自定义类集交叉点在DART中不起作用

Question

以下是代码：

   final Set<Item> _set1 = {
      Item(id: 1, name: "carrot"),
      Item(id: 2,name: "apple"),
      Item(id: 3,name: "mango")
   };

  final Set<Item> _set2 = {
     Item(id: 1, name: "carrot"),
   };
  print(_set1.intersection(_set2));

我的班级看起来像这样：

class Item{
  int id;
  String name;
Item({required this.id,required this.name});
}

必需的输出：

{Instance of 'Item'}
//carrot which is common

以上代码出现的输出：

{}

Answer 1

DART中的一个文字创建A

linkedhashset的元素必须具有一致的对象。== 和 object.hashcode 实现。这意味着==操作员必须在元素上定义稳定的等价关系（反射性，对称性，及时且随着时间的推移一致），并且hashcode必须相同对于被视为==的对象。

换句话说，您必须覆盖==和hashcode在item类中。

void main() {
  final Set<Item> _set1 = {
    Item(id: 1, name: "carrot"),
    Item(id: 2, name: "apple"),
    Item(id: 3, name: "mango")
  };

  final Set<Item> _set2 = {
    Item(id: 1, name: "carrot"),
  };
  print(_set1.intersection(_set2));
}

class Item {
  int id;
  String name;
  Item({required this.id, required this.name});
  
  // add an implementation for hashCode and ==
  @override
  int get hashCode => Object.hash(id, name);
  
  @override
  operator ==(Object other) =>
      other is Item && id == other.id && name == other.name;
}