Add methods or values to enum in dart

Question

In java when you are defining an enum you can do something similar to the following. Is this possible in Dart?

enum blah {
  one(1), two(2);
  final num valu         


        

Answer 1

I did this (inspired form the accepted answer by @vovahost)

enum CodeVerifyFlow{
  SignUp, Recovery, Settings
}

extension CatExtension on CodeVerifyFlow {
  String get name {
    return ["sign_up", "recovery", "settings"][this.index];
  }
}

// use it like
CodeVerifyFlow.SignUp.name

thank me later!

Answer 2

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

Answer 3

It may not be "Effective Dart" , I add a static method inside a Helper class ( there is no companion object in Dart) .

In your color.dart file

enum Color {
  red,
  green,
  blue
}

class ColorHelper{

  static String getValue(Color color){
    switch(color){
      case Color.red: 
        return "Red";
      case Color.green: 
        return "Green";
      case Color.blue: 
        return "Blue";  
      default:
        return "";
    }
  }

}

Since the method is in the same file as the enum, one import is enough

import 'package:.../color.dart';

...
String colorValue = ColorHelper.getValue(Color.red);

Answer 4

As an improvement on the other suggestions of using Extensions, you can define your assigned values in a list of map, and the extension will be concise.

enum Numbers {
  one,
  two,
  three,
}

// Numbers.one.value == 1

example with list

extension NumbersExtensionList on Numbers {
  static const values = [1, 2, 3];
  int get value => values[this.index];
}

example with map

extension NumbersExtensionMap on Numbers {
  static const valueMap = const {
    Numbers.one: 1,
    Numbers.two: 2,
    Numbers.three: 2,
  };
  int get value => valueMap[this];
}

Note: This approach has the limitation that you can not define a static factory method on the Enum, e.g. Numbers.create(1) (as of Dart 2.9). You can define this method on the NumbersExtension, but it would need to be called like NumbersExtension.create(1)

Answer 5

For String returns :

enum Routes{
  SPLASH_SCREEN,
  HOME,
  // TODO Add according to your context
}

String namedRoute(Routes route){
  final runtimeType = '${route.runtimeTypes.toString()}.';
  final output = route.toString();
  return output.replaceAll(runtimeType, "");
}

Answer 6

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