you can do as follow:
page_load()
{
if(!ispostback)
{
binddropdown1();
}
}
dropdown1_selectedchange()
{
binddropdown2();
}
dropdown2_selectedchange()
{
binddropdown3();
}
dropdown3_selectedchange()
{
binddropdown4();
}
binddropdown1()
{
dropdown2, dropdown3, dropdown4.clear();
dropdown1.datasource = dt;
dropdown1.textfield = ""
dropdown1.datafield = "";
dropdown1.selectedindex = 0;
}
binddropdown2()
{
dropdown3, dropdown4.clear();
dropdown2.datasource = dt; where fieldid = dropdown1.selectedvalue;
dropdown2.textfield = ""
dropdown2.datafield = "";
}
binddropdown3()
{
dropdown4.clear();
dropdown3.datasource = dt; where fieldid = dropdown2.selectedvalue;
dropdown3.textfield = ""
dropdown3.datafield = "";
}
binddropdown4()
{
dropdown4.datasource = dt; where fieldid = dropdown3.selectedvalue;
dropdown4.textfield = ""
dropdown4.datafield = "";
}