Illustrating Factory pattern with a very basic example

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using FactoryClass;
using ChoiceInterface;

namespace DesignPatterns
{
    public partial class ClientForm : Form
    {
        public ClientForm()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            IChoice objInvoice;
            objInvoice = FactoryClass.FactoryChoice.getChoiceObj(txtChoice.Text.Trim());
             MessageBox.Show(objInvoice.Buy());
        }
    }
}