dotnet/wpf · error · InvalidOperationException

SR.ParserTypeConverterTextNeedsEndElement

Error message

SR.ParserTypeConverterTextNeedsEndElement

What it means

InvalidOperationException with SR.ParserTypeConverterTextNeedsEndElement thrown when pending TypeConverter text was written but instead of the matching end element the parser encounters a new element start (e.g. a nested element), so the buffered text can never be processed as the element's conversion input.

Solutions

Close the text-only element before starting any child element: move the child element outside the parent.
If the parent should contain children, don't rely on TypeConverter text — set the text via a property element or attribute.
Verify closing tags match the correct elements to avoid stray nesting.
Simplify the markup so each element has either text content or element children, never text + children mixed.

Example fix

// before
<FontFamily>Symbol<Button/></FontFamily>
// after
<FontFamily>Symbol</FontFamily>
<Button/>

Defensive patterns

Strategy: validation

Validate before calling

// text-only elements must not contain child elements
bool hasText = el.Nodes().OfType<XText>().Any(n => !string.IsNullOrWhiteSpace(n.Value));
if (hasText && el.Elements().Any()) throw new InvalidOperationException($"<{el.Name}> has text content plus child elements");

Try / catch

try { return (T)XamlReader.Parse(xaml); } catch (InvalidOperationException ex) when (ex.Message.Contains("end")) { log.Error(ex.Message); throw; }

Prevention

Close text-only elements before opening child elements.
Never nest elements inside a TypeConverter-text element.
Lint generated XAML for mixed text/element content.

When it happens

Trigger: Parsing XAML like <FontFamily>Symbol<Button/></FontFamily> — text content followed by a child element before the parent's end tag, while the type-converter decision machinery expects the end element to flush the text.

Common situations: Accidentally nesting elements inside an element whose content is plain text for a TypeConverter (typo in markup, wrong closing tag, copy/paste of children into a text-only element).

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/8b7dd632847a6b10. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/XamlReaderHelper.cs:6165

                {
                    // We've just seen the InitializationString, we expect it to be immediately
                    //  followed by an ElementEnd.
                    if( xamlNode.TokenType == XamlNodeType.ElementEnd )
                    {
                        Debug.Assert(((XamlNode)_xamlNodes[_typeConverterCandidateIndex]).TokenType==XamlNodeType.ElementStart,
                            "We've lost track of the ElementStart node, and we're about to die with a cast exception.  See if the ElementStart is still in the ArrayList somewhere, and find out why the pointer got out of sync.");

                        // We've seen the full <ElementStart>InitializationText</ElementEnd> sequence.
                        ((XamlElementStartNode)_xamlNodes[_typeConverterCandidateIndex]).CreateUsingTypeConverter = true;

                        // The initializationString would be used as input to the candidate element's TypeConverter.
                        _typeConverterTextWrittenAndNotProcessed = null;
                    }
                    else
                    {
                        // Example that would trip this error:
                        //  <FontFamily>Symbol<Button/></FontFamily>
                        throw new InvalidOperationException(SR.Format(SR.ParserTypeConverterTextNeedsEndElement, _typeConverterTextWrittenAndNotProcessed));
                    }

                    // One set of XamlNodes for TypeConverter done, start watching for another.
                    ResetTypeConverterDecision();
                }
                return;
            }

            // Checking the given XamlNode against the list of types that we know will
            //  break our ability to use TypeConverter.
            private bool NodeTypePrecludesTypeConverterUse(XamlNode xamlNode)
            {
                XamlNodeType tokenType = xamlNode.TokenType;

                switch(tokenType)
                {
                    /////////////////////////////////////////////////////////////
                    //

View on GitHub (pinned to 81131a70a4)