如何模拟登陆?当登陆按钮是图片？保存session。
http://www.xxx.com/login/login_index.jsp
要模拟登陆的网址。

<form name="formreg" id="formreg" method="post" target="UserCenter" style="float:left;margin:0;padding:0;" onSubmit="return loginchk();">



    <div class="nrikey">



      <ul>



        <li>用户名</li>



        <li class="nname01">



          <input name="us" id="us" type="text" class="nname" />



        </li>



      </ul>



      <ul>



        <li>密　码</li>



        <li class="nname01">



          <input name="_pwd" id="_pwd" type="password" class="nname" />



        </li>



      </ul>



    </div>



    <div class="namebot"><img src="/images/index2011new03qt_19.jpg" style="cursor: pointer;" width="50" height="44" onClick="if(document.formreg.onsubmit()!=false){document.formreg.submit();setTimeout('window.location.reload()',3000);}"/></div>

    </form>

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上面是要模拟的网站代码

 class PostGetWebRequest

    {

        private string userName;

        private string password;

        private string submit;

        private string loginUrl;

        private string locationUrl;

        private CookieContainer myCookieContainer;

        private HttpWebRequest request;

        private HttpWebResponse response;

        private Stream stream;

        private StreamReader streamReader;

        private string src = "";

        private string postData;

        private string htmlUserName;

        private string htmlPassword;

        private string htmlSubmit;



        #region 类的成员 类的成员

        public string UserName

        {

            get { return userName; }

            set { userName =&nbs