Motivation

Flutter provides a nice widget for making bottom navigation UI but they don't support navigation and transition. Handling the back button on Android and adding transitions to a bottom navigation widget is not that easy. Just like the TabBarView and TabBarController, we need a set of widgets and classes that will help implement bottom navigation while being UI agnostics. This package provides a set of widgets and a controller to make it easy to implement back button handling and transitions.

Demo

Cross Fade

Fade Through (https://material.io/design/motion/the-motion-system.html#fade-through)

Getting Started

If you have ever worked with the TabBarView widget, working with the BottomNavigationView widget would be easier. The BottomNavigationView widget works almost the same and it follows the same semantics.

First of all, we are going to declare the BottomNavigationController. It takes the SingleTickerProviderMixin as a required argument just like the TabBarController. Don't forget to dispose it in the dispose() method.

class Home extends StatefulWidget {
  const Home({Key? key}) : super(key: key);

  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> with SingleTickerProviderStateMixin {
  late final BottomNavigationController _controller;

  @override
  void initState() {
    super.initState();
    _controller = BottomNavigationController(vsync: this);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

Next, we are going to use the BottomNavigationView and BottomNavigationIndexedBuilder widget. Both take the BottomNavigationController as the controller property. You must give the same instance of the BottomNavigationController in order for it to work properly.

The BottomNavigationView takes screen widgets as the children property. The widgets will become the screen of each bottom navigation. You can give it a Navigator widget to make nested navigation.

BottomNavigationView(
  controller: _controller,
  transitionType: BottomNavigationTransitionType.none,
  children: const [
    ColorScreen(color: Colors.red, name: 'Red'),
    ColorScreen(color: Colors.amber, name: 'Amber'),
    ColorScreen(color: Colors.yellow, name: 'Yellow'),
    ColorScreen(color: Colors.green, name: 'Green'),
    ColorScreen(color: Colors.blue, name: 'Blue'),
  ],
)

The BottomNavigationIndexedBuilder has the builder property. The builder function will be called whenever the controller detects a navigation index change and it provides the changed index as the second argument. Here, you can return any kind of customized bottom navigation widget. It's completely UI agnostics and it works well with any bottom navigation widget packages.

BottomNavigationIndexedBuilder(
  controller: _controller,
  builder: (context, index, child) {
    return BottomNavigationBar(
      currentIndex: index,
      onTap: (index) {
        _controller.goTo(index);
      },
      type: BottomNavigationBarType.fixed,
      items: const [
        BottomNavigationBarItem(label: 'Red', icon: Icon(Icons.home)),
        BottomNavigationBarItem(label: 'Amber', icon: Icon(Icons.home)),
        BottomNavigationBarItem(label: 'Yellow', icon: Icon(Icons.home)),
        BottomNavigationBarItem(label: 'Green', icon: Icon(Icons.home)),
        BottomNavigationBarItem(label: 'Blue', icon: Icon(Icons.home)),
      ],
    );
  },
),

Once you build up your UI, you are ready to call the goTo() and goBack() functions on the BottomNavigationController. Call the goTo() function in the BottomNavigationBar and the goBack() function on the WillPopScope widget to handle the back button on Android. If you want to change the transition animation, specify the transitionType with one of the BottomNavigationTransitionType enum values. It has the fadeInOut and fadeThrough value. You can see how it looks on the demo.

The package also provides the DefaultBottomNavigationController just like the DefaultTabBarController.

class Home extends StatelessWidget {
  const Home({ Key? key }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return DefaultBottomNavigationController(child: ...)
  }
}

Take a look at the complete code below.

class _HomeScreenState extends State<HomeScreen> with SingleTickerProviderStateMixin {
  late final BottomNavigationController _controller;

  @override
  void initState() {
    super.initState();
    _controller = BottomNavigationController(vsync: this);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () async {
        _controller.goBack();
        return false;
      },
      child: Scaffold(
        body: BottomNavigationView(
          controller: _controller,
          transitionType: BottomNavigationTransitionType.none,
          children: const [
            ColorScreen(color: Colors.red, name: 'Red'),
            ColorScreen(color: Colors.amber, name: 'Amber'),
            ColorScreen(color: Colors.yellow, name: 'Yellow'),
            ColorScreen(color: Colors.green, name: 'Green'),
            ColorScreen(color: Colors.blue, name: 'Blue'),
          ],
        ),
        bottomNavigationBar: BottomNavigationIndexedBuilder(
          controller: _controller,
          builder: (context, index, child) {
            return BottomNavigationBar(
              currentIndex: index,
              onTap: (index) {
                _controller.goTo(index);
              },
              type: BottomNavigationBarType.fixed,
              items: const [
                BottomNavigationBarItem(label: 'Red', icon: Icon(Icons.home)),
                BottomNavigationBarItem(label: 'Amber', icon: Icon(Icons.home)),
                BottomNavigationBarItem(label: 'Yellow', icon: Icon(Icons.home)),
                BottomNavigationBarItem(label: 'Green', icon: Icon(Icons.home)),
                BottomNavigationBarItem(label: 'Blue', icon: Icon(Icons.home)),
              ],
            );
          },
        ),
      ),
    );
  }
}

Additional Information

How does this package remember the navigation history?

It works exactly the same as Youtube or Instagram. If you are an Android user, play with Youtube or Instagram with the back button and see how they implement their navigation. The package will remember the index you visited and store it in a list. But once you visit the same index that you already visited, that index will be dropped and there will be no duplicates. This prevents the history to be grown infinitely.