Implement Observer Pattern in an Absolutely Easy Example

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

namespace EventAndDelegate
{
    public partial class Form2 : Form
    {
        private Subject objSub;
        Form3 frm;

        public Form2()
        {
            InitializeComponent();
            objSub = new Subject();
        }

        private void Form2_Load(object sender, EventArgs e)
        {

        }

        private void btnOpen_Click(object sender, EventArgs e)
        {
            frm = new Form3(objSub);
            frm.Show();
        }

        private void rdRed_CheckedChanged(object sender, EventArgs e)
        {
            if (rdRed.Checked)
            {
                objSub.UpdateClient("RED");
                lblText.ForeColor = Color.Red;                
            }
        }

        private void rdGreen_CheckedChanged(object sender, EventArgs e)
        {
            if (rdGreen.Checked)
            {
                objSub.UpdateClient("GREEN");
                lblText.ForeColor = Color.Green;
            }
        }

        private void rdBlue_CheckedChanged(object sender, EventArgs e)
        {
            if (rdBlue.Checked)
            {
                objSub.UpdateClient("BLUE");
                lblText.ForeColor = Color.Blue;
            }
        }
    }
}