protected void btThem_Click(object sender, EventArgs e)
        {
            lbID.Visible = false;
            QlSachDbDataContext db = new QlSachDbDataContext();
            if (btThem.Text == "Thêm mới...")
            {
                tbID.Enabled = true;
                tbID.Text = "";
                tbHoten.Text = "";
                tbPass.Text = "";
                btSua.Enabled = false;
                btXoa.Enabled = false;
                rdAdmin.Checked = false;
                rdNormal.Checked = !rdAdmin.Checked;
                btThem.Text = "Thêm";
            }
            else
            {
                if (!db.DangNhaps.Any(p => p.TenDangNhap == tbID.Text))
                {
                    DangNhap dn = new DangNhap();
                    dn.TenDangNhap = tbID.Text;
                    dn.MatKhau = Encoding.MaHoa(Encoding.key,tbPass.Text);
                    dn.hoten = tbHoten.Text;
                    dn.Quyen = rdAdmin.Checked;
                    db.DangNhaps.InsertOnSubmit(dn);
                    db.SubmitChanges();
                    //System.Windows.Forms.MessageBox.Show("Thêm tài khoản mới thành công!");
                    Response.Write("<script>alert('Thêm tài khoản mới thành công!')</script>");

                    Response.Redirect(Request.RawUrl);
                    
                    //btThem.Text = "Thêm";
                    //drdID.DataSource = db.DangNhaps.Select(p => p.TenDangNhap);
                    //drdID.DataBind();
                    //drdID.SelectedValue = tbID.Text;

                    //ScriptManager.RegisterStartupScript(this.Page, this.Page.GetType(), "DoPostBack", "__doPostBack(sender, e)", true);

                }
                else
                {
                    lbID.Visible = true;
                }
            }
        }
 partial void UpdateDangNhap(DangNhap instance);
 partial void DeleteDangNhap(DangNhap instance);
 partial void InsertDangNhap(DangNhap instance);