AJAX DropDownList using UpdatePanel in C# and ASP.NET

Simple ASP.NET AJAX DropDownList USING UpdatePanel In C# ASP.NET 2005

Replace all "(" with '<' and also ")" with '>"

You can download AJAX controls in asp.net or From AJAX CONTROLS . Ajax stands for Asynchronous Javascript And XML. Here am going to bind data form database using AJAX UpdatePanel, and Binding city state and country for respected DropDownList.
As usual u can bind country DropDownList

C# code for Country DropDownList

protected void Page_Load(object sender, EventArgs e)
{

  if (!IsPostBack)
  {
      SqlConnection con = new SqlConnection("Data Source=SERVER; Integrated Security=SSPI;persist security info=True;Initial Catalog=DBNAME;");
      SqlCommand cmd = new SqlCommand("SELECT CountryName,CountryId FROM CountryTable", con);
      DataTable dt = new DataTable();
      con.Open();
      SqlDataAdapter adptr = new SqlDataAdapter(cmd);
      adptr.Fill(dt);
      con.Close();
      if (dt.Rows.Count > 0)
      {
          ddlCountry.Items.Clear();
          ddlCountry.Items.Add("SELECT");
          foreach (DataRow drow in dt.Rows)
          {
              ListItem lst = new ListItem();
              lst.Value = drow[1].ToString();
              lst.Text = drow[0].ToString();
              ddlCountry.Items.Add(lst);
          }
      }
  }

}

protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e)
{
  if (ddlCountry.SelectedValue.ToString() != "SELECT")
  {
      SqlConnection con = new SqlConnection("Data Source=SERVER; Integrated Security=SSPI;persist security info=True;Initial Catalog=DBNAME;");
      SqlCommand cmd = new SqlCommand(string.Format("SELECT StateName,StateId FROM StateTable WHERE CountryId='{0}'", ddlCountry.SelectedValue.ToString()), con);
      DataTable dt = new DataTable();
      con.Open();
      SqlDataAdapter adptr = new SqlDataAdapter(cmd);
      adptr.Fill(dt);
      con.Close();
      if (dt.Rows.Count > 0)
      {
          ddlState.Items.Clear();
          ddlState.Items.Add("SELECT");
          foreach (DataRow drow in dt.Rows)
          {
              ListItem lst = new ListItem();
              lst.Value = drow[1].ToString();
              lst.Text = drow[0].ToString();
              ddlState.Items.Add(lst);
          }
      }
  }
}

HTML code

(asp:dropdownlist id="ddlCountry" runat="server" onselectedindexchanged="ddlCountry_SelectedIndexChanged" autopostback="True")(/asp:dropdownlist)
(br) (asp:updatepanel id="upnl" runat="server")(br) (contenttemplate)(br) (asp:dropdownlist id="ddlState" runat="server")(/asp:dropdownlist)(br) (/contenttemplate)(br) (triggers)(br) (asp:asyncpostbacktrigger controlid="ddlCountry")(br) (/asp:asyncpostbacktrigger)