asp.net导出txt文件

protected void btn3_Click(object sender, EventArgs e)  
    {  
        string sel = "select EX_Parent ,EX_PostCode ,EX_Address  from EnterInfo where EX_Mark like '%" + txtMark3.Text.Trim() + "%'";  
        DataTable dt = sqlHelper.ExectueTable(sel);  
//取datatable  

rtInfo.DataSource = dt;  
rtInfo.DataBind();  
rtInfo.Visible = true;  
string str = "";  
  
for (int i = 0; i < this.rtInfo.Items.Count; i++)  
{  
    Label labName = (Label)rtInfo.Items[i].FindControl("labName");  
    Label labCode = (Label)rtInfo.Items[i].FindControl("labCode");  
    Label labAddress = (Label)rtInfo.Items[i].FindControl("labAddress");  
  
    string vv = labName.Text;  
    str = str + (vv + ",");  
    string vv1 = labCode.Text;  
    str = str + (vv1 + ",");  
    string vv2 = labAddress.Text;  
    str = str + vv2;  
    str = str + ("\r\n");  
}  
  
Response.Clear();  
Response.Buffer = true;  
Response.Charset = "GB2312";  
Response.ContentEncoding = System.Text.Encoding.UTF8;  
//string val="online;filename=消费明细"+string.Format("{0:yyyyMMddHHmmss}",System.DateTime.Now)+".txt";  
Response.AddHeader("Content-Disposition", "attachment;filename=" + Server.UrlEncode("消费明细" + string.Format("{0:yyyyMMddHHmmss}", System.DateTime.Now) + ".txt"));  
//指定返回的是一个不能被客户端读取的流，必须被下载     
Response.ContentType = "text/plain";  
//把文件流发送到客户端     
Response.Write(str.ToString());  
//停止页面的执行     
Response.End();