DataGridView导出Excel 隐藏列不显示

 //导出Excel
        private void btnExc_Click(object sender, EventArgs e)
        {
            string filename = "成绩查询数据--" + DateTime.Now.ToString("yyMMddhhmmss");
            string saveFileName = "";
            SaveFileDialog saveDialog = new SaveFileDialog();
            saveDialog.DefaultExt = "xls";
            saveDialog.Filter = "Excel文件|*.xls";
            saveDialog.FileName = filename;
            saveDialog.ShowDialog();
            saveFileName = saveDialog.FileName;
            if (saveFileName.IndexOf(":") < 0) return; //被点了取消
            Microsoft.Office.Interop.Excel.Application xlApp = new Microsoft.Office.Interop.Excel.Application();
            if (xlApp == null)
            {
                MessageBox.Show("无法创建Excel对象，可能你的机器上没有安装Excel！");
                return;
            }

            Microsoft.Office.Interop.Excel.Workbooks workbooks = xlApp.Workbooks;
            Microsoft.Office.Interop.Excel.Workbook workbook = workbooks.Add(Microsoft.Office.Interop.Excel.XlWBATemplate.xlWBATWorksheet);
            Microsoft.Office.Interop.Excel.Worksheet worksheet = (Microsoft.Office.Interop.Excel.Worksheet)workbook.Worksheets[1];//取得sheet1
            int colIndex = 0;
            //写入标题
            for (int i = 0; i < dgvScore.ColumnCount; i++)
            {
                if (dgvScore.Columns[i].Visible)
                {
                    colIndex++;
                    worksheet.Cells[1, colIndex] = dgvScore.Columns[i].HeaderText;
                }
            }
            //写入数据
            for (int r = 0; r < dgvScore.Rows.Count; r++)
            {
                colIndex = 0;
                for (int i = 0; i < dgvScore.ColumnCount; i++)
                {
                    if (dgvScore.Columns[i].Visible)
                    {
                        colIndex++;
                        worksheet.Cells[r + 2, colIndex] = dgvScore.Rows[r].Cells[i].Value;
                    }
                }
                System.Windows.Forms.Application.DoEvents();
            }
            worksheet.Columns.EntireColumn.AutoFit();//列宽自适应
            if (saveFileName != "")
            {
                try
                {
                    workbook.Saved = true;
                    workbook.SaveCopyAs(saveFileName);
                }
                catch (Exception ex)
                {
                    MessageBox.Show("导出文件时出错,文件可能正被打开！\n" + ex.Message);
                    return;
                }
            }
            xlApp.Quit();
            GC.Collect();//强行销毁
            MessageBox.Show(filename + "文件导出成功", "提示", MessageBoxButtons.OK);

        }