why and when to use view state session and application state

First I will provide you the following definitions from MSDN for them:

Session: Session variables are stored in a SessionStateItemCollection object that is exposed through the HttpContext.Session property. In an ASP.NET page, the current session variables are exposed through the Session property of the Page object.

More about Sessions: http://msdn.microsoft.com/en-us/library/ms178581(v=vs.100).aspx[^]


ViewState: Microsoft® ASP.NET view state, in a nutshell, is the technique used by an ASP.NET Web page to persist changes to the state of a Web Form across postbacks.

More about Viewstate: http://msdn.microsoft.com/en-us/library/ms972976.aspx[^]


Application: You can use the Application object to share information among all users of a given application. An ASP-based application is defined as all the .asp files in a virtual directory and its subdirectories. Because the Application object can be shared by more than one user, there are Lock and Unlock methods to ensure that multiple users do not try to alter a property simultaneously.

More about Application: http://msdn.microsoft.com/en-us/library/ms525360(v=vs.90).aspx[^]


How to Choose From Viewstate, Session, Application, Cache, and Cookies: http://www.articlesbase.com/programming-articles/how-to-choose-from-viewstate-session-application-cache-and-cookies-443393.html
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Cache, Session, and ViewState: Cache, Session, and ViewState[^]


Hope this information helps you...