Hide bottom navigation bar on scroll down and vice versa

问题

I have a list in the body and bottom navigation bar. I want to hide bottom navigation bar with a slide down animation when the posts list is scrolled down and visible with a slide up animation when scrolled up. How to do it?

回答1:

Here is the code.

void main() => runApp(MaterialApp(home: Scaffold(body: MyApp())));

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  ScrollController _scrollController;
  double _containerMaxHeight = 56, _offset, _delta = 0, _oldOffset = 0;

  @override
  void initState() {
    super.initState();
    _offset = 0;
    _scrollController = ScrollController()
      ..addListener(() {
        setState(() {
          double offset = _scrollController.offset;
          _delta += (offset - _oldOffset);
          if (_delta > _containerMaxHeight)
            _delta = _containerMaxHeight;
          else if (_delta < 0) _delta = 0;
          _oldOffset = offset;
          _offset = -_delta;
        });
      });
  }

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(
      builder: (context, constraints) {
        return Stack(
          alignment: Alignment.bottomCenter,
          children: <Widget>[
            ListView.builder(
              physics: ClampingScrollPhysics(),
              controller: _scrollController,
              itemCount: 20,
              itemBuilder: (context, index) => ListTile(title: Text(index.toString())),
            ),
            Positioned(
              bottom: _offset,
              width: constraints.maxWidth,
              child: Container(
                width: double.infinity,
                height: _containerMaxHeight,
                color: Colors.grey[300],
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: <Widget>[
                    _buildItem(Icons.home, "Home"),
                    _buildItem(Icons.blur_circular, "Collection"),
                    _buildItem(Icons.supervised_user_circle, "Community"),
                    _buildItem(Icons.notifications, "Notifications"),
                  ],
                ),
              ),
            ),
          ],
        );
      },
    );
  }

  Widget _buildItem(IconData icon, String title) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Icon(icon, size: 28),
        Text(title, style: TextStyle(fontSize: 10)),
      ],
    );
  }
}

Note: I tried bottomNavigationBar but things were not working as expected so I created kind of my own bottom navigation bar and you can modify the code further for your use.

Screenshot

回答2:

Working code with BottomNavigationBar.

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  ScrollController _hideBottomNavController;

  bool _isVisible;

  @override
  initState() {
    super.initState();
    _isVisible = true;
    _hideBottomNavController = ScrollController();
    _hideBottomNavController.addListener(
      () {
        if (_hideBottomNavController.position.userScrollDirection ==
            ScrollDirection.reverse) {
          if (_isVisible)
            setState(() {
              _isVisible = false;
            });
        }
        if (_hideBottomNavController.position.userScrollDirection ==
            ScrollDirection.forward) {
          if (!_isVisible)
            setState(() {
              _isVisible = true;
            });
        }
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: CustomScrollView(
          controller: _hideBottomNavController,
          shrinkWrap: true,
          slivers: <Widget>[
            SliverPadding(
              padding: const EdgeInsets.all(10.0),
              sliver: SliverList(
                delegate: SliverChildBuilderDelegate(
                  (context, index) => _getItem(context),
                  childCount: 20,
                ),
              ),
            ),
          ],
        ),
      ),
      bottomNavigationBar: AnimatedContainer(
        duration: Duration(milliseconds: 500),
        height: _isVisible ? 56.0 : 0.0,
        child: Wrap(
          children: <Widget>[
            BottomNavigationBar(
              type: BottomNavigationBarType.fixed,
              backgroundColor: Colors.blue,
              fixedColor: Colors.white,
              unselectedItemColor: Colors.white,
              items: [
                BottomNavigationBarItem(
                  icon: Icon(Icons.home),
                  title: Text('Home'),
                ),
                BottomNavigationBarItem(
                  icon: Icon(Icons.card_giftcard),
                  title: Text('Offers'),
                ),
                BottomNavigationBarItem(
                  icon: Icon(Icons.account_box),
                  title: Text('Account'),
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }

  _getItem(BuildContext context) {
    return Card(
      elevation: 3,
      margin: EdgeInsets.all(8),
      child: Row(
        children: <Widget>[
          Expanded(
            child: Container(
              padding: EdgeInsets.all(8),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: <Widget>[
                  Padding(
                    padding: const EdgeInsets.all(8.0),
                    child: Text(
                      'Item',
                      style:
                          TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
                    ),
                  )
                ],
              ),
            ),
          ),
        ],
      ),
    );
  }
}

Working Model

来源：https://stackoverflow.com/questions/54414268/hide-bottom-navigation-bar-on-scroll-down-and-vice-versa