Iterator Example in Dart

fruits-iterator.dart

// A `Fruit` object contains `name` and `color`
class Fruit {
  final String name;
  final String color;
  
  Fruit( this.name, this.color );
}

// A `Fruits` collection contains the List of `Fruit` object
// `iterator` getter returns an instance of `FruitsIterator` instance
class Fruits {
  List<Fruit> fruits = [];
  
  Fruits( this.fruits );
  
  FruitsIterator get iterator {
    return FruitsIterator( this.fruits );
  }
}

// `FruitsIterator` walks through a List of `Fruit` object
// and returns `String` values, hence it must extend `Iterator<String>` class
class FruitsIterator extends Iterator<String> {
  List<Fruit> fruits = [];
  String _current;
  int index = 0;
  
  FruitsIterator( this.fruits );
  
  // `oveNext`method must return boolean value to state if next value is available
  bool moveNext() {
    if( index == fruits.length ) {
      _current = null;
      return false;
    } else {
      _current = fruits[ index++ ].name;
      return true;
    }
  }
  
  // `current` getter method returns the current value of the iteration when `moveNext` is called
  String get current => _current;
}

void main() {
  
  // create `Fruits` from a List of `Fruit` objects
  var fruits = Fruits([
    Fruit( 'Banana', 'Green' ),
    Fruit( 'Mango', 'Yellow' ),
    Fruit( 'Apple', 'Red' )
  ]);
  
  // get an iterator from Fruits object
  var iterator = fruits.iterator;
  
  // walk through iterator using `moveNext()` method and `current` getter
  while( iterator.moveNext() ) {
    print( 'Fruit name: ${ iterator.current }' );
  }
  
  // Result:
  // Fruit name: Banana
  // Fruit name: Mango
  // Fruit name: Apple
  
  // Iterator Doc: https://api.dartlang.org/stable/2.6.1/dart-core/Iterator-class.html
  // Iterable Doc: https://api.dartlang.org/stable/2.6.1/dart-core/Iterable-class.html
}