Flutter - DropdownButtonFormField值未更新

Question

在关闭并重新打开AlertDialog框之前，我的下拉按钮值不会更新。

我将变量设置在我的班级顶部

class _ItemListState extends State<ItemList> {
  int _ratingController;
...

}

在类中我有一个打开表单的AlertDialog，在这里我有DropdownButtonFormField

AlertDialog(
      content: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          TextField(
            controller: _eateryController,
            autofocus: true,
            decoration:
                InputDecoration(labelText: 'Eatery', hintText: 'eg Pizza Hut'),
          ),
          TextField(
            controller: _supplierController,
            decoration: InputDecoration(
                labelText: 'Supplier', hintText: 'eg Deliveroo'),
          ),
          TextField(
            controller: _descriptionController,
            decoration: InputDecoration(
                labelText: 'Description', hintText: 'eg cheese pizza'),
          ),
          DropdownButtonFormField<int>(
            value: _ratingController,
            items: [1, 2, 3, 4, 5]
                .map((label) => DropdownMenuItem(
                      child: Text(label.toString()),
                      value: label,
                    ))
                .toList(),
            hint: Text('Rating'),
            onChanged: (value) {
              setState(() {
                _ratingController = value;
              });
            },
          ),
        ],
      ),
      actions: <Widget>[
        FlatButton(
          onPressed: () {
            _handleSubmit(_eateryController.text, _supplierController.text,
                _descriptionController.text, _ratingController);
            Navigator.pop(context);
          },
          child: Text('Save'),
        ),
        FlatButton(
          onPressed: () => Navigator.pop(context),
          child: Text('Cancel'),
        )
      ],
    );

setState似乎没有动态更新字段值。只有关闭并重新打开AlertDialog后，才会显示更新后的值。

如何才能立即更新？

谢谢

Answer 1

你需要创建一个新的StatefulWidget类，它应该返回你的AlertDialog

class MyDialog extends StatefulWidget {
  @override
  _MyDialogState createState() => _MyDialogState();
}

class _MyDialogState extends State<MyDialog> {
  int _ratingController;

  @override
  Widget build(BuildContext context) {
    return AlertDialog(
      content: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          TextField(
            controller: _eateryController,
            autofocus: true,
            decoration:
            InputDecoration(labelText: 'Eatery', hintText: 'eg Pizza Hut'),
          ),
          TextField(
            controller: _supplierController,
            decoration: InputDecoration(
                labelText: 'Supplier', hintText: 'eg Deliveroo'),
          ),
          TextField(
            controller: _descriptionController,
            decoration: InputDecoration(
                labelText: 'Description', hintText: 'eg cheese pizza'),
          ),
          DropdownButtonFormField<int>(
            value: _ratingController,
            items: [1, 2, 3, 4, 5]
                .map((label) => DropdownMenuItem(
              child: Text(label.toString()),
              value: label,
            ))
                .toList(),
            hint: Text('Rating'),
            onChanged: (value) {
              setState(() {
                _ratingController = value;
              });
            },
          ),
        ],
      ),
      actions: <Widget>[
        FlatButton(
          onPressed: () {
            _handleSubmit(_eateryController.text, _supplierController.text,
                _descriptionController.text, _ratingController);
            Navigator.pop(context);
          },
          child: Text('Save'),
        ),
        FlatButton(
          onPressed: () => Navigator.pop(context),
          child: Text('Cancel'),
        )
      ],
    );
  }
}

---

像这样使用它

showDialog(
  context: context,
  builder: (context) {
    return MyDialog();
  },
);

Answer 2

看起来你在一个错误的小部件中调用setState。 AlertDialog不属于ItemList的树，因为它位于另一个Route内。所以在setState内部调用_ItemListState不会重建AlertDialog。

考虑将AlertDialog的内容分成单独的StatefulWidget并将int _ratingController放入其状态。