"The declaration 'setState' isn't referenced." StatefulWidget 中的 DropdownButton 警告

Question

我有一个有状态的小部件，我在其中放置了 DropdownButton。在 DropdownButton 的 onChange 事件中，我有一个 setState 但它一直警告我未引用声明 'setState'。实际上，无论何时触发 onChange 事件，它都不会被调用。

如有任何建议，我们将不胜感激。

请参阅下面的代码片段以了解更多详细信息。

class TypeSetup extends StatefulWidget {
  const TypeSetup({Key? key}) : super(key: key);

  @override
  _TypeSetupState createState() => _TypeSetupState();
}

class _TypeSetupState extends State<TypeSetup> {
  var _selectedType;
  List<Type>? _types;

  @override
  void initState() {
    super.initState();

    loadTypeJson();
  }

  Future loadTypeJson() async {
    String typeJson = await DefaultAssetBundle.of(context)
        .loadString("assets/data/types.json");

    Iterable typeIter = json.decode(typeJson)["accommodation-types"];

    setState(() {
      _types = List<Type>.from(typeIter.map((model) => Type.fromJson(model)));
    });
  }

  @override
  Widget build(BuildContext context) {
    final typeList = _types?.map((model) {
      return new DropdownMenuItem<String>(
        value: model.type,`enter code here`
        child: new Text(model.name),
      );
    }).toList();

    return Container(
      padding: EdgeInsets.all(DefaultPalette.defaultPadding),
      decoration: BoxDecoration(
        color: DefaultPalette.secondaryColor,
        borderRadius: const BorderRadius.all(Radius.circular(10)),
      ),
      child: Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
        Text(
          "Set up",
          style: Theme.of(context).textTheme.subtitle1,
        ),
        SizedBox(
            width: double.infinity,
            child: Center(
                child: Padding(
                    padding: const EdgeInsets.all(16.0),
                    child: Container(
                      padding: EdgeInsets.only(left: 16, right: 16),
                      decoration: BoxDecoration(
                          border: Border.all(color: Colors.grey, width: 1),
                          borderRadius: BorderRadius.circular(13)),
                      child: DropdownButton(
                        hint: Text('Select  Type'),
                        dropdownColor: Colors.white,
                        icon: Icon(Icons.arrow_drop_down),
                        iconSize: 30,
                        isExpanded: true,
                        underline: SizedBox(),
                        style: TextStyle(color: Colors.black, fontSize: 22),
                        value: _selectedType,
                        onChanged: (newValue) {
                          setState() {
                            _selectedType = newValue;
                            print("Selected type changed.");
                          }
                        },
                        items: typeList,
                      ),
                    )
                )
            )
          )
      ]),
    );
  }
}

Answer 1

你需要这样调用setState

setState(() {
  _selectedType = newValue;
});

"The declaration 'setState' isn't referenced." StatefulWidget 中的 DropdownButton 警告

"The declaration 'setState' isn't referenced." warning for DropdownButton within StatefulWidget

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