AvaloniaUI/Avalonia · error · ExpressionParseException

Unexpected end of expression

Error message

Unexpected end of  expression

What it means

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

Source

Thrown at src/Avalonia.Base/Rendering/Composition/Expressions/ExpressionParser.cs:212

            bool throwOnEnd,
            out char? token)
        {
            ExpressionOperatorGroup left = default;
            token = null;
            while (true)
            {
                if (parser.TryConsumeAny(terminatorChars.AsSpan(), out var consumedToken))
                {
                    if (throwOnTerminator || left.Empty)
                        throw new ExpressionParseException($"Unexpected '{token}'", parser.Position - 1);
                    token = consumedToken;
                    return left.ToExpression();
                }
                parser.SkipWhitespace();
                if (parser.Length == 0)
                {
                    if (throwOnEnd || left.Empty)
                        throw new ExpressionParseException("Unexpected end of  expression", parser.Position);
                    return left.ToExpression();
                }
                
                ExpressionType? op = null;
                if (left.NotEmpty)
                {
                    if (parser.TryConsume('?'))
                    {
                        var truePart = ParseTillTerminator(ref parser, ":",
                            false, true, out _);
                        // pass through the current parsing rules to consume the rest
                        var falsePart = ParseTillTerminator(ref parser, terminatorChars, throwOnTerminator, throwOnEnd,
                            out token);
                        
                        return new ConditionalExpression(left.ToExpression(), truePart, falsePart);
                    }
                    
                    // We expect a binary operator here

View on GitHub (pinned to 11c5427268)

Solutions

1. Complete the expression: an operand or closing delimiter is missing at the end of the string.
2. Ensure balanced parentheses and that every binary operator is followed by a value or identifier.

When it happens

Trigger: Raised when a composition expression ends before the parser expects it to (e.g. after an operator or open parenthesis). Defend by ensuring expressions are complete and balanced before passing them to ExpressionAnimation.

Common situations: See trigger scenarios.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/d3b516bec1c62246. Report an issue: GitHub.