Flutter中如何利用Enhanced Enum实现JSON值映射

你可以通过在增强枚举内部添加静态方法或者静态映射表来实现JSON值到枚举实例的映射，以下是具体修改方案：

方案1：添加静态fromValue方法 #

直接在MyEnhancedEnum中实现一个静态方法，遍历枚举值匹配对应的字符串：

enum MyEnhancedEnum {
  valueOne("One"),
  valueTwo("Two"),
  valueUnknown("");

  const MyEnhancedEnum(this.value);
  final String value;

  // 根据JSON字符串值返回对应的枚举，匹配失败则返回unknown
  static MyEnhancedEnum fromValue(String? value) {
    return MyEnhancedEnum.values.firstWhere(
      (enumValue) => enumValue.value == value,
      orElse: () => MyEnhancedEnum.valueUnknown,
    );
  }
}

随后在MyObject.fromJson中直接调用该方法：

factory MyObject.fromJson(Map<String, dynamic> json) => MyObject(
      myProperty: MyEnhancedEnum.fromValue(json["JSONPropertyValue"]),
    );

方案2：添加静态映射表 #

和你之前普通枚举的实现逻辑类似，但把映射表集成到增强枚举内部，提升代码内聚性：

enum MyEnhancedEnum {
  valueOne("One"),
  valueTwo("Two"),
  valueUnknown("");

  const MyEnhancedEnum(this.value);
  final String value;

  // 静态映射表：JSON字符串值 -> 对应枚举实例
  static final Map<String, MyEnhancedEnum> valueMap = {
    "One": MyEnhancedEnum.valueOne,
    "Two": MyEnhancedEnum.valueTwo,
    "": MyEnhancedEnum.valueUnknown,
  };
}

在fromJson中直接通过映射表取值，配合空值判断兜底：

factory MyObject.fromJson(Map<String, dynamic> json) => MyObject(
      myProperty: MyEnhancedEnum.valueMap[json["JSONPropertyValue"]] ?? MyEnhancedEnum.valueUnknown,
    );

完整修改后的代码示例 #

List<MyObject?>? objects = List<MyObject?>.from(json["MyObject"]!.map((x) => MyObject.fromJson(x)));

class MyObject {
  MyObject({
    this.myProperty,
  });

  MyEnhancedEnum? myProperty = MyEnhancedEnum.valueUnknown;

  factory MyObject.fromJson(Map<String, dynamic> json) => MyObject(
        myProperty: MyEnhancedEnum.fromValue(json["JSONPropertyValue"]),
      );
}

enum MyEnhancedEnum {
  valueOne("One"),
  valueTwo("Two"),
  valueUnknown("");

  const MyEnhancedEnum(this.value);
  final String value;

  static MyEnhancedEnum fromValue(String? value) {
    return MyEnhancedEnum.values.firstWhere(
      (enumValue) => enumValue.value == value,
      orElse: () => MyEnhancedEnum.valueUnknown,
    );
  }
}

内容的提问来源于stack exchange，提问作者Florentin Lupascu