private void btndangnhap_Click(object sender, EventArgs e) { GiaoVien gv = new GiaoVien(); gv.username = txttk.Text.Trim(); gv.pass = txtmk.Text.Trim(); if (GiaoVienController.DangNhap(gv) == null) { MessageBox.Show("Vui long kiem tra tai khoan va mat khau"); return; } gv = GiaoVienController.DangNhap(gv); frmMain mf = new frmMain(gv.IDGiaoVien, (int)gv.ad); mf.Show(); this.Hide(); }