導出EXCEL代碼(C#)

try
...{   string filename;
SaveFileDialog sfd = new SaveFileDialog();
sfd.Title = "請選擇將導出的Excel文件存放路徑";
sfd.Filter="Excel文檔(*.xls)|*.xls";
//sfd.OpenFile(); 
sfd.ShowDialog();
if (sfd.FileName != "")
...{
if(sfd.FileName.LastIndexOf(".xls")<=0)
...{
sfd.FileName=sfd.FileName+".xls";
}
filename=sfd.FileName;
if(System.IO.File.Exists(filename))
...{
System.IO.File.Delete(filename);  
}
Excel.ApplicationClass xlApp = new Excel.ApplicationClass();
if (xlApp == null)

...{
MessageBox.Show("無法創建Excel對象，可能您的機器未安裝Excel");
return;
}
Excel.Workbooks workbooks = xlApp.Workbooks;
Excel.Workbook workbook = workbooks.Add(Excel.XlWBATemplate.xlWBATWorksheet);
Excel.Worksheet worksheet = (Excel.Worksheet)workbook.Worksheets[1];
DataTable dt1 = (DataTable)dataGrid2.DataSource;
float percent=0;
long rowRead=0;
if(dt1==null) 
...{
MessageBox.Show("1");
return;
}
long totalCount=dt1.Rows.Count; 
this.progressBar1.Visible=true;
for (int i = 0; i < dt1.Rows.Count; i++)
...{
this.progressBar1.Value=i;
for (int j = 0; j < dt1.Columns.Count; j++)
...{
if (i == 0)
...{
worksheet.Cells[1, j + 1] = dt1.Columns[j].ColumnName;
}
worksheet.Cells[i + 2, j + 1] = dt1.Rows[i][j].ToString();
}
rowRead++;
percent=((float)(100*rowRead))/totalCount;    
this.progressBar1.Text= "正在導出數據["+ percent.ToString("0.00")  +"%]...";
}
                    this.progressBar1.Visible=false;
workbook.Saved = true;
workbook.SaveCopyAs(filename);
System.Runtime.InteropServices.Marshal.ReleaseComObject(worksheet);
worksheet = null;
System.Runtime.InteropServices.Marshal.ReleaseComObject(workbook);
workbook = null;
workbooks.Close();
System.Runtime.InteropServices.Marshal.ReleaseComObject(workbooks);
workbooks = null;
xlApp.Quit();
System.Runtime.InteropServices.Marshal.ReleaseComObject(xlApp);
xlApp = null;
MessageBox.Show("導出Excel完成!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information);
//button2_Click(null,null);

}
}
catch(Exception ex)
...{
MessageBox.Show("導出Excel失敗!"+ex.Message,"錯誤",MessageBoxButtons.OK,MessageBoxIcon.Information);
}