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;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            myTextBox1.CheckPass = myTextBox1.Handle.ToInt32() * 2;
            String strText = myTextBox1.Text;
            myTextBox1.CheckPass = 0;
            MessageBox.Show(strText);
        }
    }

    public class MyTextBox : TextBox
    {
        private Int32 _CheckPass;

        public Int32 CheckPass
        {
            get
            {
                return _CheckPass;
            }
            set
            {
                _CheckPass = value;
            }
        }

        protected override void WndProc(ref Message m)
        {
            if (m.Msg == 0x000D)
            {
                if (CheckPass != m.HWnd.ToInt32() * 2)
                {
                    return;
                }
            }

            base.WndProc(ref m);
        }
    }
}