这篇文章是对上篇文章的优化。增加两个类,一个ViewModel管理界面数据,一个仓库类存放类。
1、Room本身支持LiveData,使用LiveData,我们就可以不用每次对页面进行刷新操作(自己写的页面刷新函数 )。我们可以用observe来观察它是否发生改变,如果改变则进行页面改变。
2、在Database改成Singleton,因为在database构造实例是非常消耗资源的,所有我们只让它构造一个实例,节省资源
3、改变线程。上一篇文章数据库的操作是在主线程,这是不对的,应该把它放到工作线程。我们可以用AsyncTask。要用AsyncTask对数据库进行操作,就需要定义多个类来继承AsyncTask这个抽象类。
实体类:
package com.example.roomtest; import androidx.room.ColumnInfo; import androidx.room.Entity; import androidx.room.PrimaryKey; @Entity // 实体类 public class Word { @PrimaryKey(autoGenerate = true) // 将id设置为主键,并且自增 private int id; @ColumnInfo(name = "English") // 设置每列的名称 private String English_word; @ColumnInfo(name = "Chinese") private String Chinese_meaning; // 主键不用构造函数 public Word(){} public Word(String english_word, String chinese_meaning) { English_word = english_word; Chinese_meaning = chinese_meaning; } public void setId(int id){ this.id = id; } public int getId() { return id; } public String getEnglish_word() { return English_word; } public void setEnglish_word(String english_word) { English_word = english_word; } public String getChinese_meaning() { return Chinese_meaning; } public void setChinese_meaning(String chinese_meaning) { Chinese_meaning = chinese_meaning; } }
Dao:
package com.example.roomtest; import androidx.lifecycle.LiveData; import androidx.room.Dao; import androidx.room.Delete; import androidx.room.Insert; import androidx.room.Query; import androidx.room.Update; import java.util.List; @Dao // 访问数据库操作的接口 Database access object public interface WordDao { //我们所有对数据库的操作都在Dao里声明 @Insert // 这些修饰词会在编译时候生成代码 void insertWords(Word... words); // 如果是一个参数就写 Word word,多个参数就这样写 @Update void updataWords(Word... words); @Delete void deleteWords(Word... words); @Query("DELETE FROM WORD") void deleteAllWords(); @Query("SELECT * FROM WORD ORDER BY ID DESC") // 获取所有的WORD,并且按照id降序排序 LiveData> getAllWordsLive(); }
Database:
package com.example.roomtest; import android.content.Context; import androidx.room.Database; import androidx.room.Room; import androidx.room.RoomDatabase; // singleton /* 这里有个参数,第一个参数entities是一个集合,因为只有一个实体类,如果有多个可以逗号隔开 第二个参数是version(版本):每一次数据库的结构发生改变,版本都得改变 第三个参数是生成数据库表:这里先选择false */ @Database(entities = {Word.class},version = 1,exportSchema = false) public abstract class WordDatabase extends RoomDatabase { private static WordDatabase INSTANCE; // 因为需要一个Context,所有我们得传来一个Context static synchronized WordDatabase getDatabase(Context context){ if(INSTANCE==null){ INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDatabase.class, "word_database") .allowMainThreadQueries().build(); } return INSTANCE; } public abstract WordDao getWordDao(); }
ViewModel:
package com.example.roomtest; import android.app.Application; import android.os.AsyncTask; import androidx.annotation.NonNull; import androidx.lifecycle.AndroidViewModel; import androidx.lifecycle.LiveData; import java.util.List; public class WordViewModel extends AndroidViewModel { private WordRepository wordRepository; public WordViewModel(@NonNull Application application) { super(application); wordRepository = new WordRepository(application); } public LiveData> getAllWordLive() { return wordRepository.getAllWordLive(); } // 定义类的接口-- 插入 public void insertWords(Word...words){ wordRepository.insertWords(words); } // 定义类的接口-- 删除 public void deleteWords(Word...words){ wordRepository.deleteWords(words); } // 定义类的接口-- 清空 public void deleteAllWords(){ wordRepository.deleteAllWords(); } // 定义类的接口-- 修改 public void updataWords(Word...words){ wordRepository.updataWords(words); } }
Repository:
package com.example.roomtest; import android.content.Context; import android.os.AsyncTask; import androidx.lifecycle.LiveData; import java.util.List; public class WordRepository { private LiveData> allWordLive; private WordDao wordDao; public WordRepository(Context context) { WordDatabase wordDatabase = WordDatabase.getDatabase(context.getApplicationContext()); wordDao = wordDatabase.getWordDao(); allWordLive = wordDao.getAllWordsLive(); } public LiveData
> getAllWordLive() { return allWordLive; } // 定义类的接口-- 插入 public void insertWords(Word...words){ new InsertAsyncTask(wordDao).execute(words); } // 定义类的接口-- 删除 public void deleteWords(Word...words){ new DeleteAsyncTask(wordDao).execute(words); } // 定义类的接口-- 清空 public void deleteAllWords(){ new DeleteAllAsyncTask(wordDao).execute(); } // 定义类的接口-- 修改 public void updataWords(Word...words){ new UpdataAsyncTask(wordDao).execute(words); } // 插入类 static class InsertAsyncTask extends AsyncTask
{ private WordDao wordDao; public InsertAsyncTask(WordDao wordDao) { this.wordDao = wordDao; } // 将在主线程的工作放到后台来执行 @Override protected Void doInBackground(Word... words) { wordDao.insertWords(words); return null; } } // 删除类 static class DeleteAsyncTask extends AsyncTask { private WordDao wordDao; public DeleteAsyncTask(WordDao wordDao) { this.wordDao = wordDao; } // 将在主线程的工作放到后台来执行 @Override protected Void doInBackground(Word... words) { wordDao.deleteWords(words); return null; } } // 清空类 static class DeleteAllAsyncTask extends AsyncTask { private WordDao wordDao; public DeleteAllAsyncTask(WordDao wordDao) { this.wordDao = wordDao; } // 将在主线程的工作放到后台来执行 @Override protected Void doInBackground(Void... voids) { wordDao.deleteAllWords(); return null; } } // 修改类 static class UpdataAsyncTask extends AsyncTask { private WordDao wordDao; public UpdataAsyncTask(WordDao wordDao) { this.wordDao = wordDao; } // 将在主线程的工作放到后台来执行 @Override protected Void doInBackground(Word... words) { wordDao.updataWords(words); return null; } } }
运行结果: