dotnet/wpf · error · ArgumentException

SR.InvalidEmptyStrokeCollection

Error message

SR.InvalidEmptyStrokeCollection

What it means

InkCanvasGestureEventArgs requires the strokes parameter to contain at least one Stroke. An empty StrokeCollection fails the strokes.Count < 1 guard and throws ArgumentException (SR.InvalidEmptyStrokeCollection) because a gesture event with no ink is meaningless for recognition.

Solutions

1. Check strokes.Count > 0 before constructing the event args and skip raising the gesture event when empty.
2. Erase strokes only after gesture processing completes, not before constructing the args.
3. In the Gesture handler, guard with if (e == null || strokeSource.Count == 0) return; when synthesizing args yourself.

Example fix

// before
var args = new InkCanvasGestureEventArgs(collectedStrokes, results);
RaiseEvent(args);

// after
if (collectedStrokes.Count > 0)
{
    var args = new InkCanvasGestureEventArgs(collectedStrokes, results);
    RaiseEvent(args);
}

if (strokes == null || strokes.Count < 1)
    return; // skip gesture event
var args = new InkCanvasGestureEventArgs(strokes, results);

bool HasStrokes(StrokeCollection sc) => sc is { Count: > 0 };

try { var args = new InkCanvasGestureEventArgs(strokes, results); RaiseEvent(args); }
catch (ArgumentException ex) when (ex.ParamName == "strokes")
{ /* no ink captured; skip gesture processing */ }

When it happens

Trigger: new InkCanvasGestureEventArgs(new StrokeCollection(), results) or passing a collection whose strokes were all removed/erased before the gesture event args were built.

Common situations: Custom gesture handling where the user's stroke was deleted between capture and arg construction; programmatically raising the Gesture event with no ink; replay/test harnesses building args from empty input buffers.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• SR.InvalidEmptyArray
• SR.EmptyArrayNotAllowedAsArgument
• Can only countersign parts with Digital Signature…
• Duplicates not allowed - signature part already exists.
• ExtendedProperty is already part of the…

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/7d5650b239a17073. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Ink/Events.cs:305

    /// </summary>
    public class InkCanvasGestureEventArgs : RoutedEventArgs
    {
        private StrokeCollection _strokes;
        private List<GestureRecognitionResult> _gestureRecognitionResults;
        private bool                _cancel;

        /// <summary>
        /// TBD
        /// </summary>
        /// <param name="strokes">strokes</param>
        /// <param name="gestureRecognitionResults">gestureRecognitionResults</param>
        public InkCanvasGestureEventArgs(StrokeCollection strokes, IEnumerable<GestureRecognitionResult> gestureRecognitionResults)
            : base(InkCanvas.GestureEvent)
        {
            ArgumentNullException.ThrowIfNull(strokes);
            if (strokes.Count < 1)
            {
                throw new ArgumentException(SR.InvalidEmptyStrokeCollection, nameof(strokes));
            }
            ArgumentNullException.ThrowIfNull(gestureRecognitionResults);
            List<GestureRecognitionResult> results = 
                new List<GestureRecognitionResult>(gestureRecognitionResults);
            if (results.Count == 0)
            {
                throw new ArgumentException(SR.InvalidEmptyArray, nameof(gestureRecognitionResults));
            }
            _strokes = strokes;
            _gestureRecognitionResults = results;
        }

        /// <summary>
        /// TBD
        /// </summary>
        public StrokeCollection Strokes
        {
            get { return _strokes; }

View on GitHub (pinned to 81131a70a4)