dotnet/wpf · error · XpsPackagingException

Thumbnails support only JPG and PNG image types.

Error message

Thumbnails support only JPG and PNG image types.

What it means

XpsManager.AddThumbnail validates the requested thumbnail image type and throws XpsPackagingException when the type is neither JpegImageType nor PngImageType. Per the XPS (Open Packaging) specification, thumbnail parts must be JPEG or PNG images; any other XpsImageType is unsupported for thumbnails.

Solutions

1. Pass XpsImageType.JpegImageType or XpsImageType.PngImageType only when calling AddThumbnail.
2. Add an explicit switch/if that maps non-thumbnail image types to JPEG or PNG before calling AddThumbnail.
3. Validate the image type at the call site and refuse invalid values before invoking the API.

Example fix

// before
XpsThumbnail thumb = manager.AddThumbnail(XpsImageType.TiffImageType, node, null);
// after
XpsImageType thumbType = (imageType == XpsImageType.JpegImageType || imageType == XpsImageType.PngImageType)
    ? imageType : XpsImageType.PngImageType;
XpsThumbnail thumb = manager.AddThumbnail(thumbType, node, null);

bool isSupported = imageType == XpsImageType.JpegImageType || imageType == XpsImageType.PngImageType;
if (!isSupported) throw new ArgumentException(nameof(imageType));

bool IsValidThumbnailType(XpsImageType t) => t == XpsImageType.JpegImageType || t == XpsImageType.PngImageType;

catch (XpsPackagingException ex) { /* fall back to PngImageType */ }

When it happens

Trigger: Calling AddThumbnail with an XpsImageType other than JpegImageType or PngImageType (e.g. XpsImageType.TiffImageType or any other image type enum value).

Common situations: Using the same image-type constant used for page images (e.g. TIFF) when also writing a thumbnail; a generic code path that picks an image type from configuration and passes it to AddThumbnail without restricting to JPEG/PNG.

Related errors

• Document PackagePart URI is not valid.
• Only writers can call this method.
• Package must contain an XPS PackagePart.
• PackagePart already has associated Thumbnail.
• PackagePart URI does not correspond to a FixedDocument.

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/1da5dcbcacbe0d9e. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/ReachFramework/Packaging/XpsManager.cs:725

                propertiesPart = GenerateUniquePart(XpsS0Markup.CoreDocumentPropertiesType );
                _metroPackage.CreateRelationship(propertiesPart.Uri, TargetMode.Internal, XpsS0Markup.CorePropertiesRelationshipType );
            }
            return propertiesPart;
        }

        public
        XpsThumbnail
        AddThumbnail(XpsImageType imageType, INode parent, XpsThumbnail oldThumbnail )
        {
            XpsThumbnail newThumbnail = null;
            if( oldThumbnail != null )
            {
                throw new XpsPackagingException(SR.ReachPackaging_AlreadyHasThumbnail);
            }    
            if( !( imageType == XpsImageType.JpegImageType ||
                    imageType == XpsImageType.PngImageType ) )
            {
                throw new XpsPackagingException(SR.ReachPackaging_UnsupportedThumbnailImageType);
            }   
            newThumbnail = new XpsThumbnail(this,
                                        parent,
                                        GenerateUniquePart(ImageTypeToString(imageType))
                                        );
            return newThumbnail;
        }

        public
        XpsThumbnail
        EnsureThumbnail( INode parent, PackagePart part )
        {
            XpsThumbnail thumbnail = null;
            PackagePart thumbNailPart = GetThumbnailPart(part);
            if( thumbNailPart != null )
            {
                thumbnail = new XpsThumbnail(this,
                                            parent,

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