根据城市获取天气预报

public void GetWetheaerByCity(string cityName) {
string city = cityName;
string mycity = HttpUtility.UrlEncode(city, System.Text.Encoding.GetEncoding("GB2312"));
System.Net.HttpWebRequest request = (System.Net.HttpWebRequest)System.Net.WebRequest.Create("http://www.sina.com/index.php?city=" + cityName);
//HttpWebRequest 对象 获取GetResponse 转换成HttpWebResponse
System.Net.HttpWebResponse response = request.GetResponse() as System.Net.HttpWebResponse;
//通过HttpWebResponse response.GetResponseStream()获取输出流
Stream str = response.GetResponseStream();
StreamReader reader = new StreamReader(str, System.Text.Encoding.GetEncoding("GB2312"));
string weathhtml = reader.ReadToEnd();
str.Close();
reader.Close();