Single Instance Form in a MDI application

This example contains the code to manage the menu of open forms (standard Windows menu). When created, each mdi-child gets a menu item and event handler through which this element is removed from the menu when the corresponding form is closed.

private void ShowOrCreateMdiChild(Type formType) {
   foreach (Form frm in MdiChildren) {
      if (frm.GetType() == formType) {
         frm.Select();
         return;
      }
   }
   Form f = Activator.CreateInstance(formType) as Form;
   ShowMdiChild(f);
}

private void ShowMdiChild(Form form) {
   ToolStripMenuItem aWindowMenuItem = 
     new ToolStripMenuItem(form.Text, Bitmap.FromHicon(form.Icon.Handle));
   aWindowMenuItem.Tag = form;
   aWindowMenuItem.Click += new EventHandler(aWindowMenuItem_Click);
   m_windowsMenu.DropDownItems.Add(aWindowMenuItem);
   //m_windowsMenu - menu containing all MDI children
   form.FormClosed += new FormClosedEventHandler(mdiForm_FormClosed);
   form.MdiParent = this;
   form.Location = new Point(0, 0);
   form.Size = new Size(this.ClientSize.Width - 30, 
        this.ClientSize.Height - this.statusStrip1.Height - 30);
   form.StartPosition = FormStartPosition.Manual;
   form.Show();
   form.Select();
}

void mdiForm_FormClosed(object sender, FormClosedEventArgs e) {
   ToolStripItem itemToRemove = null;
   foreach (ToolStripItem mnu in m_windowsMenu.DropDownItems)
      if (mnu.Tag == sender) {
         itemToRemove = mnu;
         break;
      }
   if (itemToRemove != null)
      m_windowsMenu.DropDownItems.Remove(itemToRemove);
}

void aWindowMenuItem_Click(object sender, EventArgs e) {
   ToolStripMenuItem mnu = sender as ToolStripMenuItem;
   Form f = mnu.Tag as Form;
   if (f != null) {
      f.BringToFront();
      f.Focus();
   }
}