Create Json dynamically in c#

[TestFixture]
public class DynamicJson
{
    [Test]
    public void Test()
    {
        dynamic flexible = new ExpandoObject();
        flexible.Int = 3;
        flexible.String = "hi";

        var dictionary = (IDictionary<string, object>)flexible;
        dictionary.Add("Bool", false);

        var serialized = JsonConvert.SerializeObject(dictionary); // {"Int":3,"String":"hi","Bool":false}
    }
}

I found a solution very similar to DPeden, though there is no need to use the IDictionary, you can pass directly from an ExpandoObject to a JSON convert:

dynamic foo = new ExpandoObject();
foo.Bar = "something";
foo.Test = true;
string json = Newtonsoft.Json.JsonConvert.SerializeObject(foo);

and the output becomes:

{ "FirstName":"John", "LastName":"Doe", "Active":true }

You should use the JavaScriptSerializer. That can Serialize actual types for you into JSON :)

Reference: http://msdn.microsoft.com/en-us/library/system.web.script.serialization.javascriptserializer.aspx

EDIT: Something like this?

var columns = new Dictionary<string, string>
            {
                { "FirstName", "Mathew"},
                { "Surname", "Thompson"},
                { "Gender", "Male"},
                { "SerializeMe", "GoOnThen"}
            };

var jsSerializer = new JavaScriptSerializer();

var serialized = jsSerializer.Serialize(columns);

Output:

{"FirstName":"Mathew","Surname":"Thompson","Gender":"Male","SerializeMe":"GoOnThen"}