在NavigationDrawer（胶子移动）图标不可见

Question

我使用NavigationDrawer在我的应用中创建了导航抽屉 在我的NavigationDrawer版本的viewitem中看不到该图标 这是代码......

Node getNavigation()
{

NavigationDrawer drawer=(NavigationDrawer)getDrawer();
NavigationDrawer.Header header =new NavigationDrawer.Header(
"Mobile App","Navigate through ...",
                new Avatar(21, new Image(getClass().getResourceAsStream("/icon.png"))));
        drawer.setHeader(header);

        final Item primaryItem = new ViewItem("Primary", MaterialDesignIcon.HOME.graphic(), PRIMARY_VIEW, ViewStackPolicy.SKIP);

        final Item secondaryItem = new ViewItem("Secondary", MaterialDesignIcon.DASHBOARD.graphic(), SECONDARY_VIEW);

        drawer.getItems().addAll(primaryItem, secondaryItem);

    return drawer;
}

以下是ScreenShot ......