How can I react to two events on one postback

I am trying to develop a Web User Control that allows me to copy/paste data from a spreadsheet to a user-defined table controlled by SQL and managed by my ASP.NET web page. Data is pasted into the first row (row 0) of a gridview, and then distributed into rows and columns by server-side code.
This Help page describes what I've done: -
        http://www.famnet.net.nz/help/Uploading_Data_from_a_Spreadsheet.htm
The row 0 cells into which one posts data are defined (dynamically) with: -
                        Dim tb As TextBox = DirectCast(item.Controls(0), TextBox)
                        tb.TextMode = TextBoxMode.MultiLine
            ...