dotnet/wpf · error · FileFormatException

SR.XpsValidatingLoaderDuplicateReference

Error message

SR.XpsValidatingLoaderDuplicateReference

What it means

XPSS0ValidatingLoader.UriHitHandler throws FileFormatException (SR.XpsValidatingLoaderDuplicateReference) when the same resource URI is referenced from two different markup nodes in a schema that forbids multiple references to one URI (e.g. the FixedPage schema). Each target URI may be used from a single node; a second hit from a different node is a format violation.

Solutions

  1. Create a separate resource part (and relationship) for each element needing the resource.
  2. Rewrite markup so each URI reference originates from only one node.
  3. Regenerate the XPS with a compliant producer that follows the single-reference rule.
  4. If reuse is intended, store the resource under a schema/MIME type that allows multiple references.

Example fix

// before
<Image Source="/resources/1.png"/><Image Source="/resources/1.png"/> <!-- same URI twice -->

// after
<Image Source="/resources/1.png"/><Image Source="/resources/2.png"/> <!-- duplicate part per reference -->
Defensive patterns

Strategy: validation

Validate before calling

// detect reused source URIs within a FixedDocument before loading
var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
foreach (var src in pageXml.Descendants().Select(e => (string)e.Attribute("Source")).Where(s => s != null))
    if (!seen.Add(src)) throw new InvalidOperationException($"Duplicate resource reference: {src}");

Try / catch

try
{
    obj = loader.Load(stream, parentUri, pc, mimeType);
}
catch (FileFormatException ex)
{
    // duplicate reference: deduplicate parts or split references before retry
}

Prevention

When it happens

Trigger: Loading an XPS part in strict document mode where _uniqueUriRef already contains the URI under a different node id ((int)_uniqueUriRef[uri] != node, XPSS0ValidatingLoader.cs:214) while XpsSchema.AllowsMultipleReferencesToSameUri is false for that MIME type.

Common situations: Hand-authored or third-party-generated XPS that reuses one image/font relationship from multiple elements; a generator bug sharing a single relationship instead of creating separate parts; package-merge tools that deduplicate resources without adjusting references.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/f10bb8b5bfcd677f. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/XPSS0ValidatingLoader.cs:214

            }
        }


        internal static void AssertDocumentMode()
        {   // Once switched to document mode, we stay there
            _documentMode = true;
        }


        internal void UriHitHandler(int node,Uri uri)
        {
            if (_uniqueUriRef != null)
            {
                if (_uniqueUriRef.Contains(uri))
                {
                    if ((int)_uniqueUriRef[uri] != node)
                    {
                        throw new FileFormatException(SR.XpsValidatingLoaderDuplicateReference);
                    }
                }
                else
                {
                    _uniqueUriRef.Add(uri, node);
                }
            }
            Hashtable validResources = _validResources.Peek();
            if (validResources!=null)
            {
                if (!validResources.ContainsKey(uri))
                {
                    // The hashtable is case sensitive, packuris are not, so if we do not find in hashtable,
                    // do true comparison and add when found for next time...
                    bool found = false;
                    foreach (Uri resUri in validResources.Keys)
                    {
                        if (PackUriHelper.ComparePackUri(resUri,uri) == 0)

View on GitHub (pinned to 81131a70a4)