Scroll to top of page after async post back - asp.net

Question

So I need to scroll to the top of the page after an async post back in an asp.net update panel.
The code I used was this:
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestEventHandler);
function EndRequestEventHandler(sender, args)
{
scrollTo(0,0);
}
However, I only want this to be run when I click on a certain button which causes the async postback.
How do I wire this event up in my code behind button event?
Any help would be appreacited, thanks!

Answer 1

My quest for a solution is finally over. This question was part of the help, and the rest I found here.
Had to override ASP.NET Ajax's behaviour of memorizing the scroll position:
<script type="text/javascript">
var manager = Sys.WebForms.PageRequestManager.getInstance();
manager.add_beginRequest(beginRequest);
function beginRequest()
{
manager._scrollPosition = null;
}
</script>
And then use the bit of code in the answer here, on the codebehind of the page I wanted to scroll to the top:
ScriptManager.RegisterStartupScript(this, typeof(MyControl), "someText", "window.scrollTo(0, 0)", true);

Answer 2

I used Farinha's answer (thanks!) and changed it slightly so I could just call the method any place I wanted to scroll to the top, but maintain the scroll position otherwise.
public static void ScrollToTop(int intPosY = 0)
{
string strScript = #"var manager = Sys.WebForms.PageRequestManager.getInstance();
manager.add_beginRequest(beginRequest);
function beginRequest()
{
manager._scrollPosition = null;
}
window.scroll(0," + intPosY.ToString() + ");";
Page pagCurrent = GetCurrentPage();
ScriptManager.RegisterStartupScript(pagCurrent, pagCurrent.GetType(), string.Empty, strScript, true);
return;
}
public static Page GetCurrentPage()
{
return (HttpContext.Current.Handler as Page);
}

Answer 3

Try this:
protected void myButon_Click(object sender, EventArgs e)
{
ScriptManager.RegisterStartupScript(this, typeof(MyControl), "someText", "alert('!');", true);
}

Answer 4

Improving on the answers of #Farinha and #Bradford Scott, the code can be simplified to this:
var script =
"Sys.WebForms.PageRequestManager.getInstance()._scrollPosition = null; " +
"window.scrollTo(0, 0);"
ScriptManager.RegisterStartupScript(this, GetType(), "key", script, true);
I'm actually not even sure why their scripts work since they add the reset of the Sys.WebForms.PageRequestManager's _scrollPosition as an add_beginRequest handler, and here we are actually returning from the request.
Anyway, resetting the _scrollPosition right before making your own scrollTo() call definitely works.