Cascading Drop downlist in ASP.NET

1. Country
2. States

Objective

1. Understanding Cascading 
2. Fetching states from database on the selection of the country.

Using the code

// Table and Stored Procedure

-- Table for Country
CREATE TABLE [dbo].[Country](
	[CounrtyID] [int] NULL,
	[CounrtyName] [varchar](50) NULL
) ON [PRIMARY]

GO


---- Table for States
CREATE TABLE [dbo].[States](
	[StateID] [int] IDENTITY(1,1) NOT NULL,
	[CountryID] [int] NULL,
	[StateName] [varchar](50) NULL
) ON [PRIMARY]

GO

--Stored Proc for Getting Countries
ALTER proc [dbo].[GetCountries]
as
begin
select * from Country
end


----Stored Proc for Getting Countries
ALTER proc [dbo].[getStates]
(
@CountryID int
)
as
begin
select * from States where CountryID = @CountryID
end

// HTML Mark up and Code behind

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;

public partial class CascadingDropDownt : System.Web.UI.Page
{
    string errdesc = "0";
    SqlConnection sqlconn = new SqlConnection("Data Source=.;Initial Catalog=DotNetFunda;Persist Security Info=True;User ID=sa;Password=sqluser");
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            // Function called on page load to bind countries

            BindCountries();
        }
    }


    // Function to Bind Countries
    private void BindCountries()
    {
        try
        {
            
            sqlconn.Open();
            DataSet dscountry = new DataSet();

            // Calling the Stored Procedure of Get Countries
            SqlCommand cmd = new SqlCommand("GetCountries", sqlconn);
            cmd.CommandType = CommandType.StoredProcedure;
            SqlDataAdapter dacountry = new SqlDataAdapter(cmd);
            dacountry.Fill(dscountry, "Country");
            xddlCountry.DataSource = dscountry;
           
            if (dscountry.Tables[0].Rows.Count > 0)
            {
                
                xddlCountry.DataTextField = "CounrtyName";
                xddlCountry.DataValueField = "CounrtyID";
                xddlCountry.DataBind();
                xddlCountry.Items.Insert(0, new ListItem("----Select Country----"));
            }
        }
        catch (Exception ex)
        {
            errdesc = ex.Message;
        }
        finally
        {
            sqlconn.Close();
        }

    }

    // Binding States on the base of the selection of the country on select Index Change
    protected void xddlCountry_SelectedIndexChanged(object sender, EventArgs e)
    {
        try
        {
            sqlconn.Open();
            DataSet dsstates = new DataSet();

            // Calling the Stored Procedure of getstates 
            SqlCommand cmd = new SqlCommand("getStates", sqlconn);
            cmd.CommandType = CommandType.StoredProcedure;

            // Passing the parameter to the stored procedure to get the States on the selection of the country
            cmd.Parameters.AddWithValue("@CountryID", SqlDbType.Int).Value = xddlCountry.SelectedValue; 
            SqlDataAdapter dastates = new SqlDataAdapter(cmd);
            dastates.Fill(dsstates, "States");
            xddlState.DataSource = dsstates;

            if (dsstates.Tables[0].Rows.Count > 0)
            {
                xddlState.Enabled = true;
                xddlState.DataTextField = "StateName";
                xddlState.DataValueField = "StateID";
                xddlState.DataBind();
            }
        }
        catch (Exception ex)
        {
            errdesc = ex.Message;
        }
        finally
        {
            sqlconn.Close();
        }

    }
}

Conclusion