private void mDI1ToolStripMenuItem_Click(object sender, EventArgs e)
{
if (md1 == null)
{
md1 = new frm_mdi1();
md1.MdiParent = this;
md1.FormClosed += new FormClosedEventHandler(md1_closed);
md1.Show();
}
else
{
md1.Activate();
}
}
public void md1_closed(object sender, FormClosedEventArgs e)
{
md1 = null;
}
