Trouble implementing ICurrentUserInformationProvider

In my code below, the commented out loggedUserRow line uses an obsolete method.  I tried to implement the ICurrentUserInformationProvider to get the User ID.  When the code runs, the _currentUserInformationProvider variable is null.  I’m not sure what I need to do to instantiate the variable.  This is probably a c# thing.  I tried a bunch of things not shown here, but I couldn’t figure out how to implement that interface.  

        public ICurrentUserInformationProvider _currentUserInformationProvider { get; set; }

        #region Events
        protected virtual void _(Events.FieldUpdated<SOLine, SOLine.inventoryID> e)
        {
            if (e.Row == null)
            {
                return;
            }

            SOLine lineRow = (SOLine)e.Row;

            //Users loggedUserRow = Users.PK.Find(this.Base, PXAccess.GetUserID());

            System.Guid? u = _currentUserInformationProvider.GetUserId();

            Users loggedUserRow = Users.PK.Find(this.Base, u.Value);

            if (loggedUserRow != null)
            {
                UsersSSGExt loggedUserExtRow = this.Base.Caches[typeof(Users)].GetExtension<UsersSSGExt>(loggedUserRow);
                if (loggedUserExtRow != null
                        && loggedUserExtRow.UsrSSGDefaultWHS != null)
                {
                    lineRow.SiteID = loggedUserExtRow.UsrSSGDefaultWHS;
                }
            }
        }
        #endregion