In an earlier post I mentioned my struggle with the ProgressUpdate control. In many situations it would be helpful to place the progress indicator right in the middle of the page so users always have an idea something is happening. The problem with this is, well, Internet Explorer < 7 .0 which treats lists (dropdowns, list boxes) as windowed controls, so they always show on top of other HTML elements.

When Shane Shepherd posted a couple of links to workarounds, it all came full circle. I ended up writing an extender control which attaches to any ASP.NET control and centers it dead-center during an AJAX callback. The included sample uses an animated glyph lifted from here but you’re free to use whatever you want.

I had a chance to test this in IE 6, Firefox and Opera. I don’t have Safari at the moment. Download the source code here and simply open CenteredProgressIndicatorTest in Visual Studio as a web site.

I remember seeing a sample which used Sys.Application.add_load to attach a function you’d normally want to run upon window.onload. It went like this:

function initFoo () {
  // Initialization code here...
}

Sys.Application.add_load (initFoo);

Having browsed the MS AJAX Library source code, I figured the Sys.Application provided a convenient event hook indeed since the class tapped window.load and window.unload for you:

Sys.UI.DomEvent.addHandler (
   window, "unload", this._unloadHandlerDelegate);

Sys.UI.DomEvent.addHandler (
   window, "load", this._loadHandlerDelegate);

To my surprize, initFoo was getting called on every AJAX callback. I figured there was no way get window to fire its onload event several times, so the Sys.Application class must’ve been involved a lot more than I thought.

The remedy is to either hook into window.onload directly:

Sys.UI.DomEvent.addHandler(window, "load", initFoo);

or avoid multiple initializations:

function initFoo () {
  var prm = Sys.WebForms.PageRequestManager.getInstance();

 if (prm.get_isInAsyncPostBack())
     return;

 // Initialization code here...
}

To me, the former looks cleaner and less kludgy than the latter.