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我已经看到了很多关于这个主题的讨论，但还没有为我的问题找到合适的解决方案。

我想要实现的是Process.id从 ListView 传递到第二个小部件，然后在第二个小部件中 - 从 SQLite 加载对象并用Process数据更新 Scaffold 中的其他小部件。

我已经设法做到了（部分），因为我正在努力将数据加载到 ListView 小部件（我必须解析 json String 以创建 List，然后每当我尝试使用 List 更新 ListView.builder -我得到空白屏幕和异常）。注释掉 ListView.builder - 小部件工作正常......可能我将代码放在错误的位置......

这就是我的代码的样子：

  1. 从Widget 1Process.id中的 ListView传递... 

    ...
return new ListTile(
     onTap: () {
     Navigator.push(
        context, 
        MaterialPageRoute(builder: (context) => ScreenProcessDetails(processId: _newProcesses[index].id)));}, 
...

    到小部件 2 ->完成：

    class ScreenProcessDetails extends StatefulWidget {
    final int processId;

    ScreenProcessDetails({Key key, @required this.processId}) : super(key: key);

    @override
        State createState() {
        return new _ScreenProcessDetailsState();
    }
}

  2. 在Widget 的 2 -> DONE 中从 SQLite加载Process对象（使用 SQFlite），如下所示： ScreenProcessDetails initState()

    class _ScreenProcessDetailsState extends State<ScreenProcessDetails> {
    Process process;

    Future<Process> getProcess(int id) async {
        process = await _repository.getProcess(id);
        setState(() {
        });
    }

    @override
    void initState() {
      super.initState();
      getProcess(widget.processId);
    }

    @override
    Widget build(BuildContext context) {
    String defaultValue = process.defaultValue;
    List<dynamic> filesJson = jsonDecode(process.files);
    filesList = filesJson.map((i) => new Files.fromJson(i)).toList();

        return new Scaffold(
          appBar: new AppBar(title: new Text(process.name)),
          body: Builder (builder: (context) => new Container(
                child: new Column(
                  children: <Widget>[
                    new Text(process.name),
                    new TextFormField(initialValue: defaultValue,),
                    new ListView.builder(
                      physics: const NeverScrollableScrollPhysics(),
                      itemCount: filesList.length,
                      itemBuilder: (context, int index) {
                        return new ListTile(
                          leading: new Icon(Icons.archive, color: Colors.amber),
                          title: new Text(filesList[index].name),
                          subtitle: new Text(filesList[index].guid),
                          );
                      })
    //skipped rest of code 
}

但是filesList 没有加载- 整个屏幕都是白色的，我正在获取异常列表（如下）。我想知道我可能做错了什么？我已经尝试过使用String我的对象的 instedProcess没有运气。

还有一件事 - 我的意思是从 SQLiteinitState()正确加载对象吗？因为我看到一个例外：

2019-02-20 13:02:13.023 19208-19288/pl.itelix.documentapp I/flutter: Another exception was thrown: NoSuchMethodError: The getter 'name' was called on null.

这（据我了解）意味着该对象为空......但整个小部件是正确构建的？！

或者我应该使用加载 SQLite 数据Future然后开始加载整个小部件树？还有一件事——我尝试使用 FutureBuilder，但每次我尝试在 TextField 中输入文本时都会重新创建它。

例外：

2019-02-20 12:41:07.490 19208-19288/documentapp I/flutter: Another exception was thrown: Vertical viewport was given unbounded height.
2019-02-20 12:41:07.492 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderViewport#627ff NEEDS-LAYOUT NEEDS-PAINT
2019-02-20 12:41:07.493 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderViewport#627ff NEEDS-PAINT
2019-02-20 12:41:07.496 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderIgnorePointer#e5843 relayoutBoundary=up26 NEEDS-PAINT
2019-02-20 12:41:07.500 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderSemanticsAnnotations#bb781 relayoutBoundary=up25 NEEDS-PAINT
2019-02-20 12:41:07.502 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderPointerListener#57754 relayoutBoundary=up24 NEEDS-PAINT
2019-02-20 12:41:07.503 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderSemanticsGestureHandler#54f57 relayoutBoundary=up23 NEEDS-PAINT
2019-02-20 12:41:07.505 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: _RenderScrollSemantics#1370c relayoutBoundary=up22 NEEDS-PAINT
2019-02-20 12:41:07.507 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#c4b4e relayoutBoundary=up21 NEEDS-PAINT
2019-02-20 12:41:07.508 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderCustomPaint#88d67 relayoutBoundary=up20 NEEDS-PAINT
2019-02-20 12:41:07.510 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#b4040 relayoutBoundary=up19 NEEDS-PAINT
2019-02-20 12:41:07.511 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderFlex#09183 relayoutBoundary=up18 NEEDS-PAINT
2019-02-20 12:41:07.513 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderPadding#50678 relayoutBoundary=up17 NEEDS-PAINT
2019-02-20 12:41:07.515 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: _RenderInkFeatures#de7b5 relayoutBoundary=up16 NEEDS-PAINT
2019-02-20 12:41:07.517 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderCustomPaint#05457 relayoutBoundary=up15 NEEDS-PAINT
2019-02-20 12:41:07.519 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderPhysicalShape#2b262 relayoutBoundary=up14 NEEDS-PAINT
2019-02-20 12:41:07.520 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderPadding#5eb3c relayoutBoundary=up13 NEEDS-PAINT
2019-02-20 12:41:07.522 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderSemanticsAnnotations#e3fcc relayoutBoundary=up12 NEEDS-PAINT
2019-02-20 12:41:07.524 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderFlex#8eaef relayoutBoundary=up11 NEEDS-PAINT
2019-02-20 12:41:07.525 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: _RenderSingleChildViewport#c3635 relayoutBoundary=up10 NEEDS-PAINT
2019-02-20 12:41:07.526 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderIgnorePointer#c220a relayoutBoundary=up9 NEEDS-PAINT
2019-02-20 12:41:07.529 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderSemanticsAnnotations#bf875 relayoutBoundary=up8 NEEDS-PAINT
2019-02-20 12:41:07.530 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderPointerListener#789f6 relayoutBoundary=up7 NEEDS-PAINT
2019-02-20 12:41:07.532 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderSemanticsGestureHandler#cabf4 relayoutBoundary=up6 NEEDS-PAINT
2019-02-20 12:41:07.533 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: _RenderScrollSemantics#8ab03 relayoutBoundary=up5 NEEDS-PAINT
2019-02-20 12:41:07.535 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#274a1 relayoutBoundary=up4 NEEDS-PAINT
2019-02-20 12:41:07.536 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderCustomPaint#6174f relayoutBoundary=up3 NEEDS-PAINT
2019-02-20 12:41:07.538 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#a452d relayoutBoundary=up2 NEEDS-PAINT
2019-02-20 12:41:07.539 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderPadding#8c834 relayoutBoundary=up1 NEEDS-PAINT
2019-02-20 12:41:07.543 19208-19288/documentapp I/flutter: Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#a452d relayoutBoundary=up2 NEEDS-PAINT

非常感谢任何帮助！先感谢您！:)

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1 回答 1

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发现问题 - 列中的 ListView 必须包含在 Flex/Extended 小部件中。

于 2019-02-22T08:58:33.203 回答