dotnet/wpf · error · XamlParseException

SR.MissingComma1 / SR.MissingComma2 (built into 'error')

Error message

SR.MissingComma1 / SR.MissingComma2 (built into 'error')

What it means

In P_NamedArg, a positional or named argument sequence must be comma-separated. When the scanner's current token isn't the expected ',' the parser builds an error via SR.MissingComma1 (after a positional arg) or SR.MissingComma2 (with the current member name and offending token text) and throws XamlParseException.

Solutions

Insert the missing comma between arguments
Use '=' and ',' correctly for named arguments: Path=Text, ElementName=Btn
Check the member/token named in the error message to find the exact split point

Example fix

// before
<TextBlock Text="{Binding Path=Name ElementName=Btn}"/>
// after
<TextBlock Text="{Binding Path=Name, ElementName=Btn}"/>

Defensive patterns

Strategy: validation

Validate before calling

bool ArgumentsCommaSeparated(string s)
{
    // crude pre-check: tokens between '=' assignments must start with ','
    int i = 0;
    while ((i = s.IndexOf('=', i + 1)) > 0)
    {
        int next = s.IndexOf("=", i + 1);
        int comma = s.IndexOf(',', i);
        if (next > 0 && (comma < 0 || comma > next)) return false;
    }
    return true;
}

Try / catch

try { nodes = parser.Parse(meString); }
catch (XamlParseException ex) when (ex.Message.Contains("comma") || ex.Message.Contains("','")) { /* point user to the member named in the message */ }

Prevention

Separate named arguments with ', Name=Value'
Validate argument syntax in editors/snippets
Copy from working examples rather than retyping

When it happens

Trigger: Markup-extension argument lists missing a comma between arguments, e.g. '{StaticResource Foo Bar}' or '{Binding Path=Text ElementName=Btn}' where 'ElementName' needs a preceding comma.

Common situations: Hand-written markup extensions forgetting comma separators, copying positional-style arguments into named-argument form, typos deleting the comma.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/4e89862107cad0af. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/Parser/MePullParser.cs:471

                        yield return node;
                    }

                    f.found = f2.found;
                    break;

                case MeTokenType.PropertyName:
                    {
                        string error;
                        if (_context.CurrentMember is null)
                        {
                            error = SR.Format(SR.MissingComma1,  _tokenizer.TokenText);
                        }
                        else
                        {
                            error = SR.Format(SR.MissingComma2, _context.CurrentMember.Name, _tokenizer.TokenText);
                        }

                        throw new XamlParseException(_tokenizer, error);
                    }

                default:
                    SetBrokenRuleString("NamedArg ::= PROPERTYNAME '=' @(STRING | QUOTEDMARKUPEXTENSION | MarkupExtension)");
                    break;
                }

                yield return Logic_EndMember();
            }
        }

        // ================================================

        private void NextToken()
        {
            _tokenizer.Read();
        }

View on GitHub (pinned to 81131a70a4)