WebClient模拟发送Post请求方法：
/// <summary>
/// 模拟post请求
/// </summary>
/// <param name="Url"></param>
/// <param name="postDataStr"></param>
/// <returns></returns>
private string HttpPost(string Url, string postDataStr)
{
byte[] bytes = Encoding.UTF8.GetBytes(postDataStr);
WebClient client = new WebClient();
client.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
client.Headers.Add("ContentLength", postDataStr.Length.ToString());
byte[] responseData = client.UploadData(Url, "POST", bytes);
string retString = Encoding.UTF8.GetString(responseData);
return retString;
}
调用方法：
string postDataStr = "userId=" + userId + "&sig=" + sigStr;
string jsonStr = HttpPost("http://www.xx/query.json", postDataStr); //返回utf8的JSON