private void librosToolStripMenuItem_Click(object sender, EventArgs e)
        {
            FormLibros frm = FormLibros.ObtenerInstancia();

            frm.MdiParent = this;
            frm.Show();
            frm.BringToFront();
        }
 public static FormLibros ObtenerInstancia()
 {
     if (instancia == null)
     {
         instancia             = new FormLibros();
         instancia.FormClosed += new FormClosedEventHandler(reset);//SOLO PARA FORMULARIOS
     }
     return(instancia);
 }
 private static void reset(object sender, FormClosedEventArgs e)//SOLO PARA FORMULARIOS
 {
     instancia = null;
 }