WebClient发送POST请求

string postData = "client_id="+ Sina.APP_ID +"&client_secret="+ Sina.APP_KEY +"&grant_type=authorization_code&redirect_uri="+ Sina.RedirectUrl +"&code="+code;

byte[] bytes = Encoding.UTF8.GetBytes(postData);

WebClient client = new WebClient();

client.Headers.Add("Content-Type", "application/x-www-form-urlencoded");

client.Headers.Add("ContentLength", postData.Length.ToString());

byte[] responseData = client.UploadData("https://api.weibo.com/oauth2/access_token", "POST", bytes);