android - 在 Flutter 中为 DropdownMenu 使用枚举和 ValueNotifier

Question

您好，我的目标是在下拉菜单中显示枚举值，并将 setState 替换为 ValueNotifier 和 ValueListenableBuilder。我对 flutter 还很陌生，目前我只知道当我们有一个字符串列表及其使用 setState 时如何显示下拉菜单，但我该如何修改它。因此，例如我们有 enum Locations={belgium,germany,spain, etc}

到目前为止，这是我的代码:

class _TestState extends State<Test> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('hi'),
      ),
      drawer: FoodNotifyDrawer('name'),
      body: Container(
        padding: EdgeInsets.all(7),
        child: Center(
          child: Column(
            children: [
              SizedBox(
                height: 40,
              ),
              DropdownButton(
                // Not necessary for Option 1
                value: _selectedLocation,
                onChanged: (String? newValue) {
                  setState(() {
                    _selectedLocation = newValue;
                  });
                },
                items: _locations.map((location) {
                  return DropdownMenuItem(
                    child: Text(location),
                    value: location,
                  );
                }).toList(),
              ),
              SizedBox(
                height: 40,
              ),
              Text('Option 2'),
              SizedBox(
                height: 40,
              ),
            ],
          ),
        ),
      ),
    );
  }
}

任何帮助都会很棒，提前致谢:)

Answer 1

import 'package:flutter/material.dart';

enum Locations { belgium, germany, spain }

class DropDownTest extends StatelessWidget {
DropDownTest({Key? key}) : super(key: key);
final ValueNotifier<Locations> _selectedValue =
  ValueNotifier<Locations>(Locations.belgium);
@override
Widget build(BuildContext context) {
return Scaffold(
  body: Center(
    child: ValueListenableBuilder<Locations>(
        valueListenable: _selectedValue,
        builder: (context, v, _) {
          return DropdownButton<Locations>(
            value: v,
            onChanged: (Locations? newValue) {
              if (newValue != null) {
                _selectedValue.value = newValue;
              }
            },
            items: Locations.values.map((d) {
              return DropdownMenuItem(
                child: Text(d.name),
                value: d,
              );
            }).toList(),
          );
        }),
      ),
    );
    }
   }