Displaying only related values in box 2 based on option selecting in box1 in ASP.Net

Hi,

Consider you have the dropdowns

1. Dropdown1
2. Dropdown2

Load the first drop down values in the page load.

Dropdown1.DataSource = DataSet1.Tables[0];
Dropdown1.DataTextField = "Name";
Dropdown1.DataValueField = "ID"; 
Dropdown1.DataBind();

Enable the autopostback property for the first dropdown; and write the index changed event.

protected void  Dropdown1_OnInexchanged(object sender, EventArgs e)
{
        int _Id =  Convert.ToInt32(Dropdown1.SelectedItem.Value.ToString());
        //Load the data based on the ID and get some datatable/DataSet/Collection
         Dropdown2.DataSource = DataSet2.Tables[0];
        Dropdown2.DataTextField = "Name1";
        Dropdown2.DataValueField = "ID1"; 
        Dropdown2.DataBind(); 
}

You can use the AJAX update panel to reload the page again when select in the first drop down.