public PrincipalForm(LoginForm lf)
 {
     this.lform = lf;
     InitializeComponent();
     Listar();
 }
 private void cerrarSesiónToolStripMenuItem_Click(object sender, EventArgs e)
 {
     this.Dispose();
     LoginForm login = new LoginForm();
     login.ShowDialog();
     this.Close();
 }
 private void menuArchivoCerrarSesion_Click(object sender, EventArgs e)
 {
     this.Dispose();
     LoginForm login = new LoginForm();
     login.ShowDialog();
     this.Close();
 }