How to create own dynamic type or dynamic object in C#?

Question

dynamic MyDynamic = new System.Dynamic.ExpandoObject();
MyDynamic.A = "A";
MyDynamic.B = "B";
MyDynamic.C = "C";
MyDynamic.Number = 12;
MyDynamic.MyMethod = new Func<int>(() => 
{ 
    return 55; 
});
Console.WriteLine(MyDynamic.MyMethod());

Read more about ExpandoObject class and for more samples: Represents an object whose members can be dynamically added and removed at run time.

I recently had a need to take this one step further, which was to make the property additions in the dynamic object, dynamic themselves, based on user defined entries. The examples here, and from Microsoft's ExpandoObject documentation, do not specifically address adding properties dynamically, but, can be surmised from how you enumerate and delete properties. Anyhow, I thought this might be helpful to someone. Here is an extremely simplified version of how to add truly dynamic properties to an ExpandoObject (ignoring keyword and other handling):

        // my pretend dataset
        List<string> fields = new List<string>();
        // my 'columns'
        fields.Add("this_thing");
        fields.Add("that_thing");
        fields.Add("the_other");

        dynamic exo = new System.Dynamic.ExpandoObject();

        foreach (string field in fields)
        {
            ((IDictionary<String, Object>)exo).Add(field, field + "_data");
        }

        // output - from Json.Net NuGet package
        textBox1.Text = Newtonsoft.Json.JsonConvert.SerializeObject(exo);

ExpandoObject is what are you looking for.

dynamic MyDynamic = new ExpandoObject(); // note, the type MUST be dynamic to use dynamic invoking.
MyDynamic.A = "A";
MyDynamic.B = "B";
MyDynamic.C = "C";
MyDynamic.TheAnswerToLifeTheUniverseAndEverything = 42;

dynamic myDynamic = new { PropertyOne = true, PropertyTwo = false};