I wanted the ASP .Net AJAX Toolkit's Modal Popup Extender to appear at some condition, not at the click of a button, that checks that condition.
I accomplished this extender to some dummy button and made that button hide. Whereas called PopupObj.Show() method on the desired condition. But there is still a problem that the popup appear without PostBack only on the click event of the button with whcih it was made. You cannot set TargetControlID of the popupExtender object to any other button on runtime and achieve that functionality.
Instead you can use Update panel for this pupose.