VIEWSTATE allows the state of objects (serializable) to be stored in a hidden field on the page. ViewState is transported to the client and back to the server, and is not stored on the server or any other external source. ViewState is used the retain the state of server-side objects between postabacks. Data stored in VIEWSTATE is base-64 encoded.
ViewState available? The view state is available after the Init() and before the Render() methods are called during Page load.
After the Init() and before the Page_Load(), or OnLoad() for a control.
EnableViewState" property do
It allows the page to save the users input on a form across postbacks. It saves the server-side values for a given control into ViewState, which is stored as a hidden value on the page before sending the page to the clients browser. When the page is posted back to the server the server control is recreated with the state stored in viewstate.
Session state vs. View state:
In some cases, using view state is not feasible. The alternative for view state is session state. Session state is employed under the following situations:
o Large amounts of data - View state tends to increase the size of both the HTML page sent to the browser and the size of form posted back. Hence session state is used.
o Secure data - Though the view state data is encoded and may be encrypted, it is better and secure if no sensitive data is sent to the client. Thus, session state is a more secure option.
o Problems in serializing of objects into view state - View state is efficient for a small set of data. Other types like DataSet are slower and can generate a very large view state.