private void TtDonVi_Click(object sender, EventArgs e)
 {
     if (ttDonVi == null || ttDonVi.IsDisposed)
     {
         ttDonVi = new FrmQuanLyDonVi();
     }
     ttDonVi.MdiParent = this;
     ttDonVi.Show(dockPanelMain);
 }
 //Quan ly phong ban
 private void ttDonVitoolStripButton_Click(object sender, EventArgs e)
 {
     if (ttDonVi == null || ttDonVi.IsDisposed)
     {
         ttDonVi = new FrmQuanLyDonVi();
     }
     ttDonVi.MdiParent = this;
     ttDonVi.Show(dockPanelMain);
     this.Activate();
 }