flutter - [Flutter][BLoC] 返回上一个小部件时出错

Question

最近我一直在尝试更新个人资料。所以这里是场景， HomePage => Drawer => Profile => HomePage 。当我返回时，这是我得到的错误。

⡿flutter: ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
flutter: The following assertion was thrown building BlocListener<HomeBloc, HomeState>(dirty, state:
flutter: _BlocListenerBaseState<HomeBloc, HomeState>#4a7df):
flutter: A build function returned null.
flutter: The offending widget is:
flutter:   BlocListener<HomeBloc, HomeState>
flutter: Build functions must never return null.
flutter: To return an empty space that causes the building widget to fill available room, return
flutter: "Container()". To return an empty space that takes as little room as possible, return
flutter: "Container(width: 0.0, height: 0.0)".
flutter:
flutter: The relevant error-causing widget was:
flutter:   BlocListener<HomeBloc, HomeState>
flutter:   file:///Users/macbook/Documents/development/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_bloc-6.0.6/lib/src/bloc_builder.dart:148:12
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #0      debugWidgetBuilderValue.<anonymous closure> (package:flutter/src/widgets/debug.dart:302:7)
flutter: #1      debugWidgetBuilderValue (package:flutter/src/widgets/debug.dart:323:4)
flutter: #2      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4632:7)
flutter: #3      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #4      Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #5      StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #6      Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #7      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #8      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #9      Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #10     StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #11     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #12     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #13     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #14     StatelessElement.update (package:flutter/src/widgets/framework.dart:4708:5)
flutter: #15     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #16     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #17     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #18     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #19     StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #20     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #21     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #22     _InheritedProviderScopeElement.performRebuild (package:provider/src/inherited_provider.dart:426:11)
flutter: #23     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #24     ProxyElement.update (package:flutter/src/widgets/framework.dart:4987:5)
flutter: #25     _InheritedProviderScopeElement.update (package:provider/src/inherited_provider.dart:446:11)
flutter: #26     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #27     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #28     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #29     StatelessElement.update (package:flutter/src/widgets/framework.dart:4708:5)
flutter: #30     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #31     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #32     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #33     StatelessElement.update (package:flutter/src/widgets/framework.dart:4708:5)
flutter: #34     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #35     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
flutter: #36     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #37     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #38     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #39     StatelessElement.update (package:flutter/src/widgets/framework.dart:4708:5)
flutter: #40     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #41     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
flutter: #42     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #43     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
flutter: #44     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #45     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #46     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #47     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #48     StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #49     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #50     RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:5647:32)
flutter: #51     MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6246:17)
flutter: #52     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #53     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #54     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #55     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #56     StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #57     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #58     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
flutter: #59     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #60     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #61     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #62     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #63     StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #64     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #65     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
flutter: #66     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #67     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #68     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #69     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #70     StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #71     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #72     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
flutter: #73     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #74     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #75     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #76     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #77     StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #78     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #79     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #80     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #81     StatelessElement.update (package:flutter/src/widgets/framework.dart:4708:5)
flutter: #82     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #83     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #84     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #85     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #86     StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #87     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #88     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
flutter: #89     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #90     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #91     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #92     ProxyElement.update (package:flutter/src/widgets/framework.dart:4987:5)
flutter: #93     _InheritedNotifierElement.update (package:flutter/src/widgets/inherited_notifier.dart:183:11)
flutter: #94     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #95     SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
flutter: #96     Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #97     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #98     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #99     Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #100    StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #101    Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #102    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #103    Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #104    ProxyElement.update (package:flutter/src/widgets/framework.dart:4987:5)
flutter: #105    Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #106    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #107    StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #108    Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #109    StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
flutter: #110    Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #111    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #112    Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #113    StatelessElement.update (package:flutter/src/widgets/framework.dart:4708:5)
flutter: #114    Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #115    SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
flutter: #116    Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #117    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #118    Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #119    ProxyElement.update (package:flutter/src/widgets/framework.dart:4987:5)
flutter: #120    Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
flutter: #121    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
flutter: #122    StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
flutter: #123    Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
flutter: #124    BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2730:33)
flutter: #125    WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:913:20)
flutter: #126    RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:302:5)
flutter: #127    SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1117:15)
flutter: #128    SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1055:9)
flutter: #129    SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:864:7)
flutter: (elided 4 frames from class _RawReceivePortImpl, class _Timer, and dart:async-patch)
flutter:
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════

这是我的 BlocConsumer 代码：

BlocConsumer<PrivateprofileBloc, PrivateprofileState>(
              builder: (context, state) {
                if (state is PrivateprofileInitial) {
                  return bodyBuild();
                } else if (state is PrivateprofilePictureUpdate) {
                  this.user = state.user;
                  return bodyBuild();
                } else if (state is PrivateprofileUpdate) {
                  this.user = state.user;
                  return bodyBuild();
                } else if (state is PrivateprofileReturn) {
                  return BlocProvider(
                      create: (context) => HomeBloc(state.user),
                      child: HomePage(state.user));
                }
              },
              listener: (context, state) {},
            )

知道为什么吗？数据得到更新，我用更新的数据再次返回主页，但我在终端中收到该错误。

标签： flutterbloc

Answer 1

因为您没有在 BlocBuilder 的“其他”情况下返回 Widget。
只需在“BlocBuilder”中返回空容器。
我知道'listener'返回'void'，你不需要返回任何东西。

BlocConsumer<HomeBloc, HomeState>(
    builder: (context, state) { 
        if (state is HomeInitial) { 
            return buildBody(); 
        } else if (state is HomeUpdatedUser) { 
            widget._user = state.user; 
            return buildBody(); 
        } 
        return Container();
    }, 
    
);