dotnet/aspnetcore · error · InvalidOperationException

The type '{0}' does not have an associated TypeConverter tha

Error message

The type '{0}' does not have an associated TypeConverter that supports conversion to a string. Apply 'TypeConverterAttribute' to the type to register a converter.

What it means

Thrown by BindConverter's FormatterDelegateCache.MakeTypeConverterFormatter when a type used in @bind has no TypeConverter capable of converting it to a string. Blazor needs to render bound values into input elements; for non-primitive types it falls back to TypeDescriptor.GetConverter, and if that converter can't convert to string, this InvalidOperationException is thrown. The fix is to apply [TypeConverter] on the type registering a converter that supports ConvertTo(typeof(string)).

Source

Thrown at src/Components/Components/src/BindConverter.cs:1848

                {
                    builder.Append(", \"");
                    builder.Append(JsonEncodedText.Encode(elementFormatter(value[i], culture)?.ToString() ?? string.Empty).Value);
                    builder.Append('\"');
                }

                builder.Append(']');

                return builder.ToString();
            }
        }

        [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "We expect unknown underlying types are configured by application code to be retained.")]
        private static BindFormatter<T> MakeTypeConverterFormatter<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] T>()
        {
            var typeConverter = TypeDescriptor.GetConverter(typeof(T));
            if (typeConverter == null || !typeConverter.CanConvertTo(typeof(string)))
            {
                throw new InvalidOperationException(
                    $"The type '{typeof(T).FullName}' does not have an associated {typeof(TypeConverter).Name} that supports " +
                    $"conversion to a string. " +
                    $"Apply '{typeof(TypeConverterAttribute).Name}' to the type to register a converter.");
            }

            return FormatWithTypeConverter;

            string? FormatWithTypeConverter(T value, CultureInfo? culture)
            {
                // We intentionally close-over the TypeConverter to cache it. The TypeDescriptor infrastructure is slow.
                return typeConverter.ConvertToString(context: null, culture ?? CultureInfo.CurrentCulture, value);
            }
        }
    }

    internal static class ParserDelegateCache
    {
        private static readonly ConcurrentDictionary<Type, Delegate> _cache = new ConcurrentDictionary<Type, Delegate>();

View on GitHub (pinned to 294cab2f9b)

Solutions

1. Create a TypeConverter subclass that overrides CanConvertTo(typeof(string)) and ConvertTo for string.
2. Apply [TypeConverter(typeof(YourConverter))] to your custom type.
3. Alternatively, bind a primitive/string property and convert in get/set accessors or in a separate computed property.

Example fix

// before
public struct Money
{
    public decimal Amount;
    public string Currency;
}
@* @bind to Money throws *@

// after
[TypeConverter(typeof(MoneyConverter))]
public struct Money { public decimal Amount; public string Currency; }

public class MoneyConverter : TypeConverter
{
    public override bool CanConvertTo(ITypeDescriptorContext c, Type t)
        => t == typeof(string) || base.CanConvertTo(c, t);
    public override object ConvertTo(ITypeDescriptorContext c, CultureInfo c2, object v, Type t)
        => t == typeof(string) ? ((Money)v).Amount.ToString(c2) : base.ConvertTo(c, c2, v, t);
}

var converter = TypeDescriptor.GetConverter(typeof(T));
if (converter is null || !converter.CanConvertTo(typeof(string)))
    throw new InvalidOperationException($"{typeof(T)} has no string TypeConverter.");

static bool CanFormatAsString<T>()
{
    var converter = TypeDescriptor.GetConverter(typeof(T));
    return converter is not null && converter.CanConvertTo(typeof(string));
}

When it happens

Trigger: Using @bind on an <input> element bound to a property of a custom type that has no TypeConverter registered, and is not one of the built-in supported types (string, int, bool, DateTime, Guid, enums, arrays, etc.). The formatter lookup happens at BindConverter.cs:1843-1861.

Common situations: Binding a custom struct/record/class (e.g., a Money, EmailAddress, or custom Identifier type) to an input without registering a TypeConverter; using a third-party value type that doesn't ship a converter.

Related errors

• The type '{0}' does not have an associated TypeConverter tha
• There is no file with ID ${fileId}. The file list may have c
• Invalid sequence number or identifier '${sequenceOrIdentifie
• The options parameter is required.
• The event '${eventName}' is already registered.

AI-assisted analysis of dotnet/aspnetcore@294cab2f9b (2026-08-06). Data as JSON: /api/errors/1cc91aa6d428df9a. Report an issue: GitHub.