数据导出只导出当前页的，不能导出全部数据。
代码如下：
 if (dataGridView1.Rows.Count == 0)
  {
  MessageBox.Show("表格中无数据导出");
  return;
  }

  SaveFileDialog dlg = new SaveFileDialog();

  if (this.ckTXT.Checked)
  {
  dlg.Filter = "Text files (*.txt)|*.txt";

  if (dlg.ShowDialog() == DialogResult.OK)
  {
  Stream myStream = dlg.OpenFile();
  StreamWriter sw = new StreamWriter(myStream, System.Text.Encoding.GetEncoding("gb2312"));
  string strTitle = "";
  //生成字段名称
  for (int i = 0; i < this.dataGridView1.ColumnCount; i++)
  {
  strTitle += dataGridView1.Columns[i].HeaderText.ToString() + ",";
  }
  sw.WriteLine(strTitle.Substring(0, strTitle.Length - 1));
  //写内容
  string tempStr = "";
  for (int j = 0; j < this.dataGridView1.Rows.Count; j++)
  {
  for (int k = 0; k < this.dataGridView1.Columns.Count; k++)
  {
  tempStr += this.dataGridView1.Rows[j].Cells[k].Value.ToString() + ",";
  }
  sw.WriteLine(tempStr.Substring(0, tempStr.Length - 1));
  tempStr = "";
  }
  sw.Close();
  myStream.Close();
  MessageBox.Show("数据导出完成", "提示信息", MessageBoxButtons.OK, MessageBoxIcon.Information);
  }
  }
  //add by liuguichao@20110513
  else if (this.ckExcel.Checked)
  {
  dlg.Filter = "Excel文件 (*.xls)|*.xls";
  if (dlg.ShowDialog() == DialogResult.OK)
  {
  ExcelWriter writer = new ExcelWriter(dlg.FileName, "安徽边坡数据");
  string[] header = new string[dataGridView1.Columns.Count];
  Type[] colType = new Type[dataGridView1.Columns.Count];
  //生成字段名称
  for (int i = 0; i < dataGridView1.ColumnCount; i++)
  {
  header[i] = dataGridView1.Columns[i].HeaderText.ToString();
  colType[i] = typeof(System.String);
  }
  writer.WriteHeaderLine(header, colType);
  string[] dataLine = new string[dataGridView1.Columns.Count];
  for (int i = 0; i < this.dataGridView1.Rows.Count; i++)
  {
  for (int j = 0; j < this.dataGridView1.Columns.Count; j++)
  {
  dataLine[j] = this.dataGridView1.Rows[i].Cells[j].Value.ToString();
  }
  writer.WriteDataLine(dataLine);
  }
  writer.Save();
  MessageBox.Show("数据导出完成", "提示信息", MessageBoxButtons.OK, MessageBoxIcon.Information);