dotnet/wpf · error · ObjectDisposedException

FixedPageReader

Error message

FixedPageReader

What it means

ObjectDisposedException thrown by XpsFixedPageReaderWriter.AddResource when the page's underlying package part (_metroPart) is null, meaning the FixedPage reader/writer has been disposed (or was never backed by a part). You cannot add resources (images, fonts, etc.) to a page after its part has gone away.

Solutions

  1. Call AddResource before Commit()/Dispose of the page writer.
  2. Reorder code so resources (fonts, images) are added while the page is open, then commit last.
  3. Keep the XpsDocument open until all page resources are written.
  4. Remove stale page-writer references once the document is closed; reacquire readers via the document if needed.
  5. Wrap in try-catch for ObjectDisposedException to surface lifecycle bugs during batch generation.

Example fix

// before
page.Commit();
page.AddResource(typeof(XpsImage), imageUri); // throws
// after
page.AddResource(typeof(XpsImage), imageUri);
page.Commit();
Defensive patterns

Strategy: try-catch

Validate before calling

// Track lifecycle: only call while page is open
if (pageCommitted) throw new InvalidOperationException("Page already committed; AddResource is invalid");
// else safe:
pageWriter.AddResource(typeof(XpsImage), imageUri);

Type guard

bool CanMutatePage(IXpsFixedPageReaderWriter page) => page != null && !isCommitted.Contains(page);

Try / catch

try
{
    pageWriter.AddResource(resourceType, resourceUri);
}
catch (ObjectDisposedException ex) when (ex.ObjectName == "FixedPageReader")
{
    throw new InvalidOperationException("Resources must be added before page Commit(). Reorder the pipeline.", ex);
}

Prevention

When it happens

Trigger: Calling AddResource(Type resourceType, Uri resourceUri) after Commit()ing or disposing the page writer, or on a reader obtained from a closed/disposed XpsDocument.

Common situations: Retaining IXpsFixedPageReaderWriter references in collections after the document was closed; adding resources in a deferred/background step that runs after page commit; using statements that dispose the XpsDocument before resource attachment finishes.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/81b7974d588e57b4. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/ReachFramework/Packaging/XpsFixedPageReaderWriter.cs:781

        /// </param>
        /// <param name="resourceUri">
        /// The absolute path to the resouce to be added. If null
        /// a unique resource path will be generated
        /// </param>
        /// <returns>
        /// Returns an XpsResource instance for the newly created resource.
        /// </returns>
        /// <exception cref="ObjectDisposedException">FixedPageReader has already been disposed</exception>
        public
        XpsResource
        AddResource(
            Type        resourceType,
            Uri         resourceUri
            )
        {
            if (null == _metroPart)
            {
                throw new ObjectDisposedException("FixedPageReader");
            }

            //
            // Create the part and writer
            //
            PackagePart metroPart = null;
            if( resourceUri != null )
            {
                metroPart = this.CurrentXpsManager.GetPart(resourceUri);
                if (metroPart == null)
                {
                    metroPart = GeneratePartForResourceType(resourceType, resourceUri);
                }
            }

            XpsResource xpsResource;
            if( resourceType == typeof( XpsImage ) )
            {

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