This technique works with WebForms, but becomes much more useful when you site WebUserControls on a WebForm and need to set/get values between the parent Form and a child UserControl.
Put something like this in your WebUserCotrol1.
public int Total {
get { return ViewState["intTotal"] != null ? Int32.Parse(ViewState["intTotal"].ToString()) : 0; }
set { ViewState["intTotal"] = value; }
}
Site the UserControl on WebForm1.
Then you can access the Property in the UserControl from WebForm1’s code behind like this.
int newTotal = this.WebUserControl1.Total;
Simple.. ViewState will hold the value between postbacks..
Joel Holder's Code Compendium 