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

場景

在Android中使用Room進行存儲數據庫時提示:

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

 

 

 

 

 

注：

博客：
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實現

這是因為Room中不支持對象中直接存儲集合。

下面是要存儲的對象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;
        //語音消息服務器地址
        private String remoteContent;
        private String sender;
        private String receiver;
        private String type;
        private boolean canReceived;
        private String sendTime;
        private String receivedTime;
        //語音時長
        private int voiceDuration;
        private boolean isRead;

    }

}

 

上面省略了get和set方法，在bean中還有個 對象集合data,對象為ChatItem

所以需要新建一個轉換類ChatItemConverter

名字根據自己業務去定

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);
    }
}

 

此轉換類的功能是實現對象與json數據的轉換。

為了使用方便，這里將gson抽離出單例模式

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;
    }

}

 

然后轉換類新建完成。

在上面的實體bean，ChatBean上面添加注解。

@TypeConverters(ChatItemConverter.class)