Json.net deserialize interface, concrete class uses a JsonConverter - interface

Question

My problem is that my JsonConverter doesn't seem to get invoked by the json.net de-serialization process when the converter is applied to an implementation of an interface, and the propertytype is the interface.
I use TypeNameHandling = TypeNameHandling.Objects to add $type to the json. I do so both on serialization and on de-serialization.
And when I have a property that is of an implementation of the interface the class' converter is invoked properly.
But when I have a property of interface type, the concrete class' converter is not invoked.
When I deserialize this class my JsonDataBagCreationConverter will be invoked by the RealTelephone but not by the Telephone because this is an interface.
Even though they are both serialized with the correct $type.
This results in RealTelephone having its .Data filled whereas Telephones .Data is null.
[JsonConverter(typeof(JsonDataBagCreationConverter<ContainerForITelephone>))]
public class ContainerForITelephone : IDataBag
{
private object _data;
private DataBagTypeEnum _dataBagTypeEnum;
public ITelephone Telephone { get; set; }
public Telephone RealTelephone { get; set; }
public object Data
{
get { return _data; }
set { _data = value; }
}
public DataBagTypeEnum DataBagType_Enum
{
get { return _dataBagTypeEnum; }
}
}
This jsonconverter is not invoked for the Telephone property. But it is for RealTelephone.
public class JsonDataBagCreationConverter<T> : JsonConverter where T : IDataBag, new()
{
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (reader.TokenType != JsonToken.Null)
{
var jsonObject = JObject.Load(reader);
var target = Create(objectType, jsonObject);
serializer.Populate(jsonObject.CreateReader(), target);
((IDataBag)target).Data = jsonObject.ToString();
return target;
}
return null;
}
}
[JsonConverter(typeof(JsonDataBagCreationConverter<Telephone>))]
public class Telephone : ITelephone
{
public string Name { get; set; }
public string AreaCode { get; set; }
public string Number { get; set; }
public SubPhone SubPhone { get; set; }
public object Data { get; set; }
public DataBagTypeEnum DataBagType_Enum { get; set; }
}
I look forward to hearing from you, thanks
Jan

Answer 1

SOLVED:
public class JsonDataBagCreationConverter<T> : JsonConverter where T:IDataBag
{
//, new() prevented us from using interfaces. Activator.CreateInstance did the trick in Create
//Used when the object decorated with [JsonConverter(typeof(JsonDataBagCreationConverter<xxxx>))] is de-serialized
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
var jsonObject = JObject.Load(reader);
if (objectType.IsInterface)
{
// Interfaces cannot be instantiated but must be converted to their "real" implemented type
// Because we serialize with settings.TypeNameHandling = TypeNameHandling.Objects;
// A $type property is added to the json by the deserializer.
string type = jsonObject["$type"].ToString();
var typesAsArray = type.Split(',');
var wrappedTarget = Activator.CreateInstance(typesAsArray[1], typesAsArray[0]);
var realTarget = wrappedTarget.Unwrap() as IDataBag;
serializer.Populate(jsonObject.CreateReader(), realTarget); // Will call this function recursively for any objects that have JsonDataBagCreationConverter as attribute
((IDataBag)realTarget).Data = jsonObject.ToString(); // This is where custom data is stored in databag
return realTarget;
}
// Non interface
var target = Create(objectType, jsonObject);
serializer.Populate(jsonObject.CreateReader(), target); // Will call this function recursively for any objects that have JsonDataBagCreationConverter as attribute
((IDataBag)target).Data = jsonObject.ToString(); // This is where custom data is stored in databag
return target;
}
public override bool CanRead
{
get
{
return true;
}
}
public override bool CanWrite
{
get
{
return false;
}
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new Exception("WriteJson not implemented");
}
protected IDataBag Create(Type objectType, JObject jsonObject)
{
var aa = Activator.CreateInstance(objectType);
return aa as IDataBag;
// return new T(); // this demands ,new() on the class and then it will not work with interfaces
}
public override bool CanConvert(Type objectType)
{
return typeof(T).IsAssignableFrom(objectType);
}
}