Viewstate entity

 //view state declaration
    List<CheckVoucher> viewStateCheckVoucher
    {
        get { return (List<CheckVoucher>)ViewState["CheckVoucher"]; }
        set { ViewState["CheckVoucher"] = value; }
    }

in page load initialize
 if (viewStateCheckVoucher == null) viewStateCheckVoucher = new List<CheckVoucher>();//view state initialisation