Parse enum from json

Question

I have an enum

enum Mode { standard, relative, fixed }

extension ModeMap on Mode {
  static const valueMap = {
    Mode.standard: "standard",
    Mode.relative: "relative",
    Mode.fixed: "fixed",
  };
  String? get value => valueMap[this];
}

And a model using this enum with a method fromJson:

class Settings {
  Mode mode;
  String name;

  Settings({
    required this.mode,
    required this.name,
  });

  Settings.fromJson(Map<String, dynamic> json)
      : mode = Mode[json['Mode'].toString()] as Mode,
        name = json['Name'],


  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    data['Mode'] = mode.value;
    data['Name'] = name;
    return data;
  }
}

However, it seems that I can't transform the values from json to my enum this way. What is the proper way to do this?

Solution

You could do the reverse of what you did with the value getter. The following code makes a fromString method to get a Mode from a String by reversing your valueMap. You then can use it with ModeMap.fromString(json['Mode']) in your factory constructor.

enum Mode { standard, relative, fixed }

extension ModeMap on Mode {
  static const valueMap = {
    Mode.standard: "standard",
    Mode.relative: "relative",
    Mode.fixed: "fixed",
  };
  String? get value => valueMap[this];
  
  static Mode fromString(String input) {
    final reverseValueMap = valueMap.map<String, Mode>((key, value) => MapEntry(value, key));
    
    Mode? output = reverseValueMap[input];
    if(output == null) {
      throw 'Invalid String Input';
    }
    
    return output;
  }
}

class Settings {
  Mode mode;
  String name;

  Settings({
    required this.mode,
    required this.name,
  });

  Settings.fromJson(Map<String, dynamic> json)
      : mode = ModeMap.fromString(json['Mode']),
        name = json['Name'];


  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    data['Mode'] = mode.value;
    data['Name'] = name;
    return data;
  }
}