<Newbie>

How can I get arguments, and build a query URL, before a button is pressed?

I have a text box to enter a serial number.  When the search button is
pressed, I wish append the serial number text to the URL and navigate to
the search results page.  I tried the button click event, but this does
not work until the second click.  What is a better way to accomplish the
desired behavior?

private const string urlQuery = @"~/queryPage.aspx?serialNumber=";

protected void btnQuery_Click(object sender, EventArgs e)
{
   btnQuery.PostBackUrl = urlQuery + txtSerialNumber.Text;
}

Thanks in advance for any tips or suggestions,

-Ed