Question

在我的应用中，我正在将数据导出到JSON。但是，当我尝试导入JSON文件时，它将引发类似于以下内容的错误：

E / flutter：[错误：flutter / shell / common / shell.cc（184）] Dart错误：未处理的异常： NoSuchMethodError：方法'[]'在null上调用。接收者：null 尝试致电：＃0 Object.noSuchMethod（dart：core / runtime / libobject_patch.dart：50：5）＃1 _ $ RecipesModelFromJson（文件：///home/stube/IdeaProjects/Flutter_Recipe/lib/JSON/recipes.g.dart：11：11）＃2 new RecipesModel.fromJson（package：Time2Eat / JSON / recipes.dart：20：63）＃3 _ $ RecipesModelFromJson（文件：///home/stube/IdeaProjects/Flutter_Recipe/lib/JSON/recipes.g.dart：32：22）＃4 new RecipesModel.fromJson（package：Time2Eat / JSON / recipes.dart：20：63）＃5 RecipebookState.createRecipeJson（package：Time2Eat / recipe / recipebook.dart：111：32）＃6 RecipebookState.getPath（package：Time2Eat / recipe / recipebook.dart：123：9）＃7 RecipebookState.build。（包：Time2Eat / recipe / recipebook.dart：185：19）＃8 AnimatedChild._performAction（package：flutter_speed_dial / src / animated_child.dart：60：24）＃9 _InkResponseState._handleTap（包：flutter / src / material / ink_well.dart：507：14）＃10 _InkResponseState.build。（包：flutter / src / material / ink_well.dart：562：30）＃11 GestureRecognizer.invokeCallback（package：flutter / src / gestures / recognizer.dart：102：24）＃12 TapGestureRecognizer._checkUp（包：flutter / src / gestures / tap.dart：242：9）＃13 TapGestureRecognizer.handlePrimaryPointer（软件包：flutter / src / gestures / tap.dart：175：7）＃14 PrimaryPointerGestureRecognizer.handleEvent（package：flutter / src / gestures / recognizer.dart：315：9）＃15 PointerRouter._dispatch（软件包：flutter / src / gestures / pointer_router.dart：73：12）＃16 PointerRouter.route（软件包：flutter / src / gestures / pointer_router.dart：101：11）＃17 _WidgetsFlutterBinding＆BindingBase＆GestureBinding.handleEvent（package：flutter / src / gestures / binding.dart：180：19）＃18 _WidgetsFlutterBinding＆BindingBase＆GestureBinding.dispatchEvent（package：flutter / src / gestures / binding.dart：158：22）＃19 _WidgetsFlutterBinding＆BindingBase＆GestureBinding._handlePointerEvent（package：flutter / src / gestures / binding.dart：138：7）＃20 _WidgetsFlutterBinding＆BindingBase＆GestureBinding._flushPointerEventQueue（package：flutter / src / gestures / binding.dart：101：7）＃21 _WidgetsFlutterBinding＆BindingBase＆GestureBinding._handlePointerDataPacket（包：flutter / src / gestures / binding.dart：85：7）＃22 _invoke1（dart：ui / hooks.dart：173：13）＃23 _dispatchPointerDataPacket（dart：ui / hooks.dart：127：5）

由json_serializable生成的

recipes.g.dart ：

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

RecipesModel _$RecipesModelFromJson(Map<String, dynamic> json) {
  return RecipesModel(
      json['name'] as String,
      json['image'] as String,
      json['description'] as String,
      json['favorite'] as int,
      json['timestamp'] as String,
      json['preperation'] as String,
      json['creation'] as String,
      json['resting'] as String,
      json['people'] as String,
      json['backgroundColor'] as String,
      (json['zutaten'] as List)
          ?.map((e) => e == null
              ? null
              : ZutatenModel.fromJson(e as Map<String, dynamic>))
          ?.toList(),
      (json['zubereitung'] as List)
          ?.map((e) => e == null
              ? null
              : ZubereitungModel.fromJson(e as Map<String, dynamic>))
          ?.toList())
    ..recipeModel =
        RecipesModel.fromJson(json['recipeModel'] as Map<String, dynamic>);
}

Map<String, dynamic> _$RecipesModelToJson(RecipesModel instance) =>
    <String, dynamic>{
      'name': instance.name,
      'image': instance.image,
      'description': instance.description,
      'favorite': instance.favorite,
      'timestamp': instance.timestamp,
      'preperation': instance.preperation,
      'creation': instance.creation,
      'resting': instance.resting,
      'people': instance.people,
      'backgroundColor': instance.backgroundColor,
      'zutaten': instance.zutaten,
      'zubereitung': instance.zubereitung,
      'recipeModel': instance.recipeModel
    };

ZutatenModel _$ZutatenModelFromJson(Map<String, dynamic> json) {
  return ZutatenModel(
      json['zutat'] as String,
      json['number'] as String,
      json['measure'] as String
  );
}

Map<String, dynamic> _$ZutatenModelToJson(ZutatenModel instance) =>
    <String, dynamic>{
      'zutat': instance.zutat,
      'number': instance.number,
      'measure': instance.measure
    };

ZubereitungModel _$ZubereitungModelFromJson(Map<String, dynamic> json) {
  return ZubereitungModel(json['number'] as String, json['steps'] as String);
}

Map<String, dynamic> _$ZubereitungModelToJson(ZubereitungModel instance) =>
    <String, dynamic>{'number': instance.number, 'steps': instance.steps};

我正在函数内部调用RecipesModel.fromJson（）方法，该函数应该能够将此数据保存在数据库中。该函数如下所示：

createJson() async{
      FlutterDocumentPickerParams params = FlutterDocumentPickerParams(
          allowedFileExtensions: ['json'],
          invalidFileNameSymbols: ['/']
      );
      final path = await FlutterDocumentPicker.openDocument(params: params);
      File file = new File(path);
      createRecipeJson(file);
      Map<String,dynamic> jSON = json.decode(path.readAsStringSync());
      var model = RecipesModel.fromJson(jSON);
      showBottomSnack("Name: ${model.name}", ToastGravity.BOTTOM);
    }

我希望有人能帮助我并解决我的问题。太棒了。

Answer 1

检查类成员中的@JsonSerializable(nullable: false)（从ZutatenModel和RecipeModel开始）。

如果您期望它们有时为null，则在注释其模型类时不要标记nullable: false。

在这种情况下，请将其更改为@JsonSerializable(nullable: true)。顺便说一句，默认设置为true。

当提供某些类属性null时，通常会发生此异常，但是(nullable: false)向JsonSerializer建议这些属性不会为空。

Flutter-来自Json的json_serializable：方法'[]'在null

1 个答案: