/// <summary>
        /// 登陆：检查
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param> 

private void btnLogin_Click(object sender, EventArgs e)
        {
            //第7章第2题的思路;
            string sql = string.Format("select count(*)form users where id={0} and loginPwd='{1}'",txtLoginId.Text.Trim(),txtLoginPwd.Text.Trim());
            //找出你的登录成功的代码
            //int count=Convert.ToInt32(comm.ExecuteScalar()); 第1行第1列的值，Object类型；需要强转
            //UserHelper类，记录当前登录的QQ号.
            //if (count > 0)
            //{
            //    UserHelper.loginId = int.Parse(txtLoginId.Text.Trim()); //则将当前QQ号。
            UserHelper.loginId = int.Parse(txtLoginId.Text.Trim());
                 //new 主窗体;
                DBHelper.conn.Close();

                MainForm mf = new MainForm();

                mf.Show();
                this.Visible = false;
            //}
            

            //如果登录成功，则将成功的QQ号码，存放到UserHelper的id里面
           
        }
        //窗体加载事件;
        private void LoginForm_Load(object sender, EventArgs e)
        {
            skinEngine1.SkinFile = "skins\\MSN.ssk";
            //皮肤控件的皮肤=文件路径
        }
        //皮肤下拉框控件，选项改变事件;
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            skinEngine1.SkinFile = "skins\\" + comboBox1.Text;
        }