What exactly does a server control e.g. a TextBox do, around the time it fires its Init event?

Question

My understanding is a server control's constructor is called by the page's constructor. This happens before Page_PreInit event. A server control's Init event fires after Page_PreInit. It seems a server control does not do much during the Init stage? Then why bother giving much emphasis to Init stage?

Answer 1

I'm not entirely sure this is what you're looking for but a TextBox control inherits from System.Web.UI.WebControls.WebControl which in turn inherits from System.Web.UI.Control which is the object that defines the Init event regardless of whether the TextBox control requires it or not.
Whether this event is used or not depends on the requirement of the control inheriting this object. If you were wanting to create a custom web control and you needed to do something at the initialisation stage then you can access this stage via the OnInit method.
Hope this helps.

Answer 2

The server control constructor is called in Page.ProcessRequest, which is after the Page's constructor has fired. You are correct that the initial control tree is completely created by the time Page_PreInit is called. Initializing a control in its constructor is too early for many controls, because Control.Page is null (it is set after the server control is created and the control is added to the control tree).

TextBox doesn't make much use of the earlier parts of the page lifecycle. Other controls, like GridView or the Repeater, do though. The key difference between Init and Load, is that Init occurs before viewstate is loaded, and Load occurs after. You're not going to understand the purpose of Init until you truly understand viewstate.