private void registerListeners() {
        widthProperty().addListener(observable -> resize());
        heightProperty().addListener(observable -> resize());
        symbolType.addListener(observable -> {
            setId(getSymbolType().STYLE_CLASS);
            resize();
        });
        color.addListener(observable -> setStyle("-symbol-color: " + Util.colorToCss(getColor()) + ";"));
    }