Flutter initState() 返回 _debugLifecycleState 错误

Question

我一直在构建 flutter 应用程序有一段时间了，一切似乎都运行良好，但今天我尝试调用initState()statefulWidget 以便我可以进行 API 调用，但它返回一个我不熟悉的错误

我的代码：

class Home extends StatefulWidget {

  final String header;

  Home({Key key, this.header}): super(key: key);

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

class _HomeState extends State<Home>{
  @override
  Widget build(BuildContext context) {

    Top top;
    bool _loading = true;

    fetchData() async {
      setState(() {
        _loading = true;
      });
      //Fetch top Animes
      var res = await http.get(Constants.topAnimes);
      var decodedJson = jsonDecode(res.body);
      print(decodedJson['top']);
      top = Top.fromJson(decodedJson['top']);
      print(top.toJson());


      setState(() {
        _loading = false;
      });
    }

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

    return Container();
  }
}

错误：

I/flutter (24395): ??? EXCEPTION CAUGHT BY WIDGETS LIBRARY ????????????????????????????????????????????????????????????
I/View    (24395): Key down dispatch to io.flutter.view.FlutterView{8dd5ba8 VFE...... .F...... 0,0-720,1200}, event = KeyEvent { action=ACTION_DOWN, keyCode=KEYCODE_F11, scanCode=87, metaState=0, flags=0x8, repeatCount=11805, eventTime=9200503, downTime=8597691, deviceId=2, source=0x101 }
I/flutter (24395): The following assertion was thrown building Home(dirty, state: _HomeState#5567f):
I/flutter (24395): 'package:flutter/src/widgets/framework.dart': Failed assertion: line 1008 pos 12:
I/flutter (24395): '_debugLifecycleState == _StateLifecycle.created': is not true.
I/View    (24395): Key down dispatch to io.flutter.view.FlutterView{8dd5ba8 VFE...... .F...... 0,0-720,1200}, event = KeyEvent { action=ACTION_DOWN, keyCode=KEYCODE_F11, scanCode=87, metaState=0, flags=0x8, repeatCount=11806, eventTime=9200553, downTime=8597691, deviceId=2, source=0x101 }
I/flutter (24395): 
I/flutter (24395): Either the assertion indicates an error in the framework itself, or we should provide substantially
I/flutter (24395): more information in this error message to help you determine and fix the underlying cause.
I/flutter (24395): In either case, please report this assertion by filing a bug on GitHub:
I/flutter (24395):   https://github.com/flutter/flutter/issues/new?template=BUG.md
I/flutter (24395): 
I/flutter (24395): When the exception was thrown, this was the stack:
I/flutter (24395): #2      State.initState (package:flutter/src/widgets/framework.dart:1008:12)
I/flutter (24395): #3      _HomeState.build.initState (package:flutter_anime/screens/home.dart:66:13)
I/flutter (24395): #4      _HomeState.build (package:flutter_anime/screens/home.dart:70:14)
I/flutter (24395): #5      StatefulElement.build (package:flutter/src/widgets/framework.dart:3825:27)
I/flutter (24395): #6      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3736:15)
I/flutter (24395): #7      Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #8      ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #9      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3864:11)
I/flutter (24395): #10     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #11     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #12     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #13     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/flutter (24395): #14     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #15     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #16     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #17     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #18     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #19     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #20     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #21     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #22     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/flutter (24395): #23     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #24     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #25     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/flutter (24395): #26     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #27     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #28     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/flutter (24395): #29     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #30     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #31     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/flutter (24395): #32     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #33     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #34     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #35     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #36     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #37     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3864:11)
I/flutter (24395): #38     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #39     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #40     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #41     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #42     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #43     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #44     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #45     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #46     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #47     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #48     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #49     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #50     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3864:11)
I/flutter (24395): #51     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #52     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #53     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #54     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/flutter (24395): #55     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #56     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #57     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #58     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #59     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #60     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #61     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #62     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #63     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/View    (24395): Key down dispatch to io.flutter.view.FlutterView{8dd5ba8 VFE...... .F...... 0,0-720,1200}, event = KeyEvent { action=ACTION_DOWN, keyCode=KEYCODE_F11, scanCode=87, metaState=0, flags=0x8, repeatCount=11809, eventTime=9200704, downTime=8597691, deviceId=2, source=0x101 }
I/flutter (24395): #64     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #65     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #66     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #67     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #68     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #69     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3864:11)
I/flutter (24395): #70     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #71     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #72     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #73     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #74     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #75     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #76     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #77     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #78     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #79     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/flutter (24395): #80     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #81     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #82     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #83     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #84     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #85     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #86     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #87     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #88     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #89     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #90     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #91     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3864:11)
I/flutter (24395): #92     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #93     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #94     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #95     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #96     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #97     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #98     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3864:11)
I/flutter (24395): #99     ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #100    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #101    MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4982:32)
I/flutter (24395): #102    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #103    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #104    _TheatreElement.mount (package:flutter/src/widgets/overlay.dart:494:16)
I/flutter (24395): #105    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #106    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #107    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #108    Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #109    ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #110    StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3864:11)
I/flutter (24395): #111    ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #112    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #113    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #114    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #115    Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #116    ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #117    ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #118    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #119    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #120    SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/flutter (24395): #121    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #122    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #123    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #124    Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #125    ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #126    StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3864:11)
I/flutter (24395): #127    ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #128    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #129    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #130    SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/flutter (24395): #131    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #132    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #133    SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4876:14)
I/flutter (24395): #134    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #135    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #136    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #137    Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #138    ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #139    StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3864:11) 
I/flutter (24395): #140    ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #141    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #142    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #143    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #144    Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #145    ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #146    ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #147    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #148    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #149    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #150    Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #151    ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #152    ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #153    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #154    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #155    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #156    Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #157    ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #158    ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #159    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #160    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #161    ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter (24395): #162    Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter (24395): #163    ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter (24395): #164    ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter (24395): #165    Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter (24395): #166    Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter (24395): #167    ComponentElement.performRebuild (package:flutte

    

Answer 1

您的所有状态属性和 initState 方法都在您的构建方法中。将它们移到 build 方法之外。此外，变量的初始值为_loading真，因此无需在fetchData函数开始时再次将其设置为真。

class Home extends StatefulWidget {
  final String header;

  Home({Key key, this.header}): super(key: key);

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

class _HomeState extends State<Home>{
  Top top;
  bool _loading = true;

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

  @override
  Widget build(BuildContext context) {
    if(_loading) {
        return CircularProgressIndicator();
    }

    return Container(
        child: Text("LOADED");
    );
  }

  fetchData() async {
    //Not needed since it's already set to true.
    /*setState(() {
      _loading = true;
    });*/

    //Fetch top Animes
    var res = await http.get(Constants.topAnimes);

    var decodedJson = jsonDecode(res.body);
    print(decodedJson['top']);

    top = Top.fromJson(decodedJson['top']);
    print(top.toJson());

    setState(() {
      _loading = false;
    });
  }
}