dotnet/wpf · error · ArgumentException

SR.UnknownDocumentProperty (fmtid, propId)

Error message

SR.UnknownDocumentProperty (fmtid, propId)

What it means

ArgumentException with message UnknownDocumentProperty(fmtid, propId) (paramName 'propId') thrown by StorageBasedPackageProperties.GetVtFromPropId when the property-set lookup table has no entry mapping the given fmtid/propId combination to a VARTYPE. vtExpected relies on this mapping, so an unmapped property id cannot be read.

Solutions

  1. Only request well-known package properties via PackageProperties.
  2. If supporting custom ids, add a case to GetVtFromPropId returning the correct VARTYPE.
  3. Use a dedicated OLE property-set library for arbitrary custom properties instead of this mapping.
  4. Check the fmtid/propId spelling — a wrong constant lookup triggers the default case.

Example fix

// before
vt = GetVtFromPropId(fmtid, (PropertyId)0x9999); // throws
// after
if (Enum.IsDefined(typeof(PropertyId), propId) && IsKnownProperty(fmtid, propId))
    vt = GetVtFromPropId(fmtid, propId);
else
    return null; // skip unknown property
Defensive patterns

Strategy: validation

Validate before calling

if (!Enum.IsDefined(typeof(PropertyId), propId)) return null; // skip unknown property

Try / catch

try { vt = GetVtFromPropId(fmtid, propId); }
catch (ArgumentException ex) when (ex.ParamName == "propId") { return null; /* unmapped property */ }

Prevention

When it happens

Trigger: Calling GetOleProperty (via a PackageProperties getter) with a propId that exists in the property stream but is not one of the well-known ids (Title, Subject, Author, Keywords, etc.) handled by the switch — including unknown ids under the SummaryInformation or DocumentSummaryInformation format ids.

Common situations: Extending the properties reader to custom property ids without registering them; files carrying extra properties that internal code iterates and tries to resolve.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ff7288ef712d5ed1. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/MS/Internal/IO/Packaging/StorageBasedPackageProperties.cs:824

            {
                switch (propId)
                {
                    case PropertyId.Title:
                    case PropertyId.Subject:
                    case PropertyId.Creator:
                    case PropertyId.Keywords:
                    case PropertyId.Description:
                    case PropertyId.LastModifiedBy:
                    case PropertyId.Revision:
                        return VARTYPE.VT_LPSTR;

                    case PropertyId.LastPrinted:
                    case PropertyId.DateCreated:
                    case PropertyId.DateModified:
                        return VARTYPE.VT_FILETIME;

                    default:
                        throw new ArgumentException(
                            SR.Format(SR.UnknownDocumentProperty, fmtid.ToString(), propId),
                            nameof(propId)
                            );
                }
            }
            else if (fmtid == FormatId.DocumentSummaryInformation)
            {
                switch (propId)
                {
                    case PropertyId.Category:
                    case PropertyId.Identifier:
                    case PropertyId.ContentType:
                    case PropertyId.Language:
                    case PropertyId.Version:
                    case PropertyId.ContentStatus:
                        return VARTYPE.VT_LPSTR;

                    default:

View on GitHub (pinned to 81131a70a4)