Recursively call JsonSerializer in a JsonConverter

Question

I\'m writing a JsonConverter to perform some conversion tasks I need accomplished on read/write. In particular, I\'m taking the existing serialization behavior

Answer 1

This is a very common problem. Using "JsonConvert.SerializeObject" isn't a bad idea. However, one trick that can be used in some circumstances (typically collections) is to cast to the interface when writing and deserialize to a simple derivative when reading.

Below is a simple converter that deals with dictionaries that might have been serialized as a set of KVPs rather than looking like an object (showing my age here :) )

Note "WriteJson" casts to IDictionary< K,V> and "ReadJson" uses "DummyDictionary". You end up with the right thing but uses the passed serializer without causing recursion.

/// 

/// Converts a  to and from JSON.
/// 
public class DictionaryAsKVPConverter : JsonConverter
{
    /// 

    /// Determines whether this instance can convert the specified object type.
    /// 
    /// Type of the object.
    /// 
    ///     true if this instance can convert the specified object type; otherwise, false.
    /// 
    public override bool CanConvert(Type objectType)
    {
        if (!objectType.IsValueType && objectType.IsGenericType)
            return (objectType.GetGenericTypeDefinition() == typeof(Dictionary<,>));

        return false;
    }

    /// 

    /// Writes the JSON representation of the object.
    /// 
    /// The  to write to.
    /// The value.
    /// The calling serializer.
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var dictionary = value as IDictionary;
        serializer.Serialize(writer, dictionary);
    }

    /// 

    /// Reads the JSON representation of the object.
    /// 
    /// The  to read from.
    /// Type of the object.
    /// The existing value of object being read.
    /// The calling serializer.
    /// The object value.
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        Dictionary dictionary;

        if (reader.TokenType == JsonToken.StartArray)
        {
            dictionary = new Dictionary();
            reader.Read();
            while (reader.TokenType == JsonToken.StartObject)
            {
                var kvp = serializer.Deserialize>(reader);
                dictionary[kvp.Key] = kvp.Value;
                reader.Read();
            }
        }
        else if (reader.TokenType == JsonToken.StartObject)
            // Use DummyDictionary to fool JsonSerializer into not using this converter recursively
            dictionary = serializer.Deserialize(reader);
        else
            dictionary = new Dictionary();

        return dictionary;
    }

    /// 

    /// Dummy to fool JsonSerializer into not using this converter recursively
    /// 
    private class DummyDictionary : Dictionary { }
}