What causes "SR.Format(SR.InvalidNamespace, xmlNamespace)" in dotnet/wpf?

Pass a proper namespace Uri string, e.g., "http://schemas.example.com/my-annotations".

dotnet/wpf · error · ArgumentException

SR.Format(SR.InvalidNamespace, xmlNamespace)

Error message

SR.Format(SR.InvalidNamespace, xmlNamespace)

What it means

IsXmlNamespaceSupported (AddIgnoredNamespace path) throws ArgumentException (SR.InvalidNamespace) when the xmlNamespace string supplied is not empty but is not a well-formed absolute or relative Uri. Ignored namespaces must be valid Uri strings.

Solutions

Pass a proper namespace Uri string, e.g., "http://schemas.example.com/my-annotations".
Uri-escape invalid characters before calling (Uri.EscapeDataString for components).
Pre-check with Uri.IsWellFormedUriString(ns, UriKind.RelativeOrAbsolute) and skip or fix invalid values.
If you intend to ignore nothing, call nothing - empty/null strings are accepted as no-ops.

Example fix

// before
store.AddIgnoredNamespace("my custom namespace");

// after
store.AddIgnoredNamespace("http://schemas.example.com/my-annotations");

Defensive patterns

Strategy: validation

Validate before calling

if (!string.IsNullOrEmpty(ns) && !Uri.IsWellFormedUriString(ns, UriKind.RelativeOrAbsolute))
    throw new ArgumentException($"Invalid namespace: {ns}");

Type guard

bool IsValidNamespace(string ns) => string.IsNullOrEmpty(ns) || Uri.IsWellFormedUriString(ns, UriKind.RelativeOrAbsolute);

Try / catch

try { store.AddIgnoredNamespace(ns); }
catch (ArgumentException ex) when (ex.ParamName == "xmlNamespace") { log.Warn($"Skipping invalid ignored namespace: {ns}"); }

Prevention

Always pass full namespace Uri strings, not display names.
Validate namespace strings with Uri.IsWellFormedUriString before calling AddIgnoredNamespace.
Escape dynamic components with Uri.EscapeDataString instead of string concatenation.

When it happens

Trigger: Calling XmlStreamStore.AddIgnoredNamespace(xmlNamespace) with a non-empty string that fails Uri.IsWellFormedUriString, e.g., containing spaces or illegal characters like "my namespace" or "<test>".

Common situations: Passing a human-readable label instead of a namespace Uri; config values with unencoded spaces; typos in namespace strings; concatenating strings to build a namespace and forgetting Uri.EscapeDataString.

Understand the failure class

Background: "Invalid URL" errors: why new URL(), URI.parse, and reqwest::Url reject your string — missing scheme, whitespace, and bad path format — this error's family across 39 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/89b40c32e19e9413. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Annotations/Storage/XmlStreamStore.cs:879

            return reader;
        }

        /// <summary>
        /// A callback for XmlCompatibilityReader
        /// </summary>
        /// <param name="xmlNamespace">inquired namespace</param>
        /// <param name="newXmlNamespace">the newer subsumming namespace</param>
        /// <returns>true if the namespace is known, false if not</returns>
        /// <remarks>This API always returns false because all known namespaces are registered
        /// before loading the Xml. It stores the namespace as ignored.</remarks>
        private bool IsXmlNamespaceSupported(string xmlNamespace, out string newXmlNamespace)
        {
            //store the namespace if needed
            if (!String.IsNullOrEmpty(xmlNamespace))
            {
                if (!Uri.IsWellFormedUriString(xmlNamespace, UriKind.RelativeOrAbsolute))
                {
                    throw new ArgumentException(SR.Format(SR.InvalidNamespace, xmlNamespace), nameof(xmlNamespace));
                }
                Uri namespaceUri = new Uri(xmlNamespace, UriKind.RelativeOrAbsolute);
                if (!_ignoredNamespaces.Contains(namespaceUri))
                    _ignoredNamespaces.Add(namespaceUri);
            }

            newXmlNamespace = null;
            return false;
        }



        /// <summary>
        ///     Selects the annotation XmlElement from the current document
        ///     with the given id.
        /// </summary>
        /// <param name="id">the id to query for in the XmlDocument</param>
        /// <returns>the XmlElement representing the annotation with the given id</returns>

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