Android中在使用Room时提示：Cannot figure out how to save this field into database. You can consider adding a type converter for

场景

在Android中使用Room进行存储数据库时提示:

Cannot figure out how to save this field into database. You can consider adding a type converter for

注：

博客：
https://blog.csdn.net/badao_liumang_qizhi
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实现

这是因为Room中不支持对象中直接存储集合。

下面是要存储的对象Bean

@Entity
public class ChatBean {
    private String msg;
    private int code;
    @NonNull
    @PrimaryKey
    private String id = "";
    private List<ChatItem> data;

    @Entity
    public static class ChatItem {

        @PrimaryKey
        private int id;
        private String msgNum;
        private String content;
        //语音消息服务器地址
        private String remoteContent;
        private String sender;
        private String receiver;
        private String type;
        private boolean canReceived;
        private String sendTime;
        private String receivedTime;
        //语音时长
        private int voiceDuration;
        private boolean isRead;

    }

}

上面省略了get和set方法，在bean中还有个 对象集合data,对象为ChatItem

所以需要新建一个转换类ChatItemConverter

名字根据自己业务去定

package com.bdtd.bdcar.database;

import androidx.room.TypeConverter;

import com.bdtd.bdcar.bean.ChatBean;
import com.bdtd.bdcar.common.GsonInstance;
import com.google.gson.reflect.TypeToken;

import java.lang.reflect.Type;
import java.util.List;

public class ChatItemConverter {

    @TypeConverter
    public String objectToString(List<ChatBean.ChatItem> list) {
        return GsonInstance.getInstance().getGson().toJson(list);
    }

    @TypeConverter
    public List<ChatBean.ChatItem> stringToObject(String json) {
        Type listType = new TypeToken<List<ChatBean.ChatItem>>(){}.getType();
        return GsonInstance.getInstance().getGson().fromJson(json, listType);
    }
}

此转换类的功能是实现对象与json数据的转换。

为了使用方便，这里将gson抽离出单例模式

所以新建GsonInstance

package com.bdtd.bdcar.common;

import com.google.gson.Gson;

public class GsonInstance {

    private static GsonInstance INSTANCE;
    private static Gson gson;

    public static GsonInstance getInstance() {
        if (INSTANCE == null) {
            synchronized (GsonInstance.class) {
                if (INSTANCE == null) {
                    INSTANCE = new GsonInstance();
                }
            }
        }
        return INSTANCE;
    }

    public Gson getGson() {
        if (gson == null) {
            synchronized (GsonInstance.class) {
                if (gson == null) {
                    gson = new Gson();
                }
            }
        }
        return gson;
    }

}

然后转换类新建完成。

在上面的实体bean，ChatBean上面添加注解。

@TypeConverters(ChatItemConverter.class)