dotnet/wpf · error · XamlXmlWriterException

XamlXmlWriterException(SR.Format(SR.XamlXmlWriterWriteNotSup…

Error message

XamlXmlWriterException(SR.Format(SR.XamlXmlWriterWriteNotSupportedInCurrentState, "WriteEndObject"))

What it means

The base WriterState defines WriteEndObject to throw XamlXmlWriterException 'WriteEndObject not supported in current state'. Only states representing an open object element support WriteEndObject; calling it from any other state (no open object, inside a member, after close) throws.

Solutions

  1. Balance every WriteStartObject/WriteGetObject with exactly one WriteEndObject in LIFO order
  2. Track nesting depth in your emitter and assert balance before WriteClose
  3. Fix exception/recovery paths so partial writes are abandoned (new writer) rather than resumed

Example fix

// before
writer.WriteStartObject(type); WriteStartMember(m); WriteEndObject(); // member still open
// after
writer.WriteStartObject(type); WriteStartMember(m); WriteEndMember(); WriteEndObject();
Defensive patterns

Strategy: validation

Validate before calling

if (openObjectDepth <= 0) throw new InvalidOperationException("WriteEndObject without open object");

Try / catch

try { writer.WriteEndObject(); }
catch (XamlXmlWriterException) { /* unbalanced end; restart with fresh writer */ }

Prevention

When it happens

Trigger: Calling WriteEndObject when there is no matching open object — unbalanced End calls, calling WriteEndObject after WriteEndMember closed the value, or calling it twice for one StartObject.

Common situations: Hand-rolled node-stream emitters with mismatched Start/End counters; error-recovery paths that skip EndMember/EndObject calls then continue writing; adapters from other serialization formats mapping element close events naively.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/51b681a70217db34. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlXmlWriter.cs:788

                return prefixMapList;
            }

            private static int CompareByKey(KeyValuePair<string, string> x, KeyValuePair<string, string> y)
            {
                return string.Compare(x.Key, y.Key, false, TypeConverterHelper.InvariantEnglishUS);
            }
        }

        private abstract class WriterState
        {
            public virtual void WriteObject(XamlXmlWriter writer, XamlType type, bool isObjectFromMember)
            {
                throw new XamlXmlWriterException(SR.Format(SR.XamlXmlWriterWriteNotSupportedInCurrentState, "WriteObject"));
            }

            public virtual void WriteEndObject(XamlXmlWriter writer)
            {
                throw new XamlXmlWriterException(SR.Format(SR.XamlXmlWriterWriteNotSupportedInCurrentState, "WriteEndObject"));
            }

            public virtual void WriteStartMember(XamlXmlWriter writer, XamlMember property)
            {
                throw new XamlXmlWriterException(SR.Format(SR.XamlXmlWriterWriteNotSupportedInCurrentState, "WriteStartMember"));
            }

            public virtual void WriteEndMember(XamlXmlWriter writer)
            {
                throw new XamlXmlWriterException(SR.Format(SR.XamlXmlWriterWriteNotSupportedInCurrentState, "WriteEndMember"));
            }

            public virtual void WriteValue(XamlXmlWriter writer, string value)
            {
                throw new XamlXmlWriterException(SR.Format(SR.XamlXmlWriterWriteNotSupportedInCurrentState, "WriteValue"));
            }

            public virtual void WriteNamespace(XamlXmlWriter writer, NamespaceDeclaration namespaceDeclaration)

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