This member overrides Control.OnInit(EventArgs), and more complete documentation might be available in that topic.
Assembly: System.Web (in System.Web.dll)
Web server controls should perform any initialization steps that are required to create and set up an instance. You cannot use view state information within this event; it is not populated yet. You should not access another Web server control during the method, regardless of whether it is a child or parent to the ChangePassword control. Other Web server controls are not certain to be created and ready for access.