Cascading DropDownlist

We have three tables  1)tblcontinents 2)tblCountry  3)tblState
Stored Procedure for the above named tables for doing operation in Cascading DropDownlist

create proc [dbo].[SP_GetContinent]
as
begin
select Continentid,Continentname from dbo.tblcontinents
end

create proc [dbo].[SP_GetCountriesByContinentID]
@Continent_id int
as
begin
select Countryid,Countryname from dbo.tblCountry where Continent_id =@Continent_id
end

create proc [dbo].[SP_GetStatesByCountry]
@Country_id int
as
begin
select Stateid,Statename from dbo.tblState where Country_id =@Country_id
end

We have to design as like below 

<asp:DropDownList ID="DDL_Continent" runat="server" Width="150px"  CausesValidation="true"

                        DataTextField="Continentname" DataValueField="Continentid"  AutoPostBack="true" 

                        onselectedindexchanged="DDL_Continent_SelectedIndexChanged" TabIndex="10">

                    </asp:DropDownList>

<asp:DropDownList ID="DDL_Country" runat="server" Width="150px" 

                        DataTextField="Countryname" DataValueField="Countryid" 

                        onselectedindexchanged="DDL_Country_SelectedIndexChanged" TabIndex="11" AutoPostBack="true">

                    </asp:DropDownList>

<asp:DropDownList ID="DDL_City" runat="server" Width="150px" 

                        DataTextField="Statename" DataValueField="Stateid"  TabIndex="12" AutoPostBack="true">

                        

                    </asp:DropDownList>

 This  is  reusable stored procedure function

private DataSet GetData(string spname, SqlParameter Parameter)

    {

        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["DBConn"].ConnectionString);

        SqlDataAdapter da = new SqlDataAdapter(spname, con);

        da.SelectCommand.CommandType = CommandType.StoredProcedure;

        if (Parameter != null)

        {

            da.SelectCommand.Parameters.Add(Parameter);

        }

        ds = new DataSet();

        da.Fill(ds);

        return ds;

    }

protected void DDL_Continent_SelectedIndexChanged(object sender, EventArgs e)

    {

        if (DDL_Continent.SelectedIndex == 0)

        {

            DDL_Country.SelectedIndex = 0;

            DDL_Country.Enabled = false;

            DDL_City.SelectedIndex = 0;

            DDL_City.Enabled = false;

        }

        else

        {

            DDL_Country.Enabled = true;

            SqlParameter par = new SqlParameter("@Continent_id", DDL_Continent.SelectedValue);

            ds = new DataSet();

            ds = GetData("SP_GetCountriesByContinentID", par);

            DDL_Country.DataSource = ds;

            DDL_Country.DataBind();

            ListItem li = new ListItem("Select Country", "-1");

            DDL_Country.Items.Insert(0, li);

            DDL_City.SelectedIndex = 0;

            DDL_City.Enabled = false;

        }

    }

    protected void DDL_Country_SelectedIndexChanged(object sender, EventArgs e)

    {

        if (DDL_Country.SelectedIndex == 0)

        {

            DDL_City.SelectedIndex = 0;

            DDL_City.Enabled = false;

        }

        else

        {

            DDL_City.Enabled = true;

            SqlParameter par = new SqlParameter("@Country_id", DDL_Country.SelectedValue);

            ds = new DataSet();

            ds = GetData("SP_GetStatesByCountry", par);

            DDL_City.DataSource = ds;

            DDL_City.DataBind();

            ListItem li = new ListItem("Select City", "-1");

            DDL_City.Items.Insert(0, li);

            DDL_City.SelectedIndex = 0;

            DDL_City.Enabled = true;

        }

    }

We have to call this below method in Page_Load event

    private void Initial_PageLoad()

    {

        DDL_Continent.DataSource = GetData("SP_GetContinent", null);

        DDL_Continent.DataBind();

        ListItem licont = new ListItem("Select Continent", "-1");

        DDL_Continent.Items.Insert(0, licont);

        ListItem liCountry = new ListItem("Select Country", "-1");

        DDL_Country.Items.Insert(0, liCountry);

        ListItem liCity = new ListItem("Select City", "-1");

        DDL_City.Items.Insert(0, liCity);

    }