断言行 5120 pos 12 失败：'child = _child' 不正确答案

【问题标题】：Failed assertion line 5120 pos 12: 'child = _child' is not true断言行 5120 pos 12 失败：'child = _child' 不正确
【发布时间】：2020-02-01 10:36:51
【问题描述】：

我正在尝试使用 bloc 模式创建一个包含 API 数据的列表视图，错误如下：

'package:flutter/src/widgets/framework.dart'：断言失败：第 5120 行 pos 12：'child == _child'：不正确。

我的列表文件：

import 'package:Instant_Feedback/Dashboard/PeopleList/bloc/bloc.dart';
import 'package:Instant_Feedback/People/strongConnection_model.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

class PeopleListing extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _PeopleListingState();
}
class _PeopleListingState extends State<PeopleListing> {
  PeopleListBloc peopleBloc;
  @override
  void initState() {
    super.initState();
    peopleBloc = BlocProvider.of<PeopleListBloc>(context);
    peopleBloc.dispatch(DisplayPeopleList());
  }

  @override
  Widget build(BuildContext context) {
    return BlocBuilder(
      bloc: peopleBloc,
      builder: (context, state){
        if (state is PeopleUninitializedState) {
          print("PeopleUninitializedState");
        } else if (state is PeopleFetchingState) {
          print("PeopleFetchingState");
        } else if (state is PeopleFetchingState) {
          print("PeopleFetchingState");
        } else {
          final stateAsPeopleFetchedState = state as PeopleFetchedState;
          final players = stateAsPeopleFetchedState.people;
          return buildPeopleList(players);
        }
      },
    );
  }

Widget buildPeopleList(List<StrongConnection_model> people) {
    print(people.length);
    return Container(
      child: Text('sdf sdkfh kdj'),
    );
  }
}

错误：

【问题讨论】：

你能尝试对人们做空检查吗？
除了else 情况外，您不会返回任何小部件。您必须在builder 中不断返回一个小部件。否则你会得到这个错误。只需在 if 条件循环之外返回 SizedBox。

标签： flutter bloc

【解决方案1】：

问题是，builder() 需要一个小部件，而您没有在 if/else if 条件下返回一个有效的小部件。尝试将您的代码更改为以下版本。

@override
Widget build(BuildContext context) {
    return BlocBuilder(
        bloc: peopleBloc,
        builder: (context, state){
            if (state is PeopleUninitializedState) {
                <!-- Expects A Widget -->
                print("PeopleUninitializedState");
                return SizedBox();
            } else if (state is PeopleFetchingState) {
                <!-- Expects A Widget -->
                print("PeopleFetchingState");
                return SizedBox();
            } else if (state is PeopleFetchingState) {
                <!-- Expects A Widget -->
                print("PeopleFetchingState");
                return SizedBox();
            } else {
                final stateAsPeopleFetchedState = state as PeopleFetchedState;
                final players = stateAsPeopleFetchedState.people;
                return buildPeopleList(players);
            }
        },
    );
}

【讨论】：

但是，我也被用在未来建造者的每个条件下。但是，它仍然给出与我使用链接 futurebuilder 相同的错误

【解决方案2】：

对于其他人，那些寻找此异常但答案与您的代码不匹配的人，我的提示是您应该跟踪您的子异常。当您的子班级出现问题时，通常会发生此异常。尝试撤消更改。请参阅子类 initState 的选项。

【讨论】：

【解决方案3】：

将脚手架添加到导致错误的小部件

【讨论】：

【解决方案4】：

简单的答案就是导入库**

导入 'package:flutter/src/widgets/framework.dart';

这对我有用，我希望它也对你有用。

【讨论】：