ViewState
It is allows the state of objects to be stored in a hidden field on the page. It is transported to the client and back to the server, and is not stored on the server or any other external source. It is used to retain the state of server-side objects between post backs.
Enable ViewState Property
It allows the page to save the users input on a form across post backs. It saves the server-side values for a given control into view state, which is stored as a hidden value on the page before sending the page to the client’s browser.