Regarding to the C# code

<title>CasCading Dropdowns Sampletitle>

head>

<body>

<div>

<tr>

<td>

Select Country:

td>

<td>

<asp:DropDownList ID="ddlCountry" runat="server" AutoPostBack="true"

onselectedindexchanged="ddlCountry_SelectedIndexChanged">asp:DropDownList>

td>

tr>

<tr>

<td>

Select State:

td>

<td>

<asp:DropDownList ID="ddlState" runat="server" AutoPostBack="true"

onselectedindexchanged="ddlState_SelectedIndexChanged">asp:DropDownList>

td>

tr>

<tr>

<td>

Select Region:

td>

<td>

<asp:DropDownList ID="ddlRegion" runat="server">asp:DropDownList>

td>

tr>

table>

div>

form>

body>

html>

In code behind write like this

private String strConnection = "Data Source=XZCBJ017550;Initial Catalog=MySamplesDB;Integrated Security=True";

protected void Page_Load(object sender, EventArgs e)

{

if(!IsPostBack)

{

BindContrydropdown();

}

///

/// Bind COuntrydropdown

///

protected void BindContrydropdown()

{

//conenction path for database

SqlConnection con = new SqlConnection(strConnection);

con.Open();

SqlCommand cmd = new SqlCommand("select * from CountryTable", con);

SqlDataAdapter da = new SqlDataAdapter(cmd);

DataSet ds = new DataSet();

da.Fill(ds);

con.Close();

ddlCountry.DataSource = ds;

ddlCountry.DataTextField = "CountryName";

ddlCountry.DataValueField = "CountryID";

ddlCountry.DataBind();

ddlCountry.Items.Insert(0, new ListItem("--Select--", "0"));

ddlState.Items.Insert(0, new ListItem("--Select--", "0"));

ddlRegion.Items.Insert(0, new ListItem("--Select--", "0"));

}

///

/// Bind State Dropdown Based on CountryID

///

protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e)

{

int CountryID = Convert.ToInt32(ddlCountry.SelectedValue);

SqlConnection con = new SqlConnection(strConnection);

con.Open();

SqlCommand cmd = new SqlCommand("select * from StateTable where CountryID="+CountryID, con);

SqlDataAdapter da = new SqlDataAdapter(cmd);

DataSet ds = new DataSet();

da.Fill(ds);

con.Close();

ddlState.DataSource = ds;

ddlState.DataTextField = "StateName";

ddlState.DataValueField = "StateID";

ddlState.DataBind();

ddlState.Items.Insert(0, new ListItem("--Select--", "0"));

if(ddlState.SelectedValue=="0")

{

ddlRegion.Items.Clear();

ddlRegion.Items.Insert(0, new ListItem("--Select--", "0"));

}

///

/// Bind Region dropdown based on Re

///

protected void ddlState_SelectedIndexChanged(object sender, EventArgs e)

{

int StateID = Convert.ToInt32(ddlState.SelectedValue);

SqlConnection con = new SqlConnection(strConnection);

con.Open();

SqlCommand cmd = new SqlCommand("select * from RegionTable where StateID=" + StateID, con);

SqlDataAdapter da = new SqlDataAdapter(cmd);

DataSet ds = new DataSet();

da.Fill(ds);

con.Close();

ddlRegion.DataSource = ds;

ddlRegion.DataTextField = "RegionName";

ddlRegion.DataValueField = "RegionID";

ddlRegion.DataBind();

ddlRegion.Items.Insert(0, new ListItem("--Select--", "0"));

}