private void onCloseWindow(ExmWindow target)
    {
        ExmWindowChange change = ChangeDispatcher <ExmWindowChange> .GetChange();

        change.target = target;
        dispatcher.dispatchChange(change, ExmWindowChangeType.WINDOW_CLOSED);

        //...
    }
    public void openWindow(string title, string message)
    {
        ExmWindow w = createWindow();

        w.setData(title, message, onCloseWindow);

        //...

        ExmWindowChange change = ChangeDispatcher <ExmWindowChange> .GetChange();

        change.target = w;
        dispatcher.dispatchChange(change, ExmWindowChangeType.WINDOW_OPENED);
    }
 override protected void executeClear()
 {
     target = null;
 }