四控件:Textbox,button,dropdownlist,Label调用sina接口，查询天气
using System.Net;
using System.IO;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e) 点击 DropDownList写代码
{
string weacherhtml = String.Empty;
string mycity = System.Web.HttpUtility.UrlEncode(DropDownList1.SelectedItem.Text, System.Text.UnicodeEncoding.GetEncoding("GB2312"));
HttpWebRequest webrt = (HttpWebRequest)WebRequest.Create("http://php.weather.sina.com.cn/search.php?city=" + mycity);
HttpWebResponse webrs = (HttpWebResponse)webrt.GetResponse();
Stream stream = webrs.GetResponseStream();
StreamReader srm = new StreamReader(stream, System.Text.Encoding.Default);
weacherhtml = srm.ReadToEnd();
int x = weacherhtml.IndexOf("今日");
int y = weacherhtml.IndexOf("分区浏览");
weacherhtml = weacherhtml.Substring(x,y-x);

srm.Close();
webrs.Close();
Response.Write(weacherhtml);
Label1.Text = weacherhtml;

}
protected void Button1_Click(object sender, EventArgs e) 点击button写代码
{
string weacherhtml = String.Empty;
string mycity = System.Web.HttpUtility.UrlEncode(TextBox1.Text, System.Text.UnicodeEncoding.GetEncoding("GB2312"));
HttpWebRequest webrt = (HttpWebRequest)WebRequest.Create("http://php.weather.sina.com.cn/search.php?city=" + mycity);
HttpWebResponse webrs = (HttpWebResponse)webrt.GetResponse();
Stream stream = webrs.GetResponseStream();
StreamReader srm = new StreamReader(stream, System.Text.Encoding.Default);
weacherhtml = srm.ReadToEnd();
int x = weacherhtml.IndexOf("今日");
int y = weacherhtml.IndexOf("分区浏览");
weacherhtml = weacherhtml.Substring(x, y - x);

srm.Close();
webrs.Close();
Response.Write(weacherhtml);