C#程序发送POST请求数据中+号丢失解决方案

//如果需要POST数据   
if (!(parameters == null || parameters.Count == 0))
{
    StringBuilder buffer = new StringBuilder();
    int i = 0;
    foreach (string key in parameters.Keys)
    {
        if (i > 0)
        {
　　　　　　　//对有特殊字符的post内容进行转码
            buffer.AppendFormat("&{0}={1}", key, WebUtility.UrlEncode(parameters[key]));
        }
        else
        {
　　　　　　　//对有特殊字符的post内容进行转码
            buffer.AppendFormat("{0}={1}", key, WebUtility.UrlEncode(parameters[key]));
        }
        i++;
    }
    byte[] data = charset.GetBytes(buffer.ToString());
    using (Stream stream = request.GetRequestStream())
    {
        stream.Write(data, 0, data.Length);
    }
}