string username = txtusername.Text;
        string password = txtpassword.Text;

        DataTable dt=user.UserLogin(username, MySecurity.Pw_Md5(password));
        if (dt.Rows.Count == 1)
        {
            DataRow R = dt.Rows[0];
            Session["usin_id"] = R["usin_id"].ToString();
            Session["usin_nickname"] = R["usin_nickname"].ToString();
            //txtNickname是一个Label
            txtNickname.Text = Session["usin_nickname"].ToString();
            Response.Redirect(Request.Url.ToString());
        }
        else
        {
            MyScript.ShowAndRedirect(this.Page, "用户名或密码错误", Request.Url.ToString());
        }