def registerViewType(self, cls, window=None):
        """
        Registers the inputed widget class as a potential view class.  If the \
        optional window argument is supplied, then the registerToWindow method \
        will be called for the class.
        
        :param          cls     | <subclass of XView>
                        window  | <QMainWindow> || <QDialog> || None
        """
        if ( not cls in self._viewTypes ):
            self._viewTypes.append(cls)
            
            if ( window ):
                cls.registerToWindow(window)