View state is one of the feature of Client side State Management technique under the ASP.Net State Management. It is a way to preserve the value of the page and controls between round trips.
Suppose you have a webform with
two text fields namely user name and password along with
2 button namely submit and restore.
In the above case if we dont use view state than, after the submit button is clicked the value of user name and password is submitted to the server. We cannot restore the value again because after the postback instance, the control is destroyed and upon clicking of the restore Button the server takes a new request and the server cannot restore the value of the TextBox.
BUT if we use view state than, after clicking on the submit Button the value of user name and password is submitted in view state and the view state stores the value of user name and password during post-back and upon clicking on the restore button we can get the value again.