OnPreInit Event in Page Life Cycle

1. This event occurs only for the Page class and UserControls/MasterPages do not have this method to override.
2. Note that PreInit() is the only event where we can set themes programmatically.

Special Case with MasterPages

1. It is important to note that Master Page is treated like a control in the Content Pages.
2. So if a Page has a Master Page associated with it, then the controls on the page will not be initialized and would be null in this stage. Only after the Init() event starts,
   you can access these controls directly from the page class.
3. The reason being that all controls placed in the Content Page are within a ContentPlaceholder which is a child control of a MasterPage. Now Master Page is merged and treated like a control in the Content Pages. As I mentioned earlier, all events except the Init() and Unload() are fired from outermost to the innermost control. So PreInit() in the Page is the first event to fire but User Controls or MasterPage (which is itself a Usercontrol) do not have any PreInit event . Therefore in the Page_PreInit() method, neither the MasterPage nor any user control has been initialized and only the controls inside the Page class are set to their default values. Only after the Page_PreInit() event the Init() events of other controls fire up.

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