dotnet/wpf · error · XamlObjectReaderException

SR.ObjectReaderMultidimensionalArrayNotSupported

Error message

SR.ObjectReaderMultidimensionalArrayNotSupported

What it means

XamlObjectReader throws this when the object graph contains a multidimensional Array (Rank > 1, e.g. int[,]). XAML markup has no syntax for multidimensional arrays, so such values cannot be round-tripped.

Solutions

Replace multidimensional arrays with jagged arrays (T[][]) which XAML can express
Use a collection-of-collections or a wrapper type (e.g. Matrix class) instead of T[,]
Convert the array to a flat array with known row/col dimensions before reading
Mark the multidimensional array member as not serialized (ignore/visibility attribute)

Example fix

// before
public int[,] Grid { get; set; }
// after
public List<List<int>> Grid { get; set; }

Defensive patterns

Strategy: type-guard

Validate before calling

if (value is Array a && a.Rank > 1) throw new InvalidOperationException("Multidimensional arrays are not XAML-round-trippable");

Type guard

bool IsXamlArray(object v) => v is Array a && a.Rank == 1;

Try / catch

try { using var r = new XamlObjectReader(obj); ... } catch (XamlObjectReaderException ex) when (ex.Message.Contains("MultidimensionalArray")) { /* convert to jagged/collection */ }

Prevention

Prefer jagged arrays or collection-of-collections in serializable models
Wrap matrix data in dedicated types
Check Rank on all Array members before round-tripping

When it happens

Trigger: new XamlObjectReader(obj) (or XamlServices round-trip) where the graph includes a property or collection value of an array with Rank > 1 (ForArray is invoked via ForArray(Array, SerializerContext)).

Common situations: Numeric/grid data (int[,], double[,]) exposed on serializable classes; image/matrix buffers; porting binary-serialized classes to XAML serialization.

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/5020f7bcc15d2f62. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlObjectReader.cs:1806

                    foreach (var ov in propertyInfo.Children)
                    {
                        ((ObjectOrValueMarkupInfo)ov).EnsureNoDuplicateNames(namesInCurrentScope);
                    }
                }
            }

            private static string ConvertTypeAndMethodToString(Type type, string methodName, SerializerContext context)
            {
                string typestring = context.ConvertXamlTypeToString(context.LocalAssemblyAwareGetXamlType(type));

                return $"{typestring}.{methodName}";
            }

            private static ObjectMarkupInfo ForArray(Array value, SerializerContext context)
            {
                if (value.Rank > 1)
                {
                    throw new XamlObjectReaderException(SR.ObjectReaderMultidimensionalArrayNotSupported);
                }

                var type = context.LocalAssemblyAwareGetXamlType(value.GetType());

                var elementType = type.ItemType;

                var items = new MemberMarkupInfo { XamlNode = new XamlNode(XamlNodeType.StartMember, XamlLanguage.Items) };
                foreach (object item in value)
                {
                    items.Children.Add(ForObject(item, context));
                }

                var objectInfo = new ObjectMarkupInfo()
                {
                    XamlNode = new XamlNode(XamlNodeType.StartObject, XamlLanguage.Array),
                    Object = value,
                    // Scope = context.ReferenceTable,
                    Properties =

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