Dart类需要对象==的实现。

Question

当我突然编码时，我的所有文件都变成红色，需要一个实现并删除构造函数const关键字。因此，我感到困惑的是，它是否是对dart类的更新，以要求该实现或其他什么。

​

​

​

​

下面是一个示例类：

    class Message {
      final String userId;
      final String messageText;
      final DateTime sentAt;
      DocumentReference? reference;

      Message({
        required this.userId,
        required this.messageText,
        required this.sentAt,
        this.reference,
      });

      Map<String, dynamic> toJson() => {
            'userId': userId,
            'messageText': messageText,
            'sentAt': sentAt.toString(),
          };

      factory Message.fromJson(Map<String, dynamic> json) {
        return Message(
          userId: json['userId'] ?? "",
          messageText: json['messageText'] ?? "",
          sentAt: DateTime.parse(json['sentAt'] as String),
        );
      }
      factory Message.fromSnapshot(DocumentSnapshot snapshot) {
        final message = Message.fromJson(snapshot.data() as Map<String, dynamic>);
        return message;
      }
      // Without this operator there is a compile error.
      @override
      operator ==(Object other) {
        // TODO: implement ==
        throw UnimplementedError();
      }
    }

Answer 1

您可以使用Equatable包实现相等。要使用const承包商，所有字段都必须是最终的。

class Message extends Equatable {
  final String userId;
  final String messageText;
  final DateTime sentAt;
  final DocumentReference? reference;

  const Message({
    required this.userId,
    required this.messageText,
    required this.sentAt,
    this.reference,
  });

  Map<String, dynamic> toJson() => {
        'userId': userId,
        'messageText': messageText,
        'sentAt': sentAt.toString(),
      };

  factory Message.fromJson(Map<String, dynamic> json) {
    return Message(
      userId: json['userId'] ?? "",
      messageText: json['messageText'] ?? "",
      sentAt: DateTime.parse(json['sentAt'] as String),
    );
  }
  factory Message.fromSnapshot(DocumentSnapshot snapshot) {
    final message = Message.fromJson(snapshot.data() as Map<String, dynamic>);
    return message;
  }

  @override
  List<Object?> get props => [userId, messageText, sentAt, reference];

  Message copyWith({
    String? userId,
    String? messageText,
    DateTime? sentAt,
    DocumentReference? reference,
  }) {
    return Message(
      userId: userId ?? this.userId,
      messageText: messageText ?? this.messageText,
      sentAt: sentAt ?? this.sentAt,
      reference: reference ?? this.reference,
    );
  }
}