dotnet/wpf · error · ArgumentException

SR.Animation_KeySpline_InvalidValue (ControlPoint2)

Error message

SR.Animation_KeySpline_InvalidValue (ControlPoint2)

What it means

The KeySpline.ControlPoint2 property setter throws ArgumentException (SR.Animation_KeySpline_InvalidValue) when the assigned point has any X or Y coordinate outside [0,1]. Like ControlPoint1, the value is only written after IsValidControlPoint passes, keeping the timing curve inside the unit square.

Solutions

Clamp both coordinates into [0,1] before setting ControlPoint2.
Validate in the input layer (slider ranges, numeric updown min/max) so out-of-range values never reach the setter.
Catch ArgumentException around the assignment and revert to the previous value.
Recreate the KeySpline via the constructor with both points validated together.

Example fix

// before
spline.ControlPoint2 = parsedPoint;
// after
spline.ControlPoint2 = new Point(Math.Clamp(parsedPoint.X, 0, 1), Math.Clamp(parsedPoint.Y, 0, 1));

Defensive patterns

Strategy: validation

Validate before calling

if (value.X < 0 || value.X > 1 || value.Y < 0 || value.Y > 1)
    value = new Point(Math.Clamp(value.X, 0, 1), Math.Clamp(value.Y, 0, 1));
spline.ControlPoint2 = value;

Type guard

static Point SafeControlPoint2(Point p) => new Point(Math.Clamp(p.X, 0.0, 1.0), Math.Clamp(p.Y, 0.0, 1.0));

Try / catch

Point previous = spline.ControlPoint2;
try { spline.ControlPoint2 = candidate; }
catch (ArgumentException) { spline.ControlPoint2 = previous; }

Prevention

Apply the same [0,1] clamp helper to both control points
Check imported cubic-bezier data: some formats allow x outside [0,1]
Constrain UI numeric inputs before they reach the setter
Prefer recreating the KeySpline with validated points over in-place mutation

When it happens

Trigger: keySpline.ControlPoint2 = new Point(x, y) with x or y < 0.0 or > 1.0, e.g. from an easing editor or generated animation code.

Common situations: Easing-curve editors without input clamping; importing spline data from formats allowing overshoot (e.g. raw CSS cubic-bezier x-values outside [0,1]); percentage-based configuration.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/7380f1461468bc96. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/KeySpline.cs:199

        /// 
        /// </summary>
        public Point ControlPoint2
        {
            get
            {
                ReadPreamble();

                return _controlPoint2;
            }
            set
            {
                WritePreamble();

                if (value != _controlPoint2)
                {
                    if (!IsValidControlPoint(value))
                    {
                        throw new ArgumentException(SR.Format(
                            SR.Animation_KeySpline_InvalidValue,
                            "ControlPoint2",
                            value));
                    }

                    _controlPoint2 = value;

                    WritePostscript();
                }
            }
        }

        /// <summary>
        /// Calculates spline progress from a linear progress.
        /// </summary>
        /// <param name="linearProgress">the linear progress</param>
        /// <returns>the spline progress</returns>
        public double GetSplineProgress(double linearProgress)

View on GitHub (pinned to 81131a70a4)