Asp.net textbox validate event

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="WebApplication2._Default" %>





   
   


   

   

   
   
       

                Text="Please enter any ShoseCode to be verified from the database"
            runat="server" BackColor="#FFFF99"
        Width="197px" ForeColor="#FF3300">
                    AutoPostBack="True" ontextchanged="txt_ShoseCode_TextChanged">
   
            ControlToValidate="txt_ShoseCode" ErrorMessage="*ShoseCode Required">
   
   

   
              
                         ForeColor="Black">
       
   

   

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;
namespace WebApplication2
{
    public partial class _Default : System.Web.UI.Page
    {
        string connStr = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        SqlCommand com;
        string str ;

     
        public void ShoseCode_check()
        {
            SqlConnection con = new SqlConnection(connStr);
            con.Open();
            str = "select count(*)from Shose where ShoseCode ='" + txt_ShoseCode.Text + "'";
            com = new SqlCommand(str, con);
            int count = Convert.ToInt32(com.ExecuteScalar());
            if (count > 0)
            {
             
                ScriptManager.RegisterStartupScript(this, this.GetType(), "ShowSuccess", "javascript:Display('" + txt_ShoseCode.Text + "')", true);
                lblMessage.Text = "This Shoes Code already exist";
            }
            else
            {
              
                ScriptManager.RegisterStartupScript(this, this.GetType(), "ShowSuccess", "javascript:Display('" + txt_ShoseCode.Text + "')", true);
                lblMessage.Text = "This Shoes Code does not exist";
            }

        }

        protected void txt_ShoseCode_TextChanged(object sender, EventArgs e)
        {
            ShoseCode_check();
        }

        protected void Timer1_Tick(object sender, EventArgs e)
        {
            Label1.Text = DateTime.Now.ToString();
        }
    }
}