flutter - 集添加重复的项目

Question

当我将相同的项目添加到集合中时，如果该项目包含列表，它将被复制。

例如:
‍‍‍‍

main() {
  print('equales ${Foo([]) == Foo([])}');

  Set<Foo> set = {};

  set.add(Foo([]));
  print("set.length = ${set.length}");
  set.add(Foo([]));
  print("set.length = ${set.length}");
}

class Foo {
  List<int> ints;
  Foo(this.ints);
  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is Foo &&
          runtimeType == other.runtimeType &&
          listEquals(ints, other.ints);
  @override
  int get hashCode => ints.hashCode;
}

输出:

equales true
set.length = 1
set.length = 2

Answer 1

您的代码是正确的，但是每次您将新的List []传递给Set时都使用不同的哈希码。而不是检查列表的哈希码，而是使用枚举类检查相等性。

main() {
  print('equales ${Foo([]) == Foo([])}');
  print('list -> ${[] == []}');

  Set<Foo> set = {};

  set.add(Foo([], fooType: FooType.HAPPY));
  print("set.length = ${set.length}");

  set.add(Foo([], fooType: FooType.HAPPY));
  print("set.length = ${set.length}"); 

  set.add(Foo([], fooType: FooType.SAD));
  print("set.length = ${set.length}");
}

class Foo {
  List<int> ints;
  FooType fooType;

  Foo(this.ints, {this.fooType});

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is Foo &&
          runtimeType == other.runtimeType &&
          listEquals(ints, other.ints);

  @override
  int get hashCode => fooType.hashCode;
} 

enum FooType { HAPPY, SAD }

输出:

equales true
list -> false
set.length = 1
set.length = 1
set.length = 2

希望它会有用