Serializing KeyValuePair<TKey, TValue> type property to JSON in C#

Question

I'm trying to serialize a KeyValuePair property in C# that looks like this:

[JsonDisplayName("custom")]
public  KeyValuePair<string,string> Custom { get; set; }

to JSON by setting the property with:

MyClass.Custom = new KeyValuePair<string, string>("destination", destination);

But the output I get looks something like this:

"custom":{"Key":"destination","Value":"Paris"}

Instead I want:

"custom":{"destination":"Paris"}

Any ideas how? I'm using Compact Framework and Visual Studio 2008 so I prefer not to use any external library. You're help is greatly appreciated.

Update: I have to use my company's Model class which has a SetCustom method that throws an exception if I use a dictionary.

Answer 1

You can use dictionary instead of key value pair

public class A
{
    [JsonProperty("custom")]
    public Dictionary<string, string> Custom
    {
        get;
        set;
    }
}
public class Program
{
    public static void Main()
    {
        A custom = new A();
        custom.Custom = new Dictionary<string, string>(){
            {"destination1", "foo"},
            {"destination2", "bar"},
        };
        Console.WriteLine(JsonConvert.SerializeObject(custom));
    }
}

This will produce

{"custom":{"destination1":"foo","destination2":"bar"}}

Or if you want to stick with KeyValuePair you will need to create your own converter

public class A
{
    [JsonProperty("custom")]
    public KeyValuePair<string, string> Custom
    {
        get;
        set;
    }
}

class KeyValueStringPairConverter : JsonConverter
{
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        KeyValuePair<string, string> item = (KeyValuePair<string, string>)value;
        writer.WriteStartObject();
        writer.WritePropertyName(item.Key);
        writer.WriteValue(item.Value);
        writer.WriteEndObject();
    }

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

    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof (KeyValuePair<string, string>);
    }
}

public class Program
{
    public static void Main()
    {
        A custom = new A();
        JsonSerializerSettings settings = new JsonSerializerSettings{Converters = new[]{new KeyValueStringPairConverter()}};
        custom.Custom = new KeyValuePair<string, string>("destination", "foo");
        Console.WriteLine(JsonConvert.SerializeObject(custom, settings));
    }
}