Programming in Dart: Classes

Jun 28 2022 · Dart 2.17, Flutter 3.0, DartPad

Part 1: Understand Classes

04. Write a Constructor

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Previous episode: 03. Challenge: Create a Custom Class Next episode: 05. Challenge: Define a Constructor

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So far, we’ve been creating objects and then setting up values after the fact. This can lead to cases where you might operate on an object before setting it. Now you can promise yourself to be vigilant, but you’re just setting yourself up for an error. Thankfully, we can use a constructor.

class User {
  int id = 0;
  String name = '';
}

var user = User()
..name = 'Ray'
..id = 42;

User(int id, String name) {
    this.id = id;
    this.name = name;
}

User(int id, String name) {
    id = id;
    name = name;
}

var user = User(42, 'ray');
print(user.id);

User(int id, String name) {
    this.id = id;
    this.name = name;
}

User(this.id, this.name);

User(this.id, this.name) { 
    print('this space for rent');
}

var user2 = User();

class User {
  final int id;
  final String name;
  
  User(this.id, this.name);
  
}