ASP.NET PreInit() and IsPostBack property

What does PreInit() do by checking IsPostBack property?

Genererally while explaining PreInit() lot webpages s开发者_运维技巧ay it checks IsPostBack property. But they don't tell what will PreInit do if IsPostBack is true or IsPostBack is false?

It's explained here ( http://msdn.microsoft.com/en-us/library/ms178472.aspx ) that you can use the value of IsPostBack to determine if it's a postback or not. If it is a postback the values of the controls on the page will not be set yet.

If page is posted, role of preinit to load the data existed on page before post.