C# winform post 请求指定 url

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;

namespace Tt.KD100.Initiative.WinService
{
  /// <summary>
  /// 请求信息帮助
  /// </summary>
  public class HttpHelper
  {
    /// <summary>
    /// post 请求指定地址返回响应数据
    /// </summary>
    /// <param name="url">请求地址</param>
    /// <param name="postData">请求数据</param>
    /// <param name="timeout">请求超时时间（毫秒）</param>
    /// <param name="requestCoding">请求编码</param>
    /// <param name="responseCoding">响应编码</param>
    /// <returns></returns>
    public string PostRequest(string url, Dictionary<string, string> postData, int timeout,Encoding requestCoding, Encoding responseCoding)
    {
      string postStr = string.Empty;
      if (postData!=null)
      {
        postData.All(o =>
                       {
                         if (string.IsNullOrEmpty(postStr))
                           postStr = string.Format("{0}={1}", o.Key, o.Value);
                         else
                           postStr += string.Format("&{0}={1}", o.Key, o.Value);

                         return true;
                       });
      }
      return PostRequest(url, postStr,timeout, requestCoding, responseCoding);
    }
    /// <summary>
    /// post 请求指定地址返回响应数据
    /// </summary>
    /// <param name="url">请求地址</param>
    /// <param name="postData">请求数据</param>
    /// <param name="timeout">请求超时时间（毫秒）</param>
    /// <param name="requestCoding">请求编码</param>
    /// <param name="responseCoding">响应编码</param>
    /// <returns></returns>
    public string PostRequest(string url, string postData,int timeout, Encoding requestCoding,Encoding responseCoding)
    {
      string postUrl = VerifyUrl(url);
      try
      {
        //写入POSTDATE里
        byte[] byteArray = requestCoding.GetBytes(postData);
        HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(new Uri(postUrl));
        webRequest.Method = "POST";
        webRequest.Timeout = timeout;
        webRequest.ContentType = "application/x-www-form-urlencoded";
        webRequest.ContentLength = byteArray.Length;
        Stream newStream = webRequest.GetRequestStream();
        newStream.Write(byteArray, 0, byteArray.Length);
        newStream.Close();
        //接收返回信息：
        HttpWebResponse response = (HttpWebResponse)webRequest.GetResponse();
        StreamReader php = new StreamReader(response.GetResponseStream(), responseCoding);
        string result = php.ReadToEnd();
        return result;
      }
      catch (Exception ex)
      {
        Grass.Log.ExceptionsStack.RegisterError(ex);
        return string.Empty;
      }
    }
    /// <summary>
    /// 验证URL
    /// </summary>
    /// <param name="url">待验证 URL</param>
    /// <returns></returns>
   private string VerifyUrl(string url)
    {
      if(string.IsNullOrEmpty(url))
        throw new Exception("URL 地址不可以为空！");

      if (url.StartsWith("http://", StringComparison.CurrentCultureIgnoreCase))
        return url;

      return string.Format("http://{1}", url);
    }
  }
}