dotnet/wpf · error

SR.Format(SR.ParserBamlEvent, eventName)

Error message

SR.Format(SR.ParserBamlEvent, eventName)

What it means

Like WriteRoutedEvent, WriteEvent throws NotSupportedException(SR.Format(SR.ParserBamlEvent, eventName)) when the build excludes CLR-event BAML record support. The writer cannot encode ordinary CLR events into BAML in that configuration, so the call is refused at runtime.

Solutions

1. Rebuild/use PresentationFramework with the CLR-event BAML record support enabled.
2. Remove or transform CLR event attributes in the source XAML before BAML serialization.
3. Handle the NotSupportedException and serialize such documents as XAML text instead.

Example fix

// before
writer.WriteEvent("MouseDown", "Handler");
// after
// attach the handler in code instead of BAML:
element.MouseDown += Handler;

// Pre-scan XAML for CLR event attributes (AttributeSyntax="Handler") before BAML serialization:
bool hasClrEvents = xamlNodes.Any(n => n.Members.Any(m => m.IsEvent));

try { writer.WriteEvent(eventName, handlerName); }
catch (NotSupportedException ex) when (ex.Message.Contains("event"))
{
    // fall back to XAML text output or skip the event record
}

When it happens

Trigger: Calling WriteEvent on a build with the CLR-event BAML record path compiled out; serializing XAML that contains CLR event attributes (e.g. MouseDown="Handler" on a non-routed event) through BamlWriter in that build.

Common situations: Custom BAML serialization pipelines in stripped WPF builds encountering event attributes; migration of serializers across build flavors with different #if settings.

Related errors

• SR.Format(SR.ParserBamlEvent, eventIdName)
• By default, ToolTip property does not support ToolTip…
• Can't Assign to Known Type attributes
• Cannot convert from type.
• Cannot convert to type.

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/4480f9075df0909b. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/BamlWriter.cs:930

        /// is included here for completeness and future expandability.
        /// </remarks>
        public void WriteEvent(
            string    eventName,
            string    handlerName)
        {
#if EVENTSUPPORT            
            VerifyWriteState();

            XamlClrEventNode eventNode = new XamlClrEventNode(
                                                  0,
                                                  0,
                                                  _depth,
                                                  eventName,
                                                  null,
                                                  handlerName);
            _bamlRecordWriter.WriteClrEvent(eventNode);
#else
            throw new NotSupportedException(SR.Format(SR.ParserBamlEvent, eventName));
#endif
        }

#endregion Record Writing

#region Internal Methods

    /***************************************************************************\
    *
    * BamlWriter.ProcessMarkupExtensionNodes
    *
    * Write out baml records for all the xamlnodes contained in the buffered
    * markup extension list.
    * NOTE:  This list must contain only xamlnodes that are known to be part of
    *        MarkupExtensions.  This is NOT a general method to handle all types
    *        of xaml nodes.
    *
    \***************************************************************************/

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