private void pOPToolStripMenuItem_Click(object sender, EventArgs e) { if (popFrm == null) { popFrm = new PopForm(); popFrm.WindowState = FormWindowState.Maximized; popFrm.MdiParent = this; popFrm.Show(); } else { foreach (Form frm in Application.OpenForms) { if (frm is PopForm) { frm.Activate(); } } } }