datagridview 保存为excel输出

private void btn_Out_Click(object sender, EventArgs e)
        {
            
            string fileName = "";
            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，您的电脑可能未安装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 
            btn_Out.Enabled = false;
            btn_Out.Text = "请稍后";
            //写入标题             
            for (int i = 0; i < datagv_List.ColumnCount; i++)
            {
                worksheet.Cells[1, i + 1] = datagv_List.Columns[i].HeaderText;
            }
            //写入数值
            for (int r = 0; r < datagv_List.Rows.Count; r++)
            {
                for (int i = 0; i < datagv_List.ColumnCount; i++)
                {
                    worksheet.Cells[r + 2, i + 1] = datagv_List.Rows[r].Cells[i].Value;
                }
                System.Windows.Forms.Application.DoEvents();
            }
            worksheet.Columns.EntireColumn.AutoFit();//列宽自适应
            MessageBox.Show( "保存成功", "提示", MessageBoxButtons.OK);
            if (saveFileName != "")
            {
                try
                {
                    workbook.Saved = true;
                    workbook.SaveCopyAs(saveFileName);  //fileSaved = true;                 
                }
                catch (Exception ex)
                {//fileSaved = false;                      
                    MessageBox.Show("导出文件时出错,文件可能正被打开！\n" + ex.Message);
                }
            }
            xlApp.Quit();
            GC.Collect();//强行销毁        
            btn_Out.Enabled = true;
            btn_Out.Text = "保存";
        }