public void Popup(IntelliSenseContext ctx) {
     Debug.Assert(_context == null);
     _context = ctx;
     AdjustListBox();
     this.Show(_context.OwnerControl, ToControlPoint(ctx.CommandStartPoint));
     _listBox.Focus();
     _status = ComplementStatus.Selecting;
 }
        //ここまで

        private void Exit() {
            Debug.WriteLineIf(DebugOpt.IntelliSense, "Exit");
            Debug.Assert(_context != null);

            ComplementStatus s = _status;
            _status = ComplementStatus.Exiting;
            this.Hide();
            _context = null;
            _status = s;
        }