dotnet/wpf · error · XpsPackagingException

PackagePart URI does not correspond to a FixedPage.

Error message

PackagePart URI does not correspond to a FixedPage.

What it means

XpsFixedDocumentReaderWriter.AddPageToCache throws XpsPackagingException (ReachPackaging_NotAFixedPage) when the part at the page URI exists but its validated content type (including sub-type) is not the XPS FixedPage content type. The part found via the relationship is not a FixedPage as required.

Solutions

Correct the relationship target to point at a part with the FixedPage content type ('application/vnd.ms-package.xps-fixedpage').
Fix the part's Content-Type metadata in the package if it is actually a FixedPage but mislabeled.
Regenerate the package with standard XPS writing APIs instead of manual OPC manipulation.
Validate the package structure with a validator before loading.

Defensive patterns

Strategy: validation

Validate before calling

var part = xpsManager.GetPart(pageUri);
if (part == null || !part.ValidatedContentType().AreTypeAndSubTypeEqual(XpsS0Markup.FixedPageContentType))
    throw new Exception("URI is not a FixedPage: " + pageUri);

Try / catch

try { ParsePages(); }
catch (XpsPackagingException ex) when (ex.Message.Contains("FixedPage")) { /* skip/repair mislabeled part */ }

Prevention

Ensure page relationships point only to FixedPage-typed parts.
Use standard XPS writers to produce packages.
Run a package validator before consumption.

When it happens

Trigger: A FixedDocument page relationship points to a part whose validated content type does not equal XpsS0Markup.FixedPageContentType (e.g. it is a FixedDocument, image, or arbitrary part).

Common situations: Hand-built or third-party-generated XPS packages with wrong relationship targets; parts labeled with wrong content types; bugs in XPS conversion tools.

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/8ad4fef6350ba9dc. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/ReachFramework/Packaging/XpsFixedDocumentReaderWriter.cs:980

                    }
                }
            }
        }

        private
        IXpsFixedPageReader
        AddPageToCache( Uri pageUri )
        {
            PackagePart pagePart = CurrentXpsManager.GetPart(pageUri);

            if (pagePart == null)
            {
                 throw new XpsPackagingException(SR.ReachPackaging_PartNotFound);
            }

            if (!pagePart.ValidatedContentType().AreTypeAndSubTypeEqual(XpsS0Markup.FixedPageContentType))
            {
                throw new XpsPackagingException(SR.ReachPackaging_NotAFixedPage);
            }

            //
            // Create the reader/writer for the part
            //
            IXpsFixedPageReader pageReader = new XpsFixedPageReaderWriter(CurrentXpsManager, this, pagePart, null, _pageCache.Count+1);

            //
            // Cache the new reader/writer for later
            //
            _pageCache.Add(pageReader );

            return pageReader;
        }

        private
        void
        EnsureThumbnail()

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