UI层：
    protected void Page_Load(object sender, EventArgs e)
    { 
}
    protected void Button1_Click(object sender, EventArgs e) //两参按钮
    {
        string username = TextBox1.Text.Trim();
        string userpwd = TextBox2.Text.Trim();
        DataTable dt = new P_AdminManager().SelectAdmin(username, userpwd);
        int i = dt.Rows.Count;
        if (i > 0)
        {
            TextBox1.Text = Convert.ToString(i);
            TextBox2.Text = "登录成功";
        }
        else
        { 
            TextBox1.Text = Convert.ToString(i); 
            TextBox2.Text = "登录失败";
        }
    protected void Button2_Click(object sender, EventArgs e) //一参按钮
    {
        string username = TextBox1.Text.Trim();
        string userpwd = TextBox2.Text.Trim();
        DataTable dt = new P_AdminManager().SelectByUser(username);// 
        int i = dt.Rows.Count;
        if (i > 0)
        {
            TextBox1.Text = Convert.ToString(i);
            TextBox2.Text = "登录成功";
        }
        else
        { 
            TextBox1.Text = Convert.ToString(i); 
            TextBox2.Text = "登录失败";
        }
    }
}

BLL层：
    public class P_AdminManager
    {
        private P_AdminDAO P_dao = null;
        public P_AdminManager()
        {
            P_dao = new P_AdminDAO();
        }
        public DataTable SelectByUser(string un) //单参
        {
            return P_dao.SelectByUser(un);
        }
        public DataTable  SelectAdmin(string username, string userpwd)//双参
        {
            return P_dao.SelectAdmin(username,userpwd);
        } 
}

DLL层：
    public class P_AdminDAO
    {
        private SQLHelper sqlhelper;
        public P_AdminDAO()
        {
            sqlhelper = new SQLHelper();
        }
//单参――――――――――――――――――――――――
        public DataTable SelectByUser(string un) 
        {
            DataTable dt = new DataTable();
            string cmdText = "select * from P_Admin where P_adminame=@P_adminame";
            SqlParameter[] para = new SqlParameter[] { 
                new SqlParameter("@P_adminame", un) };
            dt = sqlhelper.ExecuteQuery(cmdText, para, CommandType.Text);
            return dt;
        }
//双参―――――――――――――――――――――――――――
        public DataTable  SelectAdmin(string username, string userpwd)
        {
            DataTable dt = new DataTable();
            string cmdText = "select * from P_Admin where  P_adminame=@P_adminame and P_adminpwd=@P_adminpwd";//
            SqlParameter[] paras = new SqlParameter[]{
            new SqlParameter("@P_adminame",username),
            new SqlParameter("@P_adminpwd",userpwd)};//            
            dt = sqlhelper.ExecuteQuery(cmdText, paras, CommandType.Text);
            return dt;
        }
}
Sqlhelper类：
    public class SQLHelper
    {
        private SqlConnection conn = null;
        private SqlCommand cmd = null;
        private SqlDataReader sdr = null;
        public SQLHelper()
        {
            string connStr = ConfigurationManager.ConnectionStrings["connStr"].ConnectionString;                             
            conn = new SqlConnection(connStr);
        }
        public SqlConnection GetConn()
        {
            if (conn.State == ConnectionState.Closed)
            { conn.Open(); }
            return conn;
   }

//带参查询
        public DataTable ExecuteQuery(string cmdText, SqlParameter[] paras, CommandType ct)
        {
            DataTable dt = new DataTable();
            cmd = new SqlCommand(cmdText, GetConn());
            cmd.CommandType = ct;
            cmd.Parameters.AddRange(paras);
            using (sdr = cmd.ExecuteReader(CommandBehavior.CloseConnection))
            {
                dt.Load(sdr);
            }
            re