Viewstate object is used to persist data of variables across postbacks. In ASP.NET, a variable's value is assigned to a viewstate object and then this is passed as a hidden variable and then may be retrieved by a page after a postback. See the example below...
//Save the value in ViewState object before the PostBack
ViewState("SomeVar") = txtFirstName.text;
//Retrieve the value from ViewState object after the PostBack
String strFirstName = ViewState("SomeVar").ToString();
Note that Viewstate object's value is accessible only at page level. This means that if a viewstate is created at page1.aspx, then it may be used only within page1.aspx after the postback, and cannot be used by any other page.
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