问Dart专用阵列

EN

//in a.dart
class A {
  int _x;
  int get x => _x;
  set x(int value) {
    bool validation_ok=true;
    //do some validation/processing
    if (validation_ok) {
      _x = value;
      //perform side effects that should happen every time _x changes e.g. save to SharedPreferences
      print('Validated $value and side effects performed');
    }
  }
}
//in amain.dart
import 'a.dart';
void main() {
  A a = A();
  a.x = 5; //if validation successful stores 5 to _x and performs side effects
  print(a.x); //prints 'Validated 5 and side effects performed' and then '5'
}

//in b.dart
class B {
  List<int> _y;
  List<int> get y => _y;
  set y(List<int> value) {
    bool validation_ok=true;
    //do some validation/processing
    if (validation_ok) {
      _y = value;
      //perform side effects that should happen every time _y changes e.g. save to SharedPreferences
      print('Validated $value and side effects performed');
    }
  }
}
//in bmain.dart
import 'b.dart';
void main() {
  B b = B();
  b.y = [5]; //if validation successful stores [5] to _y and performs side effects
  print(b.y); //prints 'Validated [5] and side effects performed' and '[5]'
  b.y.add(6); //now _y is [5,6] but no validation was done on 6 and no side effects performed
  print(b.y); //prints '[5,6]' only
}