错误：实体和 Pojo 必须有一个可用的公共构造函数 - Java

Question

每当我尝试编译应用程序时，我都会收到此错误error: Entities and Pojos must have a usable public constructor. You can have an empty constructor or a constructor whose parameters match the fields (by name and type). - java.util.ListSystemMessagesEntity.java :    @Entity(tableName = "system_messages")    @TypeConverters(ReplyMessages.class)    public class SystemMessageEntity {        @PrimaryKey        @NonNull        public String messageId;        public String title;        public String body;        public String color;        public Integer date;        public String icon;        public String ad;        public Integer isRead;        public String ip;        String id; //user_id        @Embedded(prefix = "reply_")        private List<ReplyMessage> reply_message;            @Ignore        public SystemMessageEntity() {        }            public SystemMessageEntity(String id, @NonNull String messageId, String title, String body, String color, Integer date, String icon, String ad, Integer isRead, String ip, List<ReplyMessage> reply_message) {            this.id = id;            this.messageId = messageId;            this.title = title;            this.body = body;            this.color = color;            this.date = date;            this.icon = icon;            this.ad = ad;            this.isRead = isRead;            this.ip = ip;            this.reply_message = reply_message;        }    //getters and setters}回复消息.java :@TypeConverters(ReplyMessages.class)公共类 ReplyMessage {private String body = "";private String userId = "";private Integer date = 0;private String id = "";private String messageId = "";@Ignorepublic ReplyMessage() {}public ReplyMessage(String body, String userId, Integer date, String id, String messageId) {    this.body = body;    this.date = date;    this.id = id;    this.messageId = messageId;    this.userId = userId;}

Answer 1

我已经解决了这个问题。好吧，似乎我不能将 @Embedded 与 @TypeConverter 一起使用，主要是因为转换器返回一个 String 并且它是原始类型而不是 POJO 类。无论如何，我删除了 @Embedded 注释并且它工作正常。

Answer 2

Android Room 需要一个空的构造函数，因此@Ignore从空构造函数中删除注释并将其放置在带有参数的构造函数上。

 public SystemMessageEntity() {}

 @Ignore

 public SystemMessageEntity(String id, @NonNull String messageId, ...) {

     // ... initializing the params

 }