Dart/Flutter中如何从列表中移除符合指定属性条件的对象

你当前写法的核心问题是：Dart中List.contains、List.remove默认判断的是对象引用相等，你每次调用{teacherId, index}都会创建一个新的Set实例，哪怕值和列表中已存的元素完全一致，也会因为不是同一个对象实例判定为不匹配，所以逻辑永远走不到删除分支。

方案1：直接遍历匹配值（无需修改现有存储结构） #

用indexWhere方法遍历列表匹配两个属性的值，找到对应下标后直接移除：

void addTeacher(int teacherId, int index) {
  // 查找匹配元素的下标，匹配成功返回>=0的下标，失败返回-1
  final matchIndex = selectedList.indexWhere((item) => 
    item.contains(teacherId) && item.contains(index)
  );

  if (matchIndex != -1) {
    selectedList.removeAt(matchIndex);
    myColor = Colors.grey;
    print('removed teacher => $teacherId');
  } else {
    selectedList.add({teacherId, index});
    myColor = AsasColors().blue;
    print('added teacher => $teacherId');
  }

  notifyListeners();
  print(selectedList);
}

注意：你当前用{teacherId, index}存储的是Set类型，是无序无重复的集合，如果要明确存储带字段名的结构化数据，更推荐用Map格式{'teacherId': teacherId, 'index': index}，对应的匹配逻辑改为：

final matchIndex = selectedList.indexWhere((item) => 
  item['teacherId'] == teacherId && item['index'] == index
);

方案2：自定义类（更规范的生产环境写法） #

定义专门的实体类，重写==运算符和hashCode，之后就可以直接用contains、remove方法进行值匹配，代码更易维护：

// 定义实体类
class TeacherItem {
  final int teacherId;
  final int index;

  TeacherItem({required this.teacherId, required this.index});

  // 重写相等判断逻辑，只要id和index都相等就判定为同一个对象
  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is TeacherItem &&
          runtimeType == other.runtimeType &&
          teacherId == other.teacherId &&
          index == other.index;

  @override
  int get hashCode => teacherId.hashCode ^ index.hashCode;
}

修改后的业务逻辑代码：

// selectedList的类型改为List<TeacherItem>
void addTeacher(int teacherId, int index) {
  final target = TeacherItem(teacherId: teacherId, index: index);
  if (selectedList.contains(target)) {
    selectedList.remove(target);
    myColor = Colors.grey;
    print('removed teacher => $teacherId');
  } else {
    selectedList.add(target);
    myColor = AsasColors().blue;
    print('added teacher => $teacherId');
  }
  notifyListeners();
  print(selectedList);
}

内容的提问来源于stack exchange，提问作者Faris Shomali