private void bánHàngToolStripMenuItem_Click(object sender, EventArgs e)
{
if (Application.OpenForms["frm_hoadon"] == null)
{
frm_hoadon tthd = new frm_hoadon();
tthd.MdiParent = this;
tthd.Show();
}
else
{
Application.OpenForms["frm_hoadon"].Activate();
}
}
public Lopdungchung(GUI.frm_hoadon f)
{
frmhd = f;
}