The OnPreInit method is called at the beginning of the page initialization stage.
After the OnPreInit method is called, personalization information is loaded and the page theme, if any, is initialized. This is also the preferred stage to dynamically define a PageTheme or MasterPage for the Page.
Raising an event invokes the event handler through a delegate. For more information, see Handling and Raising Events.
The OnPreInit method also allows derived classes to handle the event without attaching a delegate. This is the preferred technique for handling the event in a derived class.
Notes to Inheritors: When overriding OnPreInit in a derived class, be sure to call the base class's OnPreInit method so that registered delegates receive the event.