AvaloniaUI/Avalonia · error · ArgumentException

Invalid variant type: {typeof(T)}

Error message

Invalid variant type: {typeof(T)}

What it means

Error "Invalid variant type: {typeof(T)}" thrown in AvaloniaUI/Avalonia.

Source

Thrown at src/Avalonia.Base/Rendering/Composition/Expressions/ExpressionVariant.cs:848

            => default(T) switch
            {
                bool => (bool)(object)v,
                float => (float)(object)v,
                double => (double)(object)v,
                System.Numerics.Vector2 => (Vector2)(object)v,
                Avalonia.Vector => (Vector)(object)v,
                System.Numerics.Vector3 => (Vector3)(object)v,
                Avalonia.Vector3D => (Vector3D)(object)v,
                System.Numerics.Vector4 => (Vector4)(object)v,
                System.Numerics.Matrix3x2 => (Matrix3x2)(object)v,
                Avalonia.Matrix => (Matrix)(object)v,
                System.Numerics.Matrix4x4 => (Matrix4x4)(object)v,
                System.Numerics.Quaternion => (Quaternion)(object)v,
                Avalonia.Media.Color => (Avalonia.Media.Color)(object)v,
                Avalonia.RelativePoint => (RelativePoint)(object)v,
                Avalonia.RelativeScalar => (RelativeScalar)(object)v,
                Avalonia.RelativeUnit => (RelativeUnit)(object)v,
                _ => throw new ArgumentException("Invalid variant type: " + typeof(T))
            };

        public T CastOrDefault<T>() where T : struct
        {
            TryCast<T>(out var r);
            return r;
        }

        public override string ToString()
        {
            return Type switch
            {
                VariantType.Boolean => Boolean.ToString(),
                VariantType.Double => Double.ToString(CultureInfo.InvariantCulture),
                VariantType.Vector2 => Vector2.ToString(),
                VariantType.Vector => Vector.ToString(),
                VariantType.Vector3 => Vector3.ToString(),
                VariantType.Vector3D => Vector3D.ToString(),

View on GitHub (pinned to 11c5427268)

Solutions

1. Use a supported ExpressionVariant type (e.g. float, Vector2, Vector3, Vector4, Color, bool, string) for the expression value.
2. Convert the value to a supported scalar or vector type before assigning it to the variant.

When it happens

Trigger: Raised when code attempts to read or set an ExpressionVariant with a type that has no defined variant representation. Defend by only using supported variant types (scalars, vectors, matrices, strings, booleans, colors) in expression values.

Common situations: See trigger scenarios.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/93408f2c7964c138. Report an issue: GitHub.