private void buttonItem3_Click(object sender, EventArgs e)
 {
     if (ChucVufrm == null || ChucVufrm.IsDisposed)
     {
         ChucVufrm           = new frmChucVu();
         ChucVufrm.MdiParent = this;
         ChucVufrm.Show();
     }
     else
     {
         ChucVufrm.Activate();
     }
 }
        private void btnChucVu_Click(object sender, EventArgs e)
        {
            frmChucVu CV = new frmChucVu();

            CV.ShowDialog();
        }