模式窗体——返回

                FormZFGLForPay frm = new FormZFGLForPay();
                if (DialogResult.OK == frm.ShowDialog())       //以此来判断确定还是取消
                {
                }

弹出窗体，点击确定后，将  DialogResult = System.Windows.Forms.DialogResult.OK;

         点击取消，将DialogResult = System.Windows.Forms.DialogResult.Cancel;