Flutter bloc：更新状态不会重新调用 BlocBuilder

Question

我有一个使用 bloc 管理的页面

这里是home_state.dart

import 'package:banha/data/models/category.dart';
import 'package:flutter/material.dart';

abstract class HomeState {
  HomeState() : super();
}

class HomeInitial extends HomeState {}

class UpdateCats extends HomeState {
  final List<Category> cats;
  final int rand;
  UpdateCats({@required this.cats,@required this.rand}){
    print(this.cats);
    print(this.rand);
  }
}

还有home_bloc.dart（注意：随机数只是为了确保状态与前一个不同）

import 'dart:math';

import 'package:banha/data/models/category.dart';
import 'package:banha/data/network/categories.dart';
import 'package:banha/ui/tabs/home/bloc/home_events.dart';
import 'package:banha/ui/tabs/home/bloc/home_states.dart';
import 'package:bloc/bloc.dart';

class HomeBloc extends Bloc<HomeEvents, HomeState> {
  getAllCats() {
    dispatch(HomeGetCategories());
  }

  HomeBloc() : super();

  @override
  HomeState get initialState => HomeInitial();

  @override
  Stream<HomeState> mapEventToState(HomeEvents event) async* {
    if (event is HomeGetCategories) {
      yield* _getCats();
    }
  }

  Stream<HomeState> _getCats() async* {
    print("getting cats");
    List<Category> newCats;
    await Network_getAllCategories().then((List<Category> cats) {
      newCats = cats;
    });
    yield UpdateCats(cats: newCats, rand: Random().nextInt(21312545));
  }
}

和页面小部件：

import 'package:banha/ui/category/category.dart';
import 'package:banha/ui/tabs/home/bloc/home_bloc.dart';
import 'package:banha/ui/tabs/home/bloc/home_states.dart';
import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

class ListingsWidget extends StatefulWidget {
  @override
  _ListingsWidgetState createState() => _ListingsWidgetState();
}

class _ListingsWidgetState extends State<ListingsWidget> {
  final HomeBloc _homeBloc = HomeBloc();

  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 130,
      padding: EdgeInsets.only(top: 10, bottom: 10),
      child: BlocListener(
        bloc: _homeBloc,
        listener: (context, state) {
          print(state);
        },
        child: BlocBuilder<HomeBloc, HomeState>(
          bloc: _homeBloc,
          builder: (BuildContext context,HomeState state) {
            if(state is UpdateCats){
              print(state.cats);
            }
            return ListView(
              scrollDirection: Axis.horizontal,
              children: <Widget>[
                InkWell(
                  borderRadius: BorderRadius.circular(1000),
                  onTap: () {
                    HomeBloc().getAllCats();
//                    Navigator.push(context, CupertinoPageRoute(builder: (context) => CategoryPage()));
                  },
....

问题在于，在视图（小部件）中，BlocBuilder 仅在初始时被调用一次，但是当我尝试使用 HomeBloc().getAllCats(); 测试更改状态然后使用此代码打印新状态时：

if(state is UpdateCats){
              print(state.cats);
            }

什么都没有发生（不再调用 Builder），我的代码有什么问题？

Answer 1

问题出在这里：

...
onTap: () {
...
  HomeBloc().getAllCats();
...
},
...

应该是_homeBloc.getAllCats();

Answer 2

我将BlocProvider 添加到根小部件（即主页）并解决了问题。