void EditSalesOrder(string SONumber)
        {
            bool SOWorkspaceExist = false;
            //SalesOrderViewModel Constructor takes SOnumber as param
            //SONumber for edit sales order
            SalesOrderViewModel workspace = new SalesOrderViewModel(SONumber);

            if (this.Workspaces.Count > 0)
            {
                SOWorkspaceExist = workSpaceExist(Workspaces, "SalesOrderViewModel");
            }

            //if this work space is not exist
            if (!SOWorkspaceExist)
            {
                this.Workspaces.Add(workspace);
                this.SetActiveWorkspace(workspace);
            }
        }
        void CreateNewSalesOrder()
        {
            bool SOWorkspaceExist = false;
            //SalesOrderViewModel Constructor takes SOnumber as param
            //empty string for new sales order

            SalesOrderViewModel workspace = new SalesOrderViewModel("");

            if (this.Workspaces.Count > 0)
            {
                SOWorkspaceExist = workSpaceExist(Workspaces, "SalesOrderViewModel");
            }

            //if this work space is not exist
            if (!SOWorkspaceExist)
            {
                this.Workspaces.Add(workspace);
                this.SetActiveWorkspace(workspace);
            }
        }