dotnet/wpf · error · ArgumentException

SR.Animation_KeySpline_InvalidValue (ControlPoint1)

Error message

SR.Animation_KeySpline_InvalidValue (ControlPoint1)

What it means

The KeySpline.ControlPoint1 property setter throws ArgumentException (SR.Animation_KeySpline_InvalidValue) when assigning a point whose X or Y is outside the required [0,1] range. The setter only validates when the new value differs from the current one, but any genuinely out-of-range assignment fails.

Solutions

Clamp the point before assignment: new Point(Math.Clamp(x,0,1), Math.Clamp(y,0,1)).
Constrain UI inputs (sliders min=0 max=1) or normalize parsed values by dividing by their max.
Wrap the setter in try/catch (ArgumentException) and keep/restore the previous control point.
If the spline is replaceable, construct a new KeySpline with validated points instead of mutating.

Example fix

// before
spline.ControlPoint1 = new Point(userX, userY);
// after
spline.ControlPoint1 = new Point(Math.Clamp(userX, 0, 1), Math.Clamp(userY, 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.ControlPoint1 = value;

Type guard

static Point SafeControlPoint1(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.ControlPoint1;
try { spline.ControlPoint1 = candidate; }
catch (ArgumentException) { spline.ControlPoint1 = previous; }

Prevention

Bind spline editors to sliders with Minimum=0, Maximum=1
Clamp computed/animated control points before assignment
Validate values parsed from XAML/config for range, not just type
Never assign raw external easing data without normalization

When it happens

Trigger: keySpline.ControlPoint1 = new Point(x, y) where x < 0, x > 1, y < 0 or y > 1; also storyboard/key-frame code paths that assign control points computed at runtime.

Common situations: Animating spline control points driven by sliders or parsed input without range constraints; config systems storing 0-100 percent values; cumulative arithmetic drift pushing coordinates slightly above 1.

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/4ac18ffcd52ffe29. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/KeySpline.cs:167

        /// 
        /// </summary>
        public Point ControlPoint1
        {
            get
            {
                ReadPreamble();

                return _controlPoint1;
            }
            set
            {
                WritePreamble();

                if (value != _controlPoint1)
                {
                    if (!IsValidControlPoint(value))
                    {
                        throw new ArgumentException(SR.Format(
                            SR.Animation_KeySpline_InvalidValue,
                            "ControlPoint1",
                            value));
                    }

                    _controlPoint1 = value;

                    WritePostscript();
                }
            }
        }

        /// <summary>
        /// 
        /// </summary>
        public Point ControlPoint2
        {
            get

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