Define Interfaces and Share Class Members through Mixins in Dart

In this lesson, we will cover Interfaces and Mixins. Interfaces act as a contract containing properties and methods that a class must define once it “implements” this interface. Mixins are Dart’s way of sharing properties and methods from multiple classes, since by design Dart adopts a single-inheritance model.

Abstract class:

void main() {
  var pixel = Phone('Pixel XL', 'HTC');
  pixel.getDeviceInfo();
}
 
abstract class Device {
  String name;
  String manufacturer;
  void getDeviceInfo();
}
 
class Phone implements Device {
  String name;
  String manufacturer;
   
  void getDeviceInfo() => print('''
  ===
  Device name: $name
  Manufactured by: $manufacturer
  ''');
   
  Phone(this.name, this.manufacturer);
}

Define a mixin:

mixin FeaturesMixin {
  bool blueTooth = true;
  bool dualSim = false;
  bool nfc = true;
}

Extends a mixin:

// Extends FeaturesMixin
mixin UtilitiesMixin on FeaturesMixin {
  bool calculator = true;
  bool flashlight = true;
  bool thermometer = false;
  
  String _has(bool feat) => feat ? 'Yes': 'No';
  
  void getAllFeatures() => print('''
  --FEATURES--
  
  Bluetooth: ${_has(super.blueTooth)}
  Dual SIM: ${_has(super.dualSim)}
  NFC: ${_has(super.nfc)}
  Calculator: ${_has(calculator)}
  Flashlight: ${_has(flashlight)}
  Thermometer: ${_has(thermometer)}
  ===
  ''');
}

use Mixin:

class Phone with FeaturesMixin, UtilitiesMixin implements Device {

void main() {
  var pixel = Phone('Pixel XL', 'HTC');
  pixel.getDeviceInfo();
  pixel.getAllFeatures(); 
/*

  ===
  Device name: Pixel XL
  Manufactured by: HTC
  
  --FEATURES--
  
  Bluetooth: Yes
  Dual SIM: No
  NFC: Yes
  Calculator: Yes
  Flashlight: Yes
  Thermometer: No
  ===
  
*/
}

mixin FeaturesMixin {
  bool blueTooth = true;
  bool dualSim = false;
  bool nfc = true;
}

// Extends FeaturesMixin
mixin UtilitiesMixin on FeaturesMixin {
  bool calculator = true;
  bool flashlight = true;
  bool thermometer = false;
  
  String _has(bool feat) => feat ? 'Yes': 'No';
  
  void getAllFeatures() => print('''
  --FEATURES--
  
  Bluetooth: ${_has(super.blueTooth)}
  Dual SIM: ${_has(super.dualSim)}
  NFC: ${_has(super.nfc)}
  Calculator: ${_has(calculator)}
  Flashlight: ${_has(flashlight)}
  Thermometer: ${_has(thermometer)}
  ===
  ''');
}

abstract class Device {
  String name;
  String manufacturer;
  void getDeviceInfo();
}

class Phone with FeaturesMixin, UtilitiesMixin implements Device {
  String name;
  String manufacturer;
  
  void getDeviceInfo() => print('''
  ===
  Device name: $name
  Manufactured by: $manufacturer
  ''');
  
  Phone(this.name, this.manufacturer);
}