AvaloniaUI/Avalonia · error · NotSupportedException

Invalid BindingValueType.

Error message

Invalid BindingValueType.

What it means

Thrown as NotSupportedException by BindingValue<T>.ToObject() when the Type field does not match any known BindingValueType case in its switch expression (the default/_ arm). BindingValueType is a [Flags] enum; an unrecognized or corrupted flag combination that doesn't equal any named member triggers the default arm.

Source

Thrown at src/Avalonia.Base/Data/BindingValue.cs:166

        /// appropriate.
        /// </summary>
        /// <returns>The untyped representation of the binding value.</returns>
        public object? ToUntyped()
        {
            return Type switch
            {
                BindingValueType.UnsetValue => AvaloniaProperty.UnsetValue,
                BindingValueType.DoNothing => BindingOperations.DoNothing,
                BindingValueType.Value => _value,
                BindingValueType.BindingError =>
                    new BindingNotification(Error!, BindingErrorType.Error),
                BindingValueType.BindingErrorWithFallback =>
                    new BindingNotification(Error!, BindingErrorType.Error, Value),
                BindingValueType.DataValidationError =>
                    new BindingNotification(Error!, BindingErrorType.DataValidationError),
                BindingValueType.DataValidationErrorWithFallback =>
                    new BindingNotification(Error!, BindingErrorType.DataValidationError, Value),
                _ => throw new NotSupportedException("Invalid BindingValueType."),
            };
        }

        /// <summary>
        /// Returns a new binding value with the specified value.
        /// </summary>
        /// <param name="value">The new value.</param>
        /// <returns>The new binding value.</returns>
        /// <exception cref="InvalidOperationException">
        /// The binding type is <see cref="BindingValueType.UnsetValue"/> or
        /// <see cref="BindingValueType.DoNothing"/>.
        /// </exception>
        public BindingValue<T> WithValue(T value)
        {
            if (Type == BindingValueType.DoNothing)
            {
                throw new InvalidOperationException("Cannot add value to DoNothing binding value.");
            }

View on GitHub (pinned to 11c5427268)

Solutions

1. Always construct BindingValue<T> via its static factory methods (e.g., BindingValue<T>.FromValue, FromError) rather than the constructor, so Type is always valid.
2. If you must construct directly, ensure Type is exactly one of the named BindingValueType members.
3. Validate the Type against known members before calling ToObject().

Example fix

// before
var bv = new BindingValue<T>((BindingValueType)999, value, null);
var o = bv.ToObject(); // throws
// after
var bv = BindingValue<T>.FromValue(value); // factory sets a valid Type

var known = bv.Type is BindingValueType.UnsetValue or BindingValueType.DoNothing
    or BindingValueType.Value or BindingValueType.BindingError
    or BindingValueType.BindingErrorWithFallback
    or BindingValueType.DataValidationError or BindingValueType.DataValidationErrorWithFallback;
if (known) var o = bv.ToObject();

static bool IsValidType(BindingValueType t) =>
    t is BindingValueType.UnsetValue or BindingValueType.DoNothing or BindingValueType.Value
    or BindingValueType.BindingError or BindingValueType.BindingErrorWithFallback
    or BindingValueType.DataValidationError or BindingValueType.DataValidationErrorWithFallback;

try { var o = bv.ToObject(); }
catch (NotSupportedException ex) when (ex.Message.Contains("Invalid BindingValueType"))
{ /* log:BindingValue constructed with invalid Type; use a factory method */ }

When it happens

Trigger: BindingValue<T> is constructed directly (bypassing the static factory methods) with a Type value that is not one of UnsetValue, DoNothing, Value, BindingError, BindingErrorWithFallback, DataValidationError, DataValidationErrorWithFallback. Also theoretically reachable if reflection/binary deserialization produces an invalid enum.

Common situations: Internal/advanced code manually constructing BindingValue<T> with an invalid Type. Deserialization corruption. Unreleased enum member not handled by the switch. This is a defensive guard; normal factory APIs never produce this.

Related errors

• BindingValue has no value.
• Cannot add value to DoNothing binding value.
• Object of type '{value?.GetType()}' cannot be converted to t
• Value must be less than 10.
• Give me 5 or more letter please :-)

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/79bafc500c64f71e. Report an issue: GitHub.