关于在不知道具体实例化哪个窗体时调用该窗体公共变量的方法

        private Form NewForm(string formName)
        {
            switch (formName)
            {
                case "rechargePayManage":
                    return new rechargePayManage();
                case "FormProjectRefund":
                    return new FormProjectRefund();
                case "FormExport":
                    return new FormExport();
                case "FormAFTicketOping":
                    return new FormAFTicketOping();
                case "Group_tax_manage":
                    return new Group_tax_manage();
                default:
                    return new rechargePayManage();
            }
        }  

Form frm = NewForm(formName);
frm.GetType().GetField(“testKey”).SetValue(frm,"testValue");