android - Flutter 无法从 Assets 中加载文本

Question

我已阅读 https://flutter.dev/docs/development/ui/assets-and-images#asset-images-in-package-dependencies和 Flutter - Read text file from assets并应用了所有的东西，但我的代码仍然不起作用....
我为此打开了一个新项目，在主文件夹中我创建了 Assets 和一个文件:

pwd
 /home/bboett/AndroidStudioProjects/examen_companion
bboett@hayate:~/AndroidStudioProjects/examen_companion$ ls -l assets/
 insgesamt 4
 -rw-r--r-- 1 bboett bboett 10 19. Mai 15:14 test.txt
 bboett@hayate:~/AndroidStudioProjects/examen_companion$ cat assets/test.txt 
  Hello!!

然后，不信任 android studio，我检查了 vi，在 pubspec.yaml 中一切正常:
该文件以:

flutter:
 uses-material-design: true
 assets:
  - assets/

我替换了空间，在使用和 Assets 之前有 2 个空格:和 4 之前 - Assets ...
在 _MyHomePageState 类中我改变了:

  @override
  Widget build(BuildContext context)
  {
    AssetBundle bundle = DefaultAssetBundle.of(context);
    return FutureBuilder<String>(
        future: bundle.loadString("assets/test.txt"),
        builder: (context, AsyncSnapshot<String> snapshot)
        {
          if (snapshot.hasData) { return Text(snapshot.data.toString()); }
          else { return CircularProgressIndicator(); }
        }
  );
  }

不起作用....我从不退出进度指示器....
所以直接在我主要添加:

void main() async {
 print(await rootBundle.loadString("assets/test.txt"));
 runApp(MyApp());
}

并且崩溃与:

 Launching lib/main.dart on Linux in debug mode...
 Building Linux application...
 Debug service listening on ws://127.0.0.1:41355/L-ev6_eNIlI=/ws
 Syncing files to device Linux...
 [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: Null check operator used    on a null value
 #0      PlatformAssetBundle.load (package:flutter/src/services/asset_bundle.dart:222:39)
 #1      AssetBundle.loadString (package:flutter/src/services/asset_bundle.dart:68:33)
 #2      CachingAssetBundle.loadString.<anonymous closure> (package:flutter/src/services/asset_bundle.dart:165:56)
 #3      _LinkedHashMapMixin.putIfAbsent (dart:collection-patch/compact_hash.dart:311:23)
 #4      CachingAssetBundle.loadString (package:flutter/src/services/asset_bundle.dart:165:27)
 #5      main (package:examen_companion/main.dart:9:26)

我在运行之前改变了任何东西之后做了一个 flutter 的清洁......
版本是:

 flutter upgrade
  Flutter is already up to date on channel beta
  Flutter 2.2.0-10.3.pre • channel beta • https://github.com/flutter/flutter.git
  Framework • revision 06e2fd6357 (vor 11 Tagen) • 2021-05-08 11:28:22 -0700
  Engine • revision a123e75c60
  Tools • Dart 2.13.0 (build 2.13.0-211.14.beta)

flutter 医生也运行正常，哦，我在 linux 或 android 上也有同样的错误，所以它不是设备....
所以我对如何完成这项工作一无所知，因为我的印象是遵循了文档和以前的帮助:(
顺便说一句，我认为 flutter 现在是空的，安全的......无论如何，我该如何让它工作？
提前致谢
[编辑]:甚至更陌生....我替换了

    //future: bundle.loadString("assets/test.txt"),
    future: bundle.loadString('AssetManifest.json'),

并得到:

 flutter: {"assets/test.txt":["assets/test.txt"],"packages/cupertino_icons/assets/CupertinoIcons.ttf":["packages/cupertino_icons/assets/CupertinoIcons.ttf"]}

所以文件在那里？？？为什么我不能打开/得到它？
[ed2]:好的，我不明白......我直接在 main 中尝试了这个:

 print(await rootBundle.loadString('AssetManifest.json'));

并且也因空异常而崩溃....

Answer 1

WidgetsFlutterBinding.ensureInitialized()是解决我的问题以及@HannesHultergård 所写的关键。为了补充他的答案，主要应该是:

void main() async {
 WidgetsFlutterBinding.ensureInitialized();
 print(await rootBundle.loadString("assets/test.txt"));
 runApp(MyApp());
}