Setter in Dart

Setter In Dart

Setter is used to set the value of a property. It is mostly used to update a private property’s value. Setter provide explicit write access to an object properties.

Syntax

set property_name (value) {
  // Setter body
}

Info

Note: Instead of writing { } after the property name, you can also write => (fat arrow) after the property name.

Example 1: Setter In Dart

In this example below, there is a class named NoteBook. The class has two private properties _name and _prize. There are two setters name and price to update the value of the properties. There is also a method display to display the value of the properties.

class NoteBook {
  // Private Properties
  String? _name;
  double? _prize;

  // Setter to update private property _name
  set name(String name) => this._name = name;

  // Setter to update private property _prize
  set price(double price) => this._prize = price;

  // Method to display the values of the properties
  void display() {
    print("Name: ${_name}");
    print("Price: ${_prize}");
  }
}

void main() {
  // Create an object of NoteBook class
  NoteBook nb = new NoteBook();
  // setting values to the object using setter
  nb.name = "Dell";
  nb.price = 500.00;
  // Display the values of the object
  nb.display();
}

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Info

Note: In the above example, a setter name and price are used to update the value of the properties _name and _prize.

Example 2: Setter In Dart With Data Validation

In this example, there is a class named NoteBook. The class has two private properties _name and _prize. If the value of _prize is less than 0, we will throw an exception. There are also two setters name and price to update the value of the properties. The class also has a method display() to display the values of the properties.

class NoteBook {
  // Private properties
  String? _name;
  double? _prize;

  // Setter to update the value of name property
  set name(String name) => _name = name;

  // Setter to update the value of price property
  set price(double price) {
    if (price < 0) {
      throw Exception("Price cannot be less than 0");
    }
    this._prize = price;
  }

  // Method to display the values of the properties
  void display() {
    print("Name: $_name");
    print("Price: $_prize");
  }
}

void main() {
  // Create an object of NoteBook class
  NoteBook nb = new NoteBook();
  // setting values to the object using setter
  nb.name = "Dell";
  nb.price = 250;

  // Display the values of the object
  nb.display();
}

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Info

Note: It is generally best to not allow the user to set the value of a field directly. Instead, you should provide a setter method that can validate the value before setting it. This is very important when working on large and complex programs.

Example 3: Setter In Dart

In this example, there is a class named Student. The class has two private properties _name and _classnumber. We will also create two setters name and classnumber to update the value of the properties. The classnumber setter will only accept a value between 1 and 12. The class also has a method display() to display the values of the properties.

class Student {
  // Private properties
  String? _name;
  int? _classnumber;

  // Setter to update the value of name property
  set name(String name) => this._name = name;

  // Setter to update the value of classnumber property
  set classnumber(int classnumber) {
    if (classnumber <= 0 || classnumber > 12) {
      throw ('Classnumber must be between 1 and 12');
    }
    this._classnumber = classnumber;
  }

  // Method to display the values of the properties
  void display() {
    print("Name: $_name");
    print("Class Number: $_classnumber");
  }
}
void main() {
  // Create an object of Student class
  Student s = new Student();
  // setting values to the object using setter
  s.name = "John Doe";
  s.classnumber = 12;

  // Display the values of the object
  s.display();

  // This will generate error
  //s.setClassNumber(13);
}

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Why Is Setter Important?

It is used to set the value of a private property.
It is also used for data validation.
It gives you better control over the data.

Video

Watch our video on setters in Dart.

Challenge

Try to create a class named University with two private properties _name and _year. The class will also have two setters name and year to update the value of the properties. The year setter will only accept a value between 1900 and 2023. Also, create a method display() to display the values of the properties.