceProvider' identifies the null argument.

Source

Thrown at src/SourceGenerators/System.Xaml/System.Windows.Markup/Reference.cs:52

	public class Reference : MarkupExtension
	{
		public Reference ()
		{
		}

		public Reference (string name)
		{
			Name = name;
		}

		[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);
			}

View on GitHub (pinned to 0418340488)

Solutions

1. Always pass the IServiceProvider from the XAML runtime; never invoke ProvideValue without one.
2. In tests, supply a provider whose GetService returns an IXamlNameResolver.
3. Null-check the provider at the call site before invoking.

Example fix

// before
var target = reference.ProvideValue(null);

// after
var target = reference.ProvideValue(xamlServiceProvider);

static object SafeProvide(Reference r, IServiceProvider sp) { if (sp is null) throw new ArgumentNullException(nameof(sp)); return r.ProvideValue(sp); }

static bool HasXamlServices(IServiceProvider sp) => sp?.GetService(typeof(IXamlNameResolver)) is not null;

try { return r.ProvideValue(sp); } catch (ArgumentNullException ex) when (ex.ParamName == "serviceProvider") { throw new InvalidOperationException("x:Reference must be evaluated within a XAML service context."); }

When it happens

Trigger: Calling Reference.ProvideValue(null) directly, e.g. in a unit test or code path that bypasses the XAML runtime supplying the provider.

Common situations: Unit tests invoking ProvideValue without a provider, custom hosting that drops the service context, or misuse of the extension outside markup evaluation.

Related errors

• elements
• arrayType
• serviceProvider
• Name property is not set
• Type property must be set before calling ProvideValue method

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/a258ae3418f6d5d3. Report an issue: GitHub.