我真的很喜欢 BLoC 模式，我正在努力理解它。但我似乎无法弄清楚它应该如何应用于 BottomNavigationBar。

由于 setState()，制作导航页面列表并在导航栏点击事件上设置当前索引会导致整个应用重绘。

我可以使用 Navigator 来显示点击的导航页面而不丢失导航栏吗？

有没有人将 BLoC 模式与 BottomNavigationBar 一起使用？我该怎么做呢 ？我很想看看示例代码。

最佳答案

我终于明白了。我将整个代码放在这里是为了帮助其他人。

首先阅读 didier boelens 的这篇精彩文章:https://www.didierboelens.com/2018/08/reactive-programming---streams---bloc/

使用他的区 block 提供者和基础区 block 创建区 block 。我的是这样的:

import 'dart:async';
import 'bloc_provider.dart';
import 'package:rxdart/rxdart.dart';

class NewsfeedBloc implements BlocBase {
  BehaviorSubject<int> _ctrl = new BehaviorSubject<int>();

  NewsfeedBloc(
      // listen _ctrl event and do other business logic
  );

  void dispose() {
    _ctrl.close();
  }
}

然后创建将使用 bloc 的页面:

import 'package:flutter/material.dart';
import '../blocs/newsfeed_bloc.dart';
import '../blocs/bloc_provider.dart';

class NewsfeedPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final NewsfeedBloc bloc = BlocProvider.of<NewsfeedBloc>(context);
    // here you should use a stream builder or such to build the ui
    return Container(
      child: Card(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            const ListTile(
              leading: Icon(Icons.album),
              title: Text('The Enchanted Nightingale'),
              subtitle: Text('Music by Julie Gable. Lyrics by Sidney Stein.'),
            ),
            ButtonTheme.bar(
              // make buttons use the appropriate styles for cards
              child: ButtonBar(
                children: <Widget>[
                  FlatButton(
                    child: const Text('BUY TICKETS'),
                    onPressed: () {/* do something with the bloc */},
                  ),
                  FlatButton(
                    child: const Text('LISTEN'),
                    onPressed: () {/* do something with the bloc */},
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

最后是包含导航底部栏和抽屉的 main.dart 文件:

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

import 'blocs/bloc_provider.dart';
import 'blocs/application_bloc.dart';
import 'blocs/newsfeed_bloc.dart';
import 'blocs/tracking_bloc.dart';
import 'blocs/notifications_bloc.dart';
import 'blocs/item1_bloc.dart';
import 'blocs/item2_bloc.dart';

import 'pages/newsfeed.dart';
import 'pages/tracking.dart';
import 'pages/notifications.dart';
import 'pages/item1.dart';
import 'pages/item2.dart';

Future<void> main() async {
  return runApp(BlocProvider<ApplicationBloc>(
    bloc: ApplicationBloc(),
    child: MyApp(),
  ));
}

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

class _MyAppState extends State<MyApp> {
  // define your blocs here so that you dont lose the state when your app rebuilds for some reason. thanks boformer for pointing that out.
  NewsfeedBloc _newsfeedBloc;

  PageController _pageController;
  var _page = 0;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Movies',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new Scaffold(
        appBar: AppBar(
          title: new Text('App Title'),
        ),
        body: PageView(
          children: <Widget>[
            BlocProvider<NewsfeedBloc>(
              bloc: _newsfeedBloc(),
              child: NewsfeedPage(),
            ),
            // ...
          ],
          controller: _pageController,
          onPageChanged: onPageChanged,
        ),
        bottomNavigationBar: BottomNavigationBar(
          items: [
            BottomNavigationBarItem(
              icon: Icon(Icons.timeline),
              title: Text("Timeline"),
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.art_track),
              title: Text("Some Page"),
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.notifications),
              title: Text("Notifications"),
            ),
          ],
          onTap: navigationTapped,
          currentIndex: _page,
        ),
        drawer: Drawer(
          child: ListView(
            padding: EdgeInsets.zero,
            children: <Widget>[
              DrawerHeader(
                child: Text('Settings'),
                decoration: BoxDecoration(
                  color: Colors.blue,
                ),
              ),
              ListTile(
                title: Text('Item 1'),
                onTap: () {
                    Navigator.of(context).push(MaterialPageRoute(builder: (BuildContext context) { 
                        return BlocProvider<Item1Bloc>(
                            bloc: Item1Bloc(),
                            child: Item1Page(),
                        );
                    }
                },
              ),
              ListTile(
                title: Text('Item 2'),
                onTap: () {
                    Navigator.of(context).push(MaterialPageRoute(builder: (BuildContext context) { 
                        return BlocProvider<Item2Bloc>(
                            bloc: Item2Bloc(),
                            child: Item2Page(),
                        );
                    }
                },
              ),
            ],
          ),
        ),
      ),
    );
  }

  void navigationTapped(int page) {
    _pageController.animateToPage(
      page,
      duration: Duration(milliseconds: 300),
      curve: Curves.easeIn,
    );
  }

  void onPageChanged(int page) {
    setState(() {
      this._page = page;
    });
  }

  @override
  void initState() {
    super.initState();
    _pageController = new PageController();
    _newsfeedBloc = NewsfeedBloc();    
  }

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

关于flutter - 具有 BLoC 模式的 BottomNavigationBar，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53012983/