C# 写入html 乱码问题 - .NET技术 / C#

string fileName = Request.PhysicalApplicationPath.ToString() + this.filepath.Replace(@"\", @"\\") + @"mm\" + this.ddlType.SelectedValue + ".htm";//路径
  FileInfo info = new FileInfo(fileName);
  if (info.Exists)//修改
  {
  StreamWriter writer = info.CreateText();
  writer.WriteLine(this.txtContent.Text.Trim());
  writer.Close();
  }
  else//不存在时新建
  {
  StreamWriter writer2 = File.CreateText(fileName);
  writer2.WriteLine(this.txtContent.Text.Trim());
  writer2.Close();
  }
  this.Page.RegisterStartupScript("alert", "<script language=javascript>alert('操作完成！');</script>");

最后插入里面中文都是乱码
  我又把上面修改了一下
 string fileName = Request.PhysicalApplicationPath.ToString() + this.filepath.Replace(@"\", @"\\") + @"mm\" + this.ddlType.SelectedValue + ".htm";
  FileInfo info = new FileInfo(fileName);
  if (info.Exists)
  {
  StreamWriter writer = info.CreateText();
  writer.WriteLine(this.txt