How to Export DataGrid or GridView to Text

StringBuilder str = new StringBuilder();

for(int i=0;i<=ds.Tables[0].Rows.Count - 1; i++)
{
  for(int j=0;j<=ds.Tables[0].Columns.Count - 1; j++)
  {
      str.Append(ds.Tables[0].Rows[i][j].ToString());
  }

  str.Append("
");
}

Response.Clear();
Response.AddHeader("content-disposition", 
         "attachment;filename=FileName.txt");
Response.Charset = "";
Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.ContentType = "application/vnd.text";

System.IO.StringWriter stringWrite = new System.IO.StringWriter();
System.Web.UI.HtmlTextWriter htmlWrite = 
              new HtmlTextWriter(stringWrite);

Response.Write(str.ToString());
Response.End();