Flutter中如何序列化枚举列表并存储到SharedPreferences？

你遇到的错误是因为Dart默认的json.encode无法识别带有@JsonEnum和@JsonValue注解的枚举实例——这些注解是给json_serializable库用的，默认编码器不知道如何将枚举转换为可编码的JSON值。以下是两种可行的解决方案：

方案一：使用json_serializable生成序列化代码 #

这是长期维护项目的规范方式：

1. 确保pubspec.yaml依赖配置正确：

dependencies:
  json_annotation: ^4.8.1

dev_dependencies:
  build_runner: ^2.4.4
  json_serializable: ^6.7.1

2. 运行代码生成命令：

flutter pub run build_runner build

运行后会自动生成枚举的序列化/反序列化代码，每个枚举值将拥有toJson()和fromJson()方法。

3. 序列化存储枚举列表：

final preferences = await SharedPreferences.getInstance();
// 将每个枚举转换为对应的JSON值，再编码为字符串
final encodedList = stepState.map((state) => state.toJson()).toList();
await preferences.setString('stepState', json.encode(encodedList));

4. 反序列化读取：

final preferences = await SharedPreferences.getInstance();
final storedString = preferences.getString('stepState');
if (storedString != null) {
  final decodedList = json.decode(storedString) as List<String>;
  final restoredStepState = decodedList.map((s) => MyStepState.fromJson(s)).toList();
}

方案二：手动实现枚举与字符串的转换 #

如果不想依赖json_serializable，可以给枚举写扩展方法手动处理：

1. 添加枚举扩展：

extension MyStepStateConverter on MyStepState {
  // 将枚举转换为对应的JSON字符串值
  String toJsonString() {
    switch (this) {
      case MyStepState.indexed:
        return 'indexed';
      case MyStepState.editing:
        return 'editing';
      case MyStepState.complete:
        return 'complete';
      case MyStepState.disabled:
        return 'disabled';
      case MyStepState.error:
        return 'error';
    }
  }

  // 从JSON字符串值转换回枚举
  static MyStepState fromJsonString(String value) {
    switch (value) {
      case 'indexed':
        return MyStepState.indexed;
      case 'editing':
        return MyStepState.editing;
      case 'complete':
        return MyStepState.complete;
      case 'disabled':
        return MyStepState.disabled;
      case 'error':
        return MyStepState.error;
      default:
        throw ArgumentError('无效的MyStepState值: $value');
    }
  }
}

2. 存储枚举列表：

final preferences = await SharedPreferences.getInstance();
final encodedList = stepState.map((state) => state.toJsonString()).toList();
await preferences.setString('stepState', json.encode(encodedList));

3. 读取并反序列化：

final preferences = await SharedPreferences.getInstance();
final storedString = preferences.getString('stepState');
if (storedString != null) {
  final decodedList = json.decode(storedString) as List<String>;
  final restoredStepState = decodedList.map(MyStepStateConverter.fromJsonString).toList();
}

内容的提问来源于stack exchange，提问作者HelpWanted