dotnet/wpf · error · ArgumentException

SR.Format(SR.InvalidCtorParameterUnknownGridUnitType…

Error message

SR.Format(SR.InvalidCtorParameterUnknownGridUnitType, "type")

What it means

GridLength's constructor only accepts GridUnitType.Auto, GridUnitType.Pixel, or GridUnitType.Star. Any other GridUnitType value (including undefined numeric casts) fails this guard and throws ArgumentException (SR.InvalidCtorParameterUnknownGridUnitType) because the unit type would have no meaning for layout.

Solutions

Validate the unit type before constructing: Enum.IsDefined(typeof(GridUnitType), type) and that it is one of Auto/Pixel/Star.
Map unknown values to a safe default (Pixel or Auto) at the deserialization boundary.
Persist GridUnitType as its named string rather than a raw integer.
Audit cast sites: replace (GridUnitType)intValue with an explicit switch that has a default fallback.

Example fix

// before
var length = new GridLength(value, (GridUnitType)storedInt);

// after
var type = storedInt is >= 0 and <= 2 ? (GridUnitType)storedInt : GridUnitType.Pixel;
var length = new GridLength(type == GridUnitType.Auto ? 0 : value, type);

Defensive patterns

Strategy: validation

Validate before calling

if (type is not (GridUnitType.Auto or GridUnitType.Pixel or GridUnitType.Star))
    type = GridUnitType.Pixel;
var length = new GridLength(value, type);

Type guard

bool IsValidGridUnitType(GridUnitType t) => t is GridUnitType.Auto or GridUnitType.Pixel or GridUnitType.Star;

Try / catch

try { len = new GridLength(value, type); }
catch (ArgumentException ex) when (ex.ParamName == "type")
{ len = new GridLength(value, GridUnitType.Pixel); }

Prevention

Persist GridUnitType as a string, not an int.
Never cast raw ints to GridUnitType without Enum.IsDefined.
Restrict UI inputs to the three valid unit types via a whitelist.

When it happens

Trigger: new GridLength(10, (GridUnitType)42), deserializing a persisted enum int that is not 0/1/2, or passing a GridUnitType member added/renamed in another assembly version.

Common situations: Round-tripping GridLength settings through config or XAML-adjacent serialization where the enum was stored as a raw int; interop with code that uses different grid-unit constants; enum arithmetic producing out-of-range values.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/089a8705b16b8dc8. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/GridLength.cs:102

        /// If <c>value</c> parameter is <c>double.NaN</c>
        /// or <c>value</c> parameter is <c>double.NegativeInfinity</c>
        /// or <c>value</c> parameter is <c>double.PositiveInfinity</c>.
        /// </exception>
        public GridLength(double value, GridUnitType type)
        {
            if (double.IsNaN(value))
            {
                throw new ArgumentException(SR.Format(SR.InvalidCtorParameterNoNaN, "value"));
            }
            if (double.IsInfinity(value))
            {
                throw new ArgumentException(SR.Format(SR.InvalidCtorParameterNoInfinity, "value"));
            }
            if (    type != GridUnitType.Auto
                &&  type != GridUnitType.Pixel
                &&  type != GridUnitType.Star   )
            {
                throw new ArgumentException(SR.Format(SR.InvalidCtorParameterUnknownGridUnitType, "type"));
            }

            _unitValue = (type == GridUnitType.Auto) ? 0.0 : value;
            _unitType = type;
        }

        #endregion Constructors

        //------------------------------------------------------
        //
        //  Public Methods
        //
        //------------------------------------------------------

        #region Public Methods 

        /// <summary>
        /// Overloaded operator, compares 2 GridLength's.

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