AvaloniaUI/Avalonia · error · ArgumentNullException

geometryContext

Error message

geometryContext

What it means

Thrown by the PathMarkupParser constructor when the IGeometryContext argument is null. The parser is a writer: it parses a path markup string and emits BeginFigure/LineTo/BezierTo/etc. calls into the supplied IGeometryContext, so it cannot operate without a valid sink.

Source

Thrown at src/Avalonia.Base/Media/PathMarkupParser.cs:47

                };

        private IGeometryContext? _geometryContext;
        private Point _currentPoint;
        private Point? _beginFigurePoint;
        private Point? _previousControlPoint;
        private bool _isOpen;
        private bool _isDisposed;

        /// <summary>
        /// Initializes a new instance of the <see cref="PathMarkupParser"/> class.
        /// </summary>
        /// <param name="geometryContext">The geometry context.</param>
        /// <exception cref="ArgumentNullException">geometryContext</exception>
        public PathMarkupParser(IGeometryContext geometryContext)
        {
            if (geometryContext == null)
            {
                throw new ArgumentNullException(nameof(geometryContext));
            }

            _geometryContext = geometryContext;
        }

        private enum Command
        {
            None,
            FillRule,
            Move,
            Line,
            HorizontalLine,
            VerticalLine,
            CubicBezierCurve,
            QuadraticBezierCurve,
            SmoothCubicBezierCurve,
            SmoothQuadraticBezierCurve,
            Arc,

View on GitHub (pinned to 11c5427268)

Solutions

1. Pass a non-null IGeometryContext, typically obtained via ((StreamGeometry)geometry).Open() or StreamGeometryContext from a PathGeometry.
2. Guard the call site: if (context is not null) { using var p = new PathMarkupParser(context); p.Parse(data); }
3. If the context comes from a factory/field, ensure it is assigned before parser construction and never set back to null.

Example fix

// before
var parser = new PathMarkupParser(null);
parser.Parse("M0,0 L10,10");

// after
var sg = new StreamGeometry();
using (var ctx = sg.Open())
using (var parser = new PathMarkupParser(ctx))
{
    parser.Parse("M0,0 L10,10");
}

if (geometryContext is null)
    throw new ArgumentNullException(nameof(geometryContext));
var parser = new PathMarkupParser(geometryContext);

static bool IsValidContext(IGeometryContext? c) => c is not null;

When it happens

Trigger: Constructing the parser with a null context: new PathMarkupParser(null). Also happens when the variable holding the context was never assigned (e.g. a field left null, or a StreamGeometry.Open() result captured before the geometry was opened).

Common situations: Passing an unopened or disposed StreamGeometry's context, or wiring PathMarkupParser against a field that is conditionally initialized and happened to be null on this code path. Common when refactoring geometry creation or sharing a context across parsers.

Related errors

• points
• dictionary
• items
• array
• collection

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/a2019f436439ba16. Report an issue: GitHub.