Add methods or values to enum in dart

Starting with Dart 2.6 you can define extensions on classes (Enums included).

enum Cat {
  black,
  white
}

extension CatExtension on Cat {

  String get name {
    switch (this) {
      case Cat.black:
        return 'Mr Black Cat';
      case Cat.white:
        return 'Ms White Cat';
      default:
        return null;
    }
  }

  void talk() {
    print('meow');
  }
}

Example:

Cat cat = Cat.black;
String catName = cat.name;
cat.talk();

Here's one more live example (uses a constant map instead of a switch): https://dartpad.dartlang.org/c4001d907d6a420cafb2bc2c2507f72c

Dart enums are used only for the simplest cases. If you need more powerful or more flexible enums, use classes with static const fields like shown in https://stackoverflow.com/a/15854550/217408

This way you can add whatever you need.

Nope. In Dart, enums can only contain the enumerated items:

enum Color {
  red,
  green,
  blue
}

However, each item in the enum automatically has an index number associated with it:

print(Color.red.index);    // 0
print(Color.green.index);  // 1

You can get the values by their index numbers:

print(Color.values[0] == Color.red);  // True

See: https://www.dartlang.org/guides/language/language-tour#enums