dotnet/wpf · error · XpsSerializationException

Serialization of this type of object is not supported.

Error message

Serialization of this type of object is not supported.

What it means

XpsFontSerializationService.SignalCommit maps a document-structure type to a FontSubsetterCommitPolicies value; only FixedDocumentSequence, FixedDocument, FixedPage, and Visual are recognized. Any other Type (or null) falls into the else branch and throws XpsSerializationException with ReachSerialization_NotSupported. Callers invoke it when releasing font subsets at commit points (signalReleaseToFontService, ReleaseXmlWriter).

Solutions

Pass exactly typeof(FixedDocumentSequence), typeof(FixedDocument), typeof(FixedPage), or typeof(Visual) — not derived types (the comparisons use ==).
Null-check the type argument before calling SignalCommit.
Catch XpsSerializationException and default to CommitPerPage for unknown types in custom pipelines.

Example fix

// before
fontService.SignalCommit(page.GetType()); // may be a derived page type

// after
fontService.SignalCommit(typeof(FixedPage)); // exact type required by SignalCommit

Defensive patterns

Strategy: type-guard

Validate before calling

static readonly Type[] CommitTypes =
    { typeof(FixedDocumentSequence), typeof(FixedDocument), typeof(FixedPage), typeof(Visual) };
bool ok = type != null && CommitTypes.Contains(type);
if (!ok) throw new ArgumentException("SignalCommit requires an exact XPS content type.");

Type guard

static bool IsCommittableType(Type type) =>
    type == typeof(FixedDocumentSequence) || type == typeof(FixedDocument) ||
    type == typeof(FixedPage) || type == typeof(Visual);

Try / catch

try
{
    fontService.SignalCommit(type);
}
catch (XpsSerializationException ex) when (ex.Message.Contains("not supported"))
{
    // fall back to per-page commit: _fontSubsetter.CommitFontSubsetsSignal(CommitPerPage)
}

Prevention

Pass typeof(...) constants, never GetType() of possibly derived instances (checks use ==).
Null-check the type before calling.
Map derived page/document classes to their exact XPS base type first.

When it happens

Trigger: SignalCommit called with a type other than typeof(FixedDocumentSequence), typeof(FixedDocument), typeof(FixedPage), or typeof(Visual) — e.g. passing typeof(FixedPage) via a derived page type variable that is not exactly one of these (the check uses ==, not inheritance), or passing a null Type.

Common situations: Custom serialization loops calling SignalCommit with a content-element subtype (checks are exact reference equality against typeof, so subclasses fail); null type after a failed content lookup; extending the XPS model with custom container types.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/7022cd72078693f1. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/ReachFramework/Serialization/XpsFontSerializationService.cs:58

            if(type == typeof(FixedDocumentSequence))
            {
                signal = FontSubsetterCommitPolicies.CommitEntireSequence;
            }
            else if(type ==  typeof(FixedDocument))
            {
                signal = FontSubsetterCommitPolicies.CommitPerDocument;
            }
            else if(type== typeof(FixedPage))
            {
                signal = FontSubsetterCommitPolicies.CommitPerPage;
            }
            else if(type == typeof(Visual))
            {
                signal = FontSubsetterCommitPolicies.CommitPerPage;
            }
            else
            {
                throw new XpsSerializationException(SR.ReachSerialization_NotSupported);
            }
            return _fontSubsetter.CommitFontSubsetsSignal(signal);
        }
        
        /// <summary>
        /// This method retieves a XpsFontSubsetter for
        /// serializing a font to a Xps package. 
        /// This method assumes the font subsetter 
        /// has already been itialized.
        /// </summary>
        /// <returns>
        /// A reference to a XpsFontSubsetter instance.
        /// </returns>
        public 
        XpsFontSubsetter
        FontSubsetter
        {
            get

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