dotnet/wpf · error

SR.UnknownIndexType

Error message

SR.UnknownIndexType

What it means

The IntegerCollection BAML record encodes an IntegerCollectionType describing how values follow the count in the stream. DeserializeFrom switches on that type; an unrecognized type value means the binary payload does not conform to the known format, so ArgumentException(SR.UnknownIndexType) is thrown. This code path is compiled only under PBTCOMPILER.

Solutions

1. Recompile the XAML/BAML with the same WPF version the runtime uses.
2. Inspect the binary payload's type byte and confirm it is a supported IntegerCollectionType.
3. If handling untrusted input, pre-validate the type byte before deserialization and reject unknown values.

byte typeByte = data[4]; // after Int32 count
if (!Enum.IsDefined(typeof(IntegerCollectionType), typeByte))
    throw new InvalidDataException($"Unknown IntegerCollectionType {typeByte}");

try { obj = serializer.ConvertCustomBinaryToObject(data); }
catch (ArgumentException ex) { LogCorruptBaml(ex); return null; }

When it happens

Trigger: ConvertCustomBinaryToObject / StaticConvertCustomBinaryToObject encounters an IntegerCollection whose IntegerCollectionType byte is not one of the supported enum values (e.g. data produced by a newer/older compiler).

Common situations: Cross-version BAML incompatibility, hand-modified compiled resources, fuzzed or adversarial binary input to a XAML deserializer.

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

• SR.IntegerCollectionLengthLessThanZero
• Unrecognized float type in BAML file.
• Can't Assign to Known Type attributes
• Could not find prefix for type
• Drawing Attribute tag embedded in ISF stream does not match…

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/6aee9db94137aea0. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/XamlInt32CollectionSerializer.cs:324

                        {                    
                            theCollection.Add( (int) reader.ReadUInt16()); 
                        }
                    }
                    break; 
                        
                    case IntegerCollectionType.Integer : 
                    {                    
                        for ( int i = 0; i < count; i++ ) 
                        {                    
                            int value = reader.ReadInt32(); 

                            theCollection.Add( value);
                        }                            
                    }                            
                    break; 
                    
                    default:
                        throw new ArgumentException(SR.UnknownIndexType); 
                }
            }

            return theCollection; 
        }
#endif

#endregion Conversions

        internal enum IntegerCollectionType : byte
        {
            Unknown = 0,
            Consecutive = 1,
            Byte = 2, 
            UShort= 3, 
            Integer=  4
        }
    }

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