dotnet/wpf · warning · NotSupportedException

The only IPersistFile operation supported by the component…

Error message

The only IPersistFile operation supported by the component is Load.

What it means

IPersistStream.GetSizeMax must return the size needed to persist the object, but the filter does not use this interface for persistence, so it throws NotSupportedException reusing the SR.FilterIPersistFileIsReadOnly message. It is an unsupported-operation stub rather than a state error.

Solutions

Do not call GetSizeMax on the filter; it never saves via IPersistStream
Catch NotSupportedException around GetSizeMax for read-only components
Restructure persistence code to detect load-only components and skip save protocols

Example fix

// before
((IPersistStream)filter).GetSizeMax(out long size);
// after
try { ((IPersistStream)filter).GetSizeMax(out long size); }
catch (NotSupportedException)
{
    // read-only filter: skip IPersistStream save protocol
}

Defensive patterns

Strategy: try-catch

Try / catch

try { ((IPersistStream)filter).GetSizeMax(out long size); }
catch (NotSupportedException)
{ /* unsupported on read-only filter; skip save protocol */ }

Prevention

Do not call GetSizeMax on filters
Detect load-only persistence components before invoking save-side methods
Wrap generic persistence protocols in capability checks

When it happens

Trigger: Calling IPersistStream.GetSizeMax(out pcbSize) on an XpsFilter instance.

Common situations: Marshaled clients that call GetSizeMax before Save in a standard persistence protocol; reflection-based test coverage of IPersistStream.

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/4ec24b8339e06b78. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/IO/Packaging/XpsFilter.cs:589

        /// <param name="stream">The stream to which the object is saved. </param>
        /// <param name="fClearDirty">Indicates whether the dirty state is to be cleared. </param>
        /// <remarks>
        /// Expected error codes are described at
        /// http://msdn.microsoft.com/library/default.asp?url=/library/en-us/com/html/b748b4f9-ef9c-486b-bdc4-4d23c4640ff7.asp
        /// </remarks>
        void IPersistStream.Save(MS.Internal.Interop.IStream stream, bool fClearDirty)
        {
            throw new COMException(SR.FilterIPersistStreamIsReadOnly, NativeMethods.STG_E_CANTSAVE);
        }

        /// <summary>
        /// The purpose of this function when implemented by a persistent object is to return
        /// the size in bytes of the stream needed to save the object.
        /// Always returns COR_E_NOTSUPPORTED insofar as the filter does not use this interface for persistence.
        /// </summary>
        void IPersistStream.GetSizeMax(out Int64 pcbSize)
        {
            throw new NotSupportedException(SR.FilterIPersistFileIsReadOnly);
        }

        #endregion IPersistStream methods

        #region Private methods

        /// <summary>
        /// Shared implementation for releasing package/encryptedPackage and underlying stream
        /// </summary>
        private void ReleaseResources()
        {
            if (_encryptedPackage != null)
            {
                _encryptedPackage.Close();
                _encryptedPackage = null;
            }
            else
            {

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