dotnet/wpf · error · InvalidOperationException

Invalid ISF tag logic

Error message

Invalid ISF tag logic

What it means

The tag switch in DecodeRawISF has a default case that throws InvalidOperationException, meaning the decoder encountered an ISF tag value it has no handler for. Unlike the ArgumentException guards (which detect size/consistency problems), this indicates the tag itself is outside the set the decoder understands — malformed or unsupported ISF data, or an internal logic gap.

Solutions

1. Regenerate the ISF with a writer compatible with the consuming WPF version.
2. Update to a newer .NET/WPF runtime whose decoder handles the tag in question.
3. Locate the offending tag bytes (compare with a known-good payload) to identify corruption.
4. Catch InvalidOperationException around DecodeISF and treat the stream as unsupported rather than crashing the app.

Example fix

// before
var strokes = StrokeCollectionSerializer.DecodeISF(stream); // unhandled tag crashes
// after
try { var strokes = StrokeCollectionSerializer.DecodeISF(stream); }
catch (InvalidOperationException ex) { Log.Warn("Unsupported ISF tag", ex); strokes = new StrokeCollection(); }

try { return DecodeISF(stream); } catch (InvalidOperationException ex) { logger.Warn(ex, "Unsupported/unknown ISF tag"); return new StrokeCollection(); }

When it happens

Trigger: Decoding an ISF stream containing a tag not covered by any case in the DecodeRawISF switch (e.g. a newer/proprietary ISF tag, corrupt bytes flipping a tag value, or an unhandled valid tag).

Common situations: ISF produced by newer or non-Microsoft ink implementations using tags this WPF version doesn't know; bit-corrupted tag values; loading ISF on an older .NET/WPF version than the writer.

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

• Buffer range is smaller than expected expected size
• Button data length not equal to expected length
• Drawing Attribute tag embedded in ISF stream does not match…
• Empty data to load
• ExtendedProperty decoded totalBytesInStrokeBlockOfIsfStream…

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/4fd9a2e76fcf83a2. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/Ink/InkSerializedFormat/InkSerializer.cs:660

                                        // Load the stroke
                                        Stroke localStroke;
#if OLD_ISF
                                        localBytesDecoded = StrokeSerializer.DecodeStroke(inputStream, bytesDecodedInCurrentTag, guidList, strokeDescriptor, currentStylusPointDescription, activeDrawingAttributes, currentTabletToInkTransform, compressor, out localStroke);
#else
                                        localBytesDecoded = StrokeSerializer.DecodeStroke(inputStream, bytesDecodedInCurrentTag, guidList, strokeDescriptor, currentStylusPointDescription, activeDrawingAttributes, currentTabletToInkTransform, out localStroke);
#endif

                                        if (localStroke != null)
                                        {
                                            _coreStrokes.AddWithoutEvent(localStroke);
                                            strokeIndex++;
                                        }
                                        break;
                                    }

                                default:
                                    {
                                        throw new InvalidOperationException(ISFDebugMessage("Invalid ISF tag logic"));
                                    }
                            }

                            // if this isfTag's decoded size != expected size, then error out
                            if (localBytesDecoded != bytesDecodedInCurrentTag)
                            {
                                throw new ArgumentException(ISFDebugMessage("Invalid ISF data"));
                            }

                            break;
                        }

                    case KnownTagCache.KnownTagIndex.Transform:
                    case KnownTagCache.KnownTagIndex.TransformIsotropicScale:
                    case KnownTagCache.KnownTagIndex.TransformAnisotropicScale:
                    case KnownTagCache.KnownTagIndex.TransformRotate:
                    case KnownTagCache.KnownTagIndex.TransformTranslate:
                    case KnownTagCache.KnownTagIndex.TransformScaleAndTranslate:

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