private void btnTK_Click(object sender, EventArgs e)
 {
     frmTraCuuPhong TK = new frmTraCuuPhong();
     TK.ShowDialog();
 }
 private void TraCuuPhongToolStripMenuItem_Click(object sender, EventArgs e)
 {
     frmTraCuuPhong child = new frmTraCuuPhong();
     child.MdiParent = this;
     child.Show();
 }