Bind A DropDownList With Another DropDownList In ASP.NET Web Forms

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Data.SqlClient;

using System.Configuration;

using System.Data;

namespace BindingDDL

{

public partial class WebForm1 : System.Web.UI.Page

{

string cs = ConfigurationManager.ConnectionStrings["dbcs"].ConnectionString;

protected void Page_Load(object sender, EventArgs e)

{

if (!IsPostBack)

{

BindCountryDDL();

}

void BindCountryDDL()

{

SqlConnection con = new SqlConnection(cs);

string query = "select * from country";

SqlDataAdapter sda = new SqlDataAdapter(query,con);

DataTable data = new DataTable();

sda.Fill(data);

CountryDropDownList.DataSource = data;

CountryDropDownList.DataTextField = "country_name";

CountryDropDownList.DataValueField = "country_id";

CountryDropDownList.DataBind();

ListItem selectItem = new ListItem("Select Country", "Select Country");

selectItem.Selected = true;

CountryDropDownList.Items.Insert(0,selectItem);

}

void BindCityDDL(int country_id)

{

SqlConnection con = new SqlConnection(cs);

string query = "select * from city where c_id = @country_id";

SqlDataAdapter sda = new SqlDataAdapter(query, con);

sda.SelectCommand.Parameters.AddWithValue("@country_id",country_id);

DataTable data = new DataTable();

sda.Fill(data);

CityDropDownList.DataSource = data;

CityDropDownList.DataTextField = "city_name";

CityDropDownList.DataValueField = "city_id";

CityDropDownList.DataBind();

ListItem selectItem = new ListItem("Select City", "Select City");

selectItem.Selected = true;

CityDropDownList.Items.Insert(0, selectItem);

}

protected void CountryDropDownList_SelectedIndexChanged(object sender, EventArgs e)

{

try

{

int country_id = Convert.ToInt32(CountryDropDownList.SelectedValue);

BindCityDDL(country_id);

}

catch(Exception ex)

{

Response.Write("<script>alert('Country is Required')</script>");

}

protected void SubmitButton_Click(object sender, EventArgs e)

{

Response.Write("Selected Country is : " + CountryDropDownList.SelectedItem.ToString() + "<br>");

Response.Write("Selected Country Id is : " + CountryDropDownList.SelectedValue.ToString() + "<br>");

Response.Write("Selected City is : " + CityDropDownList.SelectedItem.ToString() + "<br>");

Response.Write("Selected City Id is : " + CityDropDownList.SelectedValue.ToString() + "<br>");

}

Above File is BindingDDL\WebForm1.aspx.cs

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="BindingDDL.WebForm1" %>

<!DOCTYPE html>

.auto-style1 {

width: 100%;

}

.auto-style2 {

width: 70px;

}

</style>

</head>

<body>

<div>

<tr>

<td class="auto-style2">Country</td>

<td>

<asp:DropDownList ID="CountryDropDownList" runat="server" AutoPostBack="True" Height="39px" OnSelectedIndexChanged="CountryDropDownList_SelectedIndexChanged" Width="209px">

</asp:DropDownList>

<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="CountryDropDownList" Display="Dynamic" ErrorMessage="Country is Required" ForeColor="Red" InitialValue="Select Country" SetFocusOnError="True"></asp:RequiredFieldValidator>

</td>

</tr>

<tr>

<td>

<asp:DropDownList ID="CityDropDownList" runat="server" Height="39px" Width="209px">

</asp:DropDownList>

<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="CityDropDownList" Display="Dynamic" ErrorMessage="City is Required" ForeColor="Red" InitialValue="Select City" SetFocusOnError="True"></asp:RequiredFieldValidator>

</td>

</tr>

<tr>

<td>

<asp:Button ID="SubmitButton" runat="server" OnClick="SubmitButton_Click" Text="Submit" />

</td>

</tr>

</table>

</div>

</form>

</body>

</html>