ToolStripDropDown.Closing Event

// This method handles the Closing event. The ToolStripDropDown 
// control is not allowed to close unless the Done menu item 
// is clicked or the Close method is called explicitly. 
// The Done menu item is enabled only after both of the other 
// menu items have been selected. 
private void contextMenuStrip_Closing(
    object sender, 
    ToolStripDropDownClosingEventArgs e)
{
    if (e.CloseReason != ToolStripDropDownCloseReason.CloseCalled)
    {
        if (subItem1ToolStripMenuItem.Checked &&
            subItem2ToolStripMenuItem.Checked &&
            doneToolStripMenuItem.Enabled)
        {
            // Reset the state of menu items.
            subItem1ToolStripMenuItem.Checked = false;
            subItem2ToolStripMenuItem.Checked = false;
            doneToolStripMenuItem.Enabled = false;

            // Allow the ToolStripDropDown to close. 
            // Don't cancel the Close operation.
            e.Cancel = false;
        }
        else
        {
            // Cancel the Close operation to keep the menu open.
            e.Cancel = true;
            this.toolStripStatusLabel1.Text = "Close canceled";
        }
    }
}