Flutter 在一个页面上自定义 AppBar

Question

我正在使用 AppBar 和 BottomNavigationBar 开发 Flutter 应用程序。这是代码:

class MainPage extends StatefulWidget {
  final MainModel model;

  MainPage(this.model);

  @override
  State<StatefulWidget> createState() {
    return _MainPageState();
  }
}

class _MainPageState extends State<MainPage> {
  int _selectedIndex = 0;

  Widget _openSelectedPage() {
    switch(_selectedIndex) {
      case 0:
        return HomePage(widget.model);
      case 1:
        return CapturePage(widget.model);
      case 2:
        return MealsPage(widget.model);
      default:
        return HomePage(widget.model);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('My App'),
      ),
      body: _openSelectedPage(),
      bottomNavigationBar: BottomNavigationBar(
        items: [
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            title: Text('Home'),
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.camera_alt),
            title: Text('Capture'),
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.format_list_bulleted),
            title: Text('Meals'),
          ),
        ],
        currentIndex: _selectedIndex,
        onTap: (int index) {
          setState(() {
            _selectedIndex = index;
          });
        }
      ),
    );
  }
}

如何在 MealsPage 上自定义 AppBar？如果我在 MealsPage 的 build 方法中添加另一个 Scaffold，那么它会创建两个 AppBar，这不是什么我想。我只想拥有一个 AppBar，即我在 MealsPage 中定义的那个。

Answer 1

class MainPage extends StatefulWidget {
  final MainModel model;

  MainPage(this.model);

  @override
  State<StatefulWidget> createState() {
    return _MainPageState();
  }
}

class _MainPageState extends State<MainPage> {
  int _selectedIndex = 0;

  Widget _openSelectedPage() {
    switch (_selectedIndex) {
      case 0:
        return HomePage(widget.model);
      case 1:
        return CapturePage(widget.model);
      case 2:
        return MealsPage(widget.model);
      default:
        return HomePage(widget.model);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: _selectedIndex == 2 ? null : AppBar(title: Text('My App')), 
      body: _openSelectedPage(),
      bottomNavigationBar: BottomNavigationBar(
        items: [
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            title: Text('Home'),
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.camera_alt),
            title: Text('Capture'),
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.format_list_bulleted),
            title: Text('Meals'),
          ),
        ],
        currentIndex: _selectedIndex,
        onTap: (int index) {
          setState(() {
            _selectedIndex = index;
          });
        },
      ),
    );
  }
}