private void btnDN_Click(object sender, EventArgs e) { NguoiDungBUS nguoiDungBus = new NguoiDungBUS(); if (nguoiDungBus.KTraDangNhap(txt_Username.Text, txt_MatKhau.Text)) { Program.Username = txt_Username.Text; this.Close(); th = new Thread(OpenForm); th.SetApartmentState(ApartmentState.STA); th.Start(); } else { MessageBox.Show("Đăng nhập thất bại"); } }