flutter - 在 Flutter 中访问对象数据

Question

我是 Flutter 的新手，正在尝试完成一些基础知识。我想从代码中多个位置的对象访问数据。

我很可能在 oo 代码中混淆了作用域或变量类型。到目前为止，我只使用 javascript 或 php 使用了基本的编码，并且从未玩过太多对象和东西。

请参阅下面的示例代码:

class _APPS extends State<APP>
    with SingleTickerProviderStateMixin {

  final pages = {
    "events": {
      "title": "Events",
      "icon": Icon(Icons.event),
      "page": EventsSite(),
    },
    "news": {
      "title": "News",
      "icon": Icon(Icons.message),
      "page": NewsSite(),
    },
    "favorites": {
      "title": "Favorites",
      "icon": Icon(Icons.favorite),
      "page": EventsSite(),
    },
    "profile": {
      "title": "Profile",
      "icon": Icon(Icons.account_circle),
      "page": EventsSite(),
    },
  };

  Widget build(BuildContext context) {
    return MaterialApp(
      home: Builder(
        builder: (context) => Scaffold(
          body: PageView(
            controller: _pageController,
            //physics: NeverScrollableScrollPhysics(),
            onPageChanged: _onPageChanged,
            children: [
              pages[0]['page'], <=== Here is what i'm trying to do
              NewsSite(),
              Icon(Icons.directions_bike),
            ],
          ),
          bottomNavigationBar: BottomNavigationBar(
            type: BottomNavigationBarType.fixed,
            showUnselectedLabels: false,
            backgroundColor: _colorBackgroundBright,
            unselectedItemColor: Colors.white,
            selectedItemColor: _colorHighlight,
            selectedLabelStyle: TextStyle(fontSize: 10.0),
            iconSize: 20,
            currentIndex: _selectedIndex,
            onTap: _onItemTapped,
            items: const <BottomNavigationBarItem>[
              BottomNavigationBarItem(
                icon: Icon(pages['Events']['icon']), <=== Here is what i'm trying to do
                title: Text(pages[0]['title']), <=== Here is what i'm trying to do
              ),
              BottomNavigationBarItem(
                icon: Icon(Icons.message),
                title: Text('News'),
              ),
              BottomNavigationBarItem(
                icon: Icon(Icons.favorite),
                title: Text('Favorites'),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

Answer 1

您需要访问您的 Map适本地。

而不是 pages[0]或 pages['Events'] ，您要指定正确的 key :

pages['events']

映射键区分大小写，因为它们使用 equals operator .

您无法访问 Map创建 const 时.所以删除 const在 const <BottomNavigationBarItem>[ :

<BottomNavigationBarItem>[
  ...
]

此外，对于图标，您需要使用 pages['events']['icon'] .