List< String>为空，但值在重新加载后返回

问题描述：

我正在尝试从.txt文件中逐行加载不同的值.

I'm trying to load different values from a .txt file line by line.

我正在从资产中加载文件，该文件已在pubspec.yaml中注册.

I'm loading an file from assets, which is already registered in pubspec.yaml.

Future<String> getFileData() async {
  return await rootBundle.loadString('assets/files/text.txt');
}

当这返回一个长字符串时，我将其拆分为一个列表:

As this returns one long String I split it into a list:

void doStuff() async {
  await getFileData().then((value) => value.split('\n').forEach((element) {
        exampleQuestions.add(element);
      }));
}

在我的类中调用此方法-构造函数，该构造函数是从Main中通过命名路由调用的:

This method is called in my class - constructor which is called from my Main by a named route:

  GameOver.routeName: (context) => GameOver(),
    '/game': (context) => Game(

        ),
  },

exampleQuestion获得的内容已填充到doStuff()方法中(已进行了检查)，但在_GameState类中失去了它的值，该类要访问该列表的小部件将返回索引不足的异常.

exampleQuestion get's filled in the doStuff() - method (already checked that), but looses it's values in the _GameState class where the widget, that want's to access the list returns an out of index exception.

但是，如果我快速重新加载应用程序，则值设置正确.如果我再单击该按钮以再次继续，则直到我快速重新加载为止，一切都没有改变.

However if i quick reload my application the values are set correctly. If I then click the button to continue again nothing changes until I quick reload.

任何提示都非常感激..

Any hints are very appreciated ..

答

您不应在小部件构造函数中调用这种异步方法，因为在每次构建时都会调用它们.

You should not call asynchronous methods like this in widget constructors, because they'll be called on every build.

您应该使用带有 FutureBuilder 的 StatefulWidget .

另一方面，应该使用 LineSplitter 来分割行.

On another note, LineSplitter should be used for splitting lines.

class _MyWidgetState extends State<MyWidget> {
  late final Future<List<String>> _exampleQuestionsFuture;

  static Future<String> _getFileData() => rootBundle.loadString('assets/files/text.txt');

  @override
  void initState() {
    super.initState();
    _exampleQuestionsFuture = _getFileData().then(const LineSplitter().convert);
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<List<String>>(
      future: _exampleQuestionsFuture,
      builder: (snapshot, data) {
        /* ... */
      },
    );
  }
}

List< String>为空，但值在重新加载后返回

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