Question

我试图用来自宁静的api的数据填充flutter应用程序中的下拉按钮。但是我得到上面的错误。

这是我的模特；

class SavingsCategory extends Equatable{
    final int id;
    final String name;

   SavingsCategory({
     @required this.id, 
     @required this.name
   });

 @override
 List<Object> get props => [name, id];

}

我的存储库正在获取数据

  @override
  Future<List<SavingsCategory>> getSavingsCategory() 
 async {
var token = await tokenRepository.getToken();

final response = await http.get(
  '$baseUrl/user/savings-category',
  headers: {HttpHeaders.authorizationHeader: 'Bearer $token'},
  );

  if (response.statusCode == 200) {
     var data = json.decode(response.body);

    List<SavingsCategory> categoryList = data['savingsCategory'].map<SavingsCategory>((json) {
        return SavingsCategory.fromJson(json);
    }).toList();
    return categoryList;
  } else {
    throw new Exception("Couldn't get any saving categories");
  }

}

我的集团代码

class SavingsCategoryBloc {
    final repository = SavingsRepository();
    final _savingsCategories = PublishSubject<List<SavingsCategory>>();

    Stream<List<SavingsCategory>> get savingsCategories => _savingsCategories.stream;

   fetchSavingsCategories() async {
  final categories = await repository.getSavingsCategory();
  _savingsCategories.sink.add(categories);
  }


  dispose(){
  _savingsCategories.close();
}

}

最后是我的小部件

class _StartSavingPageState extends State<StartSavingPage> {
    final SavingsCategoryBloc bloc = SavingsCategoryBloc();

    @override
    void initState() {
    bloc.fetchSavingsCategories();
    super.initState();
 }

 @override
 Widget build(BuildContext context) { 
 ....
     Container(
                      padding: EdgeInsets.symmetric(
                          horizontal: 15.0, vertical: 10.0),
                      child: StreamBuilder<List<SavingsCategory>>(

                          stream: bloc.savingsCategories,
                          builder: (context, snapshot) {
                            if (!snapshot.hasData) {
                              return DropdownButton<String>(

                                items: [
                                  DropdownMenuItem<String>(
                                    child: Text('No Savings Category'),
                                    value: '',
                                  ),
                                ],
                                onChanged: (String value) {
                                  setState(() {

                                  });
                                },
                                isExpanded: true,
                                hint: Text(
                                  'SAVING FOR?',
                                  style: TextStyle(
                                      fontSize: 15.0, color: Colors.grey),
                                ),
                              );
                            }
                            return DropdownButton(
                              value: category,
                              items: snapshot.data.map((category) {
                                DropdownMenuItem(
                                  child: Text('${category.name}'),
                                  value: category.id,
                                );
                              }).toList(),
                              onChanged: (value) {
                                setState(() {
                                  category = value;
                                });
                              },

                              isExpanded: true,
                              hint: Text(
                                'SAVING FOR?',
                                style: TextStyle(
                                    fontSize: 15.0, color: Colors.grey),
                              ),
                            );

                          }),
                    ),  
    }
}

如何解决此错误？我知道数据获取工作正常。我的窗口小部件肯定缺少某些内容。任何帮助将不胜感激。

Answer 1

DropdownButton值必须在项目值中，或者必须为null。

DropdownButton(
  value: categoryId,
  items: snapshot.data.map((category) {
    DropdownMenuItem(
      child: Text('${category.name}'),
      value: category.id,
    );
  }).toList(),
  onChanged: (value) {
    setState(() {
      categoryId = value;
    });
  },

  isExpanded: true,
  hint: Text(
    'SAVING FOR?',
    style: TextStyle(
        fontSize: 15.0, color: Colors.grey),
  ),
);

Flutter DropdownButton NoSuchMethodError：在null上调用了getter值

1 个答案: