AvaloniaUI/Avalonia · error · ExpressionParseException

Unexpected end of the expression

Error message

Unexpected end of the expression

What it means

Error "Unexpected end of the expression" thrown in AvaloniaUI/Avalonia.

Source

Thrown at src/Avalonia.Base/Rendering/Composition/Expressions/ExpressionParser.cs:258

                var applyUnaryMinus = false;
                while (parser.TryConsume('-')) 
                    applyUnaryMinus = !applyUnaryMinus;

                Expression? parsed;
                
                if (parser.TryConsume('(')) 
                    parsed = ParseTillTerminator(ref parser, ")", false, true, out _);
                else if (parser.TryParseCall(out var functionName))
                {
                    var parameterList = new List<Expression>();
                    while (!parser.TryConsume(')'))
                    {
                        parameterList.Add(ParseTillTerminator(ref parser, ",)", false, true, out var closingToken));
                        if (closingToken == ')')
                            break;
                        if (closingToken != ',')
                            throw new ExpressionParseException("Unexpected end of the expression", parser.Position);
                    }

                    parsed = new FunctionCallExpression(functionName.ToString(), parameterList);
                }
                else if (TryParseAtomic(ref parser, out parsed))
                {
                    // do nothing
                }
                else
                    throw new ExpressionParseException("Unexpected token", parser.Position);

                
                // Parse any following member accesses
                while (parser.TryConsume('.'))
                {
                    if(!parser.TryParseIdentifier(out var memberName))
                        throw new ExpressionParseException("Unexpected token", parser.Position);

View on GitHub (pinned to 11c5427268)

Solutions

1. The expression ends prematurely; add the missing operand or closing parenthesis.
2. Check that string concatenation building the expression did not truncate it.

When it happens

Trigger: Raised when the input ends in the middle of a composition expression construct. Defend by checking for unbalanced parentheses or dangling operators before constructing the animation.

Common situations: See trigger scenarios.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/8d984ca43938554e. Report an issue: GitHub.