Dart getters and setters

#flutter #dart #getter #setter

Prerequisites

You will need basic knowledge of

Dart
Object-Oriented Programming

Getters and setters are special methods that provide read and write access to an object’s properties. Each instance variable of your class has an implicit getter, and a setter if needed. In dart, you can take this even further by implementing your own getters and setters. If you've had any experience in Object-Oriented Programming you'll feel right at home. Let's get started.

In OOP a class acts as an Abstract Data Type(ADT) for an instance of that class(Object). In dart, this is also the case. The basic syntax for a class is:

class className {
 fields;
 getters/setters
 constructor
 methods/functions
}

The getters and setters can also be placed after the constructor. Now let's create a class and instantiate it.

class Vehicle {
  String make;
  String model;
  int manufactureYear;
  int vehicleAge;
  String color;

  int get age {
    return vehicleAge;
  }

  void set age(int currentYear) {
    vehicleAge = currentYear - manufactureYear;
  }

  // We can also eliminate the setter and just use a getter.
  //int get age {
  //  return DateTime.now().year - manufactureYear;
  //}

  Vehicle({this.make,this.model,this.manufactureYear,this.color,});
}

Age here is both a getter and a setter. Let's see how we can use it.

void main() {
 Vehicle car = 
 Vehicle(make:"Honda",model:"Civic",manufactureYear:2010,color:"red");
  print(car.make); // output - Honda
  print(car.model); // output - Civic
  car.age = 2019;
  print(car.age); // output - 9

}

One of my favourite ways of using getters is getting a Map from an object.

void main() {
 Vehicle car = Vehicle(make:"Honda",model:"Civic",manufactureYear:2010,color:"red");
  print(car.map); // output - {make: Honda, model: Civic, manufactureYear: 2010, color: red}
}
class Vehicle {
  String make;
  String model;
  int manufactureYear;
  int vehicleAge;
  String color;



  Map<String,dynamic> get map {
    return {
      "make": make,
      "model": model,
      "manufactureYear":manufactureYear,
      "color": color,
    };
  }

  int get age {
    return DateTime.now().year - manufactureYear;
  }

  void set age(int currentYear) {
    vehicleAge = currentYear - manufactureYear;
  }

  Vehicle({this.make,this.model,this.manufactureYear,this.color,});
}

That covers basic usage of getter and setters in Dart. There's is a lot more to learn about classes. I will cover everything in a future post. Also, note the use of named parameters in our constructors. I'll also cover those and other ways of passing parameters in a future post

Top comments (10)

Manuel Alejandro Gamboa Jimenez • Mar 3 '22 • Edited

You should never use this.argument (formals) in constructors, what's the point of constructor arguments if you are going to assign it directly to properties?, what you should do in most cases is to use setters to validate the data passed to constructor, if you don't validate then using constructor arguments is a waste of time and just duplicated code:

class Human {
  int _age;

  Human(int age) {
    setAge(age);
  }

  void setAge(int value) {
    //an age of 0 or less is invalid, 130 years or more is invalid
    if(value <= 0 || value >= 130) { 
      //throw error 
    }

    _age = value;
  }
}

Newton Munene • Mar 9 '22

Hello. Thank you so much for the feedback.

I agree with you.

I wrote this quite a while back when I was just getting started with Dart and I have learnt quite a few things since then. Most of these articles are due for an update.

Huholoman • Dec 25 '22 • Edited

This is misleading. In domain/business entities yes (or other value object from this layer), but for example when you have db entity, you dont want validate anything here. It adds duplicit valiation for data, which were already validated and when you decide to change the validation rules, you have to change it on multiple places.

Another thing is that immutability is considered as good practice (again in domain/business layer; database entities can have some data related to performance improvements for example), that means you dont have any setter methods, just copyWith method, which calls constructor.. and in this case you can have you validation logic in constructor and there is no need for even private method. Sure you can split validation to multiple methods if the logic gets bigger.