using System;

using Newtonsoft.Json;

public class Program

{

    public class TodoUserPref

    {

        public string someinfo { get; set; }

    }

​

    public class InvoiceUserPref

    {

        public int somenumber { get; set; }

    }

​

    public class GetDto

    {

        public TodoUserPref TodoPref { get; set; }

        public InvoiceUserPref InvoicePref { get; set; }

    }

    public static void Main()

    {

        var returnObject = new GetDto();

        string inputKey = "TodoPref";

        var propToChange = returnObject.GetType().GetProperty(inputKey);

​

        var type = Type.GetType(propToChange.PropertyType.ToString());

​

        var asd = JsonConvert.DeserializeObject("{someinfo:\"asd\"}", type);

        propToChange.SetValue(returnObject, asd );

        Console.WriteLine(returnObject.TodoPref.someinfo);

    }

}