When a dropdownlist has been added by some records and it
has been binded why it is not executing i'm facing this
error pls help me ?

if (is!pageposback)

{
arraylist books = new arraylist;
books.add ("gone with the wind");
books.add ("rahulsriramprakash");
books.add ("vishal");
dropdowndisplay.datasource=books;
dropdowndisplay.databind();
}

The error is :

1) The dropdowndisplay does not exist.