flutter：如何在共享偏好中保留枚举？

Question

我正在通过我的应用程序使用枚举，我注意到每次我离开页面时它都会重置，或者当然当我关闭应用程序时，我知道共享首选项，但我不知道这是否是正确的方法或实际上如何实现它带有一个枚举。任何有关这方面的信息将不胜感激，这里是我的应用程序的示例：

`enum Gender {
  male,
  female,
}

class InputPage extends StatefulWidget {
  @override
  _InputPageState createState() => _InputPageState();
}

class _InputPageState extends State<InputPage> {
  Gender selectedGender;
  int height = 180;
  int weight = 60;
  int age = 20;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('BMI CALCULATOR'),
      ),
      body: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: <Widget>[
          Expanded(
              child: Row(
            children: <Widget>[
              Expanded(
                child: ReusableCard(
                  onPress: () {
                    setState(() {
                      selectedGender = Gender.male;
                    });
                  },
                  colour: selectedGender == Gender.male
                      ? kActiveCardColour
                      : kInactiveCardColour,
                  cardChild: IconContent(
                    icon: FontAwesomeIcons.mars,
                    label: 'MALE',
                  ),
                ),
              ),
              Expanded(
                child: ReusableCard(
                  onPress: () {
                    setState(() {
                      selectedGender = Gender.female;
                    });
                  },
                  colour: selectedGender == Gender.female
                      ? kActiveCardColour
                      : kInactiveCardColour,
                  cardChild: IconContent(
                    icon: FontAwesomeIcons.venus,
                    label: 'FEMALE',
                  ),
                ),
              ),
            ],
          ))

,`

Answer 1

您可以复制粘贴运行下面的完整代码
您可以使用包https://pub.dev/packages/enum_to_string 保存并获取enum步骤String
1: init selectedGenderin initState()withEnumToString.fromString

@override
  void initState() {
    WidgetsBinding.instance.addPostFrameCallback((_) {
      initGender();
    });
    super.initState();
  }

  void initGender() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    selectedGender =
        EnumToString.fromString(Gender.values, prefs.getString("gender"));
    setState(() {});
  }

第 2 步：保存selectedGender为prefs.setString("gender", enumToString.parse(Gender.male));

    onPress: () async {
            setState(() {
              selectedGender = Gender.male;
            });
            SharedPreferences prefs =
                await SharedPreferences.getInstance();
            prefs.setString(
                "gender", EnumToString.parse(Gender.male));
          }

工作演示

完整代码

import 'package:flutter/material.dart';
import 'package:enum_to_string/enum_to_string.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:font_awesome_flutter/font_awesome_flutter.dart';

const kBottomContainerHeight = 80.0;
const kActiveCardColour = Color(0xFF1D1E33);
const kInactiveCardColour = Color(0xFF111328);
const kBottomContainerColour = Color(0xFFEB1555);

const kLabelTextStyle = TextStyle(
  fontSize: 18.0,
  color: Color(0xFF8D8E98),
);

const kNumberTextStyle = TextStyle(
  fontSize: 50.0,
  fontWeight: FontWeight.w900,
);

const kLargeButtonTextStyle = TextStyle(
  fontSize: 25.0,
  fontWeight: FontWeight.bold,
);

const kTitleTextStyle = TextStyle(
  fontSize: 50.0,
  fontWeight: FontWeight.bold,
);

const kResultTextStyle = TextStyle(
  color: Color(0xFF24D876),
  fontSize: 22.0,
  fontWeight: FontWeight.bold,
);

const kBMITextStyle = TextStyle(
  fontSize: 100.0,
  fontWeight: FontWeight.bold,
);

const kBodyTextStyle = TextStyle(
  fontSize: 22.0,
);

class IconContent extends StatelessWidget {
  IconContent({this.icon, this.label});

  final IconData icon;
  final String label;

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Icon(
          icon,
          size: 80.0,
        ),
        SizedBox(
          height: 15.0,
        ),
        Text(
          label,
          style: kLabelTextStyle,
        )
      ],
    );
  }
}

enum Gender {
  male,
  female,
}

class ReusableCard extends StatelessWidget {
  ReusableCard({@required this.colour, this.cardChild, this.onPress});

  final Color colour;
  final Widget cardChild;
  final Function onPress;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: onPress,
      child: Container(
        child: cardChild,
        margin: EdgeInsets.all(15.0),
        decoration: BoxDecoration(
          color: colour,
          borderRadius: BorderRadius.circular(10.0),
        ),
      ),
    );
  }
}

class InputPage extends StatefulWidget {
  @override
  _InputPageState createState() => _InputPageState();
}

class _InputPageState extends State<InputPage> {
  Gender selectedGender;
  int height = 180;
  int weight = 60;
  int age = 20;

  @override
  void initState() {
    WidgetsBinding.instance.addPostFrameCallback((_) {
      initGender();
    });
    super.initState();
  }

  void initGender() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    selectedGender =
        EnumToString.fromString(Gender.values, prefs.getString("gender"));
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text('BMI CALCULATOR'),
        ),
        body: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: <Widget>[
              Expanded(
                  child: Row(
                children: <Widget>[
                  Expanded(
                    child: ReusableCard(
                      onPress: () async {
                        setState(() {
                          selectedGender = Gender.male;
                        });
                        SharedPreferences prefs =
                            await SharedPreferences.getInstance();
                        prefs.setString(
                            "gender", EnumToString.parse(Gender.male));
                      },
                      colour: selectedGender == Gender.male
                          ? kActiveCardColour
                          : kInactiveCardColour,
                      cardChild: IconContent(
                        icon: FontAwesomeIcons.mars,
                        label: 'MALE',
                      ),
                    ),
                  ),
                  Expanded(
                    child: ReusableCard(
                      onPress: () async {
                        setState(() {
                          selectedGender = Gender.female;
                        });
                        SharedPreferences prefs =
                            await SharedPreferences.getInstance();
                        prefs.setString(
                            "gender", EnumToString.parse(Gender.female));
                      },
                      colour: selectedGender == Gender.female
                          ? kActiveCardColour
                          : kInactiveCardColour,
                      cardChild: IconContent(
                        icon: FontAwesomeIcons.venus,
                        label: 'FEMALE',
                      ),
                    ),
                  ),
                ],
              ))
            ]));
  }
}

Future<void> main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: InputPage(),
    );
  }
}