导出Excel如何把数字转成文本呀？
SaveFileDialog saveFileDialog = new SaveFileDialog();
  saveFileDialog.Filter = "Execl files (*.xls)|*.xls";
  saveFileDialog.FilterIndex = 0;
  saveFileDialog.RestoreDirectory = true;
  saveFileDialog.Title = "Export Excel File";
  saveFileDialog.ShowDialog();
  if (saveFileDialog.FileName == "")
  return;
  Stream myStream;
  myStream = saveFileDialog.OpenFile();
  StreamWriter sw = new StreamWriter(myStream, System.Text.Encoding.GetEncoding(-0));
  string str = "";
  try
  {
  //寫dataGridView1表標題
  for (int i = 0; i < dataGridView1.ColumnCount; i++)
  {
  if (i > 0)
  {
  str += "\t";
  }
  str += dataGridView1.Columns[i].HeaderText.Trim();
  }
  sw.WriteLine(str);

  //寫dataGridView1表內容
  for (int j = 0; j < dataGridView1.Rows.Count; j++)
  {
  string tempStr = "";
  for (int k = 0; k < dataGridView1.Columns.Count; k++)
  {
  if (k > 0)
  {
  tempStr += "\t";
  }  
  tempStr += dataGridView1.Rows[j].Cells[k].Value;

//要增加對含數字的文字類，如身份証號
//.........欠對身份証號處理，以免在EXCEL打開時被自動轉數字
  }
  sw.WriteLine(tempStr);
  }
  sw.Close();
  myStream.Close();
  }

  catch (Exception ex)
  {
  MessageBox.Show(ex.ToString());
  }
  finally
  {
  sw.Close();
  myStream.Close();
  }

------解决方案--------------------
tempStr += dataGridView1.Rows[j].Cells[k].Value;
改成
tempStr += "=\"" + dataGridView1.Rows[j].Cells[k].Value + "\"";