C# JSON custom serialization

Solution 1:

First i suggest to use newton json dll.

Second your need create custom JsonConverter for KeyValuePair like this:

  public class PairConverter : JsonConverter
  {
    public override bool CanConvert(Type objectType)
    {
       return objectType == typeof(KeyValuePair<string, int>);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
      throw new NotImplementedException();
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
      var item = (KeyValuePair<string, int>)value;
      writer.WriteValue(item.Value);
      writer.Flush();
    }
  }

And than add JsonConverter attribute for 'Age' property like this:

 public class Persons
 {
   [JsonConverter(typeof(PairConverter))]
   public KeyValuePair<string, int> Age { get; set; }
 }

Finally, example of usage:

 var persons = new Persons()
 {
    Age = new KeyValuePair<string, int>("Age", 10)
 };
 var json = JsonConvert.SerializeObject(persons); // {Age:10}