Example of generic and extension method in C#

namespace GenericSample

{

    public class DropdownListItem

    {

        public string Description { get; set; }

        public int Value { get; set; }

    }

    public class User

    {

        public int UserID { get; set; }

        public string UserName { get; set; }

    }

    public class Role

    {

        public int RoleID { get; set; }

        public string RoleName { get; set; }

    }

    class Program

    {

        static void Main(string[] args)

        {

            List<User> users = new List<User>();

            users.Add(new User() { UserID = 1, UserName = "Hemant" });

            users.Add(new User() { UserID = 2, UserName = "Vijay" });

            List<Role> roles = new List<Role>();

            roles.Add(new Role() { RoleID = 1, RoleName = "Admin" });

            roles.Add(new Role() { RoleID = 2, RoleName = "Manager" });

            List<DropdownListItem> ddlUsers = users.ToSelectList<User>(u => u.UserName, u => u.UserID).ToList();

            Console.WriteLine("User Details:-");

            foreach (DropdownListItem ddl in ddlUsers)

            {

                Console.WriteLine("UserID: {0}, UserName : {1}", ddl.Value, ddl.Description);

            }

           

            List<DropdownListItem> ddlRoles = roles.ToSelectList<Role>(u => u.RoleName, u => u.RoleID).ToList();

            Console.WriteLine("Role Details:-");

            foreach (DropdownListItem ddl in ddlRoles)

            {

                Console.WriteLine("RoleID: {0}, RoleName : {1}", ddl.Value, ddl.Description);

            }

            Console.ReadLine();

        }

    }

    static class GenticClass

    {

        // Generic extension method to convert a type into DropDownItem

        public static List<DropdownListItem> ToSelectList<T>(this List<T> glist, Func<T, string> text, Func<T, int> value)

        {

            List<DropdownListItem> ddlList = new List<DropdownListItem>();

            glist.ForEach(x =>

            {

                ddlList.Add(new DropdownListItem() { Value = value(x), Description = text(x) });

            });

            return ddlList;

        }

    }

}