JSON.NET Serialization of NameValueCollection

Yesterday, a colleague of mine was having problems implementing a Web API microservice, where client was throwing the exception:

'Cannot create and populate list type System.Collections.Specialized.NameValueCollection. Path ...' on de-serialization of a complex graph containing NameValueCollections.

Web searches returned a number suggestions to replace the NameValueCollection with a dictionary, which did not work in our case, where we needed to use classes as is.

As I've created the initial reference architecture, I felt obliged to help resolve the issue. As said, Web searches for a solution didn't return anything closely applicable, I've taken a bit deeper look at the Json.NET library documentation, and shortly afterwards decided to create a custom converter.

It turned out to be easy. Here's the source code:

/// <summary>
/// Custom converter for (de)serializing NameValueCollection
/// Add an instance to the settings Converters collection
/// </summary>
public class NameValueCollectionConverter : JsonConverter
{
  public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
  {
    var collection = value as NameValueCollection;
    if (collection == null)
      return;

    writer.WriteStartObject();
    foreach (var key in collection.AllKeys)
    {
      writer.WritePropertyName(key);
      writer.WriteValue(collection.Get(key));
    }
    writer.WriteEndObject();
  }

  public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
  {
    var nameValueCollection = new NameValueCollection();
    var key = "";
    while (reader.Read())
    {
      if (reader.TokenType == JsonToken.StartObject)
      {
        nameValueCollection = new NameValueCollection();
      }
      if (reader.TokenType == JsonToken.EndObject)
      {
        return nameValueCollection;                    
      }
      if (reader.TokenType == JsonToken.PropertyName)
      {
        key = reader.Value.ToString();
      }
      if (reader.TokenType == JsonToken.String)
      {
        nameValueCollection.Add(key, reader.Value.ToString());
      }
    }
    return nameValueCollection;
  }

  public override bool CanConvert(Type objectType)
  {
    return objectType == typeof(NameValueCollection);
  }
}

To user the converter, add it to the converters collection as follows:

var settings = new JsonSerializerSettings()
  {
    ContractResolver = new CamelCasePropertyNamesContractResolver(),
    TypeNameHandling = TypeNameHandling.All,
    Formatting = Formatting.Indented
  };
  settings.Converters.Add(new NameValueCollectionConverter());
  JsonConvert.DefaultSettings = () => settings;

Nice job done in implementing and documenting Json.NET!