unoplatform/uno · error · ArgumentNullException

xamlNamespace

Error message

xamlNamespace

What it means

Thrown by XamlSchemaContext.GetAllXamlTypes when the xamlNamespace argument is null. GetAllXamlTypes enumerates all XamlTypes registered under a given XAML namespace; a null namespace cannot index the internal dictionary, so it fails fast with an ArgumentNullException.

Source

Thrown at src/SourceGenerators/System.Xaml/System.Xaml/XamlSchemaContext.cs:176

		{
			lock (gate)
			{
				if (xaml_nss == null)
				{
					xaml_nss = new Dictionary<string, string>();
					foreach (var ass in AssembliesInScope)
						FillXamlNamespaces(ass);
				}
				return xaml_nss.Values.Distinct();
			}
		}

		public virtual ICollection<XamlType> GetAllXamlTypes (string xamlNamespace)
		{
			lock (gate)
			{
				if (xamlNamespace == null)
					throw new ArgumentNullException("xamlNamespace");
				if (all_xaml_types == null)
				{
					all_xaml_types = new Dictionary<string, List<XamlType>>();
					foreach (var ass in AssembliesInScope)
						FillAllXamlTypes(ass);
				}

				List<XamlType> l;
				if (all_xaml_types.TryGetValue(xamlNamespace, out l))
					return l;
				else
					return empty_xaml_types;
			}
		}

		public virtual string GetPreferredPrefix (string xmlns)
		{
			lock (gate)

View on GitHub (pinned to 0418340488)

Solutions

1. Pass a non-null namespace string to GetAllXamlTypes.
2. Null-check the namespace at the source (the lookup that produced it) before forwarding.
3. Return early or use a sentinel/empty string if the namespace is optional in your flow.

Example fix

// before
var types = ctx.GetAllXamlTypes(ns); // ns may be null
// after
if (ns != null)
    var types = ctx.GetAllXamlTypes(ns);

if (string.IsNullOrEmpty(xamlNamespace))
    throw new InvalidOperationException("xamlNamespace must be non-null before calling GetAllXamlTypes.");
var types = ctx.GetAllXamlTypes(xamlNamespace);

When it happens

Trigger: Calling `schemaContext.GetAllXamlTypes(null)` — typically from code that derived a namespace string that came back null (e.g. a lookup that returned null and was not checked).

Common situations: Programmatic callers passing an unresolved namespace; helper methods forwarding a nullable namespace without null-checking; test code passing null deliberately.

Related errors

• xmlns
• xamlTypeName
• schemaContext
• The {0} string passed in the colorString argument is not a r
• The {0} string passed in the colorString argument is not a r

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/3e1f07d2a14adc2b. Report an issue: GitHub.