使用onPress检索数据

Question

当我试图使用文本小部件呈现item时，我收到了一个错误，说明它是未定义的。

当按下按钮时，如何检索值并将其放入小部件中？

class AddCashForm extends StatefulWidget {
  @override
  _AddCashFormState createState() => _AddCashFormState();
}

class _AddCashFormState extends State<AddCashForm> {
  DateTime selectedDate = DateTime.now();
  List<String> chipList = [
    "one",
    "two",
    "three",
    "four",
  ];

  void dispose() {
    oneController.dispose();
    twoController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Row(
            children: <Widget>[
              ChoiceChipWidget(chipList, (item) {
                print('Item selected: $item');
                return (item);
              }),
            ],
          ),
          RaisedButton(
            child: Text("Submit"),
            onPressed: () {

            },
          ),
         // Text(item), data should appear here
        ],
      ),
    );
  }
}

Answer 1

您可以创建一个字段selectedItem，在选择项时对其进行更新。在onPressed方法中更新状态。就像这样：

class AddCashForm extends StatefulWidget {
  @override
  _AddCashFormState createState() => _AddCashFormState();
}

class _AddCashFormState extends State<AddCashForm> {
  DateTime selectedDate = DateTime.now();
  String selectedItem;
  List<String> chipList = [
    "one",
    "two",
    "three",
    "four",
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Row(
            children: <Widget>[
              ChoiceChipWidget(chipList, (item) {
                print('Item selected: $item');
                selectedItem = item;
                return (item);
              })
            ],
          ),
          RaisedButton(
            child: Text("Submit"),
            onPressed: () {
              setState(() {});
            },
          ),
          // Text(item), data should appear here
        ],
      ),
    );
  }
}

Answer 2

如果希望项目自动更新，而不单击“提交”，请使用以下命令：

class _AddCashFormState extends State<AddCashForm> {
  final selectedDate = DateTime.now();
  final chipList = <String>[
    'one',
    'two',
    'three',
    'four',
  ];

  String item;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Row(
            children: chipList
                .map<Widget>((s) => ChoiceChip(
                      label: Text(s),
                      selected: s == item,
                      onSelected: (bool selected) {
                        setState(() {
                          item = selected ? s : null;
                        });
                      },
                    ))
                .toList(),
          ),
          Text(item ?? ''),
        ],
      ),
    );
  }
}