TypeConverter is ignored when reading a value that implements IConvertible

[ashmind]

Example code (https://dotnetfiddle.net/iGB2mc):

using System;
using System.ComponentModel;
using System.Globalization;
using Newtonsoft.Json;

public class Program {
    public static void Main() {
        var simple = JsonConvert.DeserializeObject<X>("\"Simple\"");    
        Console.WriteLine(simple.Value);
    }
}

[TypeConverter(typeof(XTypeConverter))]
public sealed class X : IConvertible {
    public X(string value) {
        Value = value;
    }

    public string Value { get; private set; }

    TypeCode IConvertible.GetTypeCode() { return TypeCode.Object; } 
    bool IConvertible.ToBoolean(IFormatProvider provider)  { return false; }    
    char IConvertible.ToChar(IFormatProvider provider)     { return '\0'; }
    sbyte IConvertible.ToSByte(IFormatProvider provider)   { return 0; }    
    byte IConvertible.ToByte(IFormatProvider provider)     { return 0; }    
    short IConvertible.ToInt16(IFormatProvider provider)   { return 0; }    
    ushort IConvertible.ToUInt16(IFormatProvider provider) { return 0; }
    int IConvertible.ToInt32(IFormatProvider provider)     { return 0; }    
    uint IConvertible.ToUInt32(IFormatProvider provider)   { return 0; }    
    long IConvertible.ToInt64(IFormatProvider provider)    { return 0; }    
    ulong IConvertible.ToUInt64(IFormatProvider provider)  { return 0; }    
    float IConvertible.ToSingle(IFormatProvider provider)  { return 0; }    
    double IConvertible.ToDouble(IFormatProvider provider) { return 0; }    
    decimal IConvertible.ToDecimal(IFormatProvider provider) { return 0;}   
    DateTime IConvertible.ToDateTime(IFormatProvider provider) { return DateTime.MinValue; }    
    string IConvertible.ToString(IFormatProvider provider) { return ""; }   
    object IConvertible.ToType(Type conversionType, IFormatProvider provider) { return null; }
}

public class XTypeConverter : TypeConverter {
    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType) {
        return sourceType == typeof(string);
    }

    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value) {
        var @string = value as string;
        if (@string != null)
            return new X(@string);

        throw new NotSupportedException();
    }
}

Produces

Newtonsoft.Json.JsonSerializationException: Error converting value "Simple" to type 'X'. Path '', line 1, position 8. ---> System.InvalidCastException: Invalid cast from 'System.String' to 'X'.
   at System.Convert.DefaultToType(IConvertible value, Type targetType, IFormatProvider provider)
   at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType)
   --- End of inner exception stack trace ---
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings)

However if I remove IConvertible from X, it works.

[ashmind]

It's even more interesting with IDictionary<X, object>, which produces:

Could not convert string 'Key' to dictionary key type 'X'. Create a TypeConverter to convert from the string to the key type object.

even though TypeConverter exists and works in absence of IConvertible.

[JamesNK]

By design. You will need to override with a JsonConverter.

[ashmind]

@JamesNK That's what I wanted to use, but JsonConverter is not applied to Dictionary keys -- even the message explicitly suggests TypeConverter.

[JamesNK]

You could write a JsonConverter for the dictionary. Or you could deserialize to different type and then create the dictionary after you deserialize.

[dennisdoomen]

This really sounds like a bug. I've observed the same problem. Everything works as expected until your target object implements IConvertible. Then your type converter will be completely ignored.

[claudiobottari]

Getting the same, I just add a custom object to my app that implements IConvertible and now I can't serialize/deserialize... Currently looking for a workaround, any idea?

[webwarrior06]

Try adding [JsonObject] attribute above the class implementing the IConvertible interface.

[dkattan]

Adding [JsonObject] fixed this for me.