AvaloniaUI/Avalonia · error · ExpressionParseException

Expected ' '.

Error message

Expected '{close}'.

What it means

ArgumentListParser.ParseArguments throws ExpressionParseException("Expected '{close}'.") at line 47 when the read loop exits (reader exhausted) without ever consuming the close bracket. The argument list started correctly but was never closed before end of input.

Solutions

1. Close the indexer with the matching `]` after the last argument.
2. When assembling paths programmatically, always append the close bracket.

Example fix

// before
{Binding Matrix[0,1}
// after
{Binding Matrix[0,1]}

// Same terminated check as [175]: ensure the close bracket exists for multi-arg indexers.
static bool IndexerIsTerminated(string path)
{
    int open = path.IndexOf('[');
    if (open < 0) return true;
    return path.IndexOf(']', open) >= 0;
}
if (!IndexerIsTerminated(path)) throw new ArgumentException("Unterminated indexer.");

try { var nodes = BindingExpressionGrammar.Parse(path); }
catch (ExpressionParseException ex) when (ex.Message.Contains("Expected"))
{ /* add the missing ']' */ }

When it happens

Trigger: An indexer argument list spanning multiple arguments that runs off the end of the string without a closing bracket, e.g. `Items[0,1`.

Common situations: Truncated multi-argument indexer paths; dynamic path building that omits the final bracket; XAML truncation.

Related errors

• Expected ' '.
• Expected indexer argument.
• Expected end of expression.
• Expected ' '.
• Could not convert list index

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/8dde692612306bc9. Report an issue: GitHub.

Appendix: source

Thrown at src/Avalonia.Base/Data/Core/Parsers/ArgumentListParser.cs:47

                    {
                        throw new ExpressionParseException(r.Position, $"Expected '{delimiter}'.");
                    }
                    else if (r.TakeIf(close))
                    {
                        return result;
                    }
                    else
                    {
                        if (r.Take() != delimiter)
                        {
                            throw new ExpressionParseException(r.Position, $"Expected '{delimiter}'.");
                        }

                        r.SkipWhitespace();
                    }
                }

                throw new ExpressionParseException(r.Position, $"Expected '{close}'.");
            }

            throw new ExpressionParseException(r.Position, $"Expected '{open}'.");
        }
    }
}

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