首先要添加依赖

def room_version = "2.4.0"
    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"
    // optional - Test helpers
    testImplementation "androidx.room:room-testing:$room_version"
    // optional - Paging 3 Integration
    implementation "androidx.room:room-paging:2.4.0"

这里使用了viewmodel，是代码更好的封装，分类

 

 

 MainActivity,这里只控制了4个按钮

package com.example.roombasic;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;
import androidx.room.Room;
import androidx.room.Update;

import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.nio.channels.AsynchronousChannelGroup;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    Button insert, update, clear, delete;
    TextView textView;
    WordViewModel wordViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        wordViewModel = new ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory.getInstance(getApplication())).get(WordViewModel.class);
        textView = findViewById(R.id.textView);
        wordViewModel.getAllWordsLive().observe(this, new Observer<List<Word>>() {
            @Override
            public void onChanged(List<Word> words) {
                StringBuilder text = new StringBuilder();
                for (int i = 0; i < words.size(); i++) {
                    Word word = words.get(i);
                    text.append(word.getId()).append(":").append(word.getWord()).append("=").append(word.getChieseMeaning()).append("\n");
                }
                textView.setText(text.toString());
            }
        });
        insert = findViewById(R.id.insert);
        clear = findViewById(R.id.clear);
        delete = findViewById(R.id.delete);
        update = findViewById(R.id.update);
        insert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word = new Word("Hellow", "你好");
                Word word1 = new Word("World", "世界");
                wordViewModel.insertWord(word, word1);
            }
        });
        clear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                wordViewModel.deleteAllWord();
            }
        });
        update.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word = new Word("Hi", "你好啊");
                word.setId(10);
                wordViewModel.updateWord(word);
            }
        });
        delete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word = new Word("world", "世界");
                word.setId(32);
                wordViewModel.deleteWord(word);
            }
        });
    }


}

WordViewModel

package com.example.roombasic;

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<List<Word>> getAllWordsLive() {
        return wordRepository.getAllWordsLive();
    }

    void insertWord(Word... words) {
        wordRepository.insertWord(words);
    }

    void updateWord(Word... words) {
        wordRepository.updateWord(words);
    }

    void deleteWord(Word... words) {
        wordRepository.deleteWord(words);
    }

    void deleteAllWord(Void... Voids) {
        wordRepository.deleteAllWord();
    }

}

WordRepository(存储库)1.通过WordDataBase连接数据库 2.通过WordDao来进行对数据的增删改查　　

package com.example.roombasic;

import android.content.Context;
import android.os.AsyncTask;

import androidx.lifecycle.LiveData;

import java.util.List;

public class WordRepository {
    private LiveData<List<Word>> allWordsLive;
    private WordDao wordDao;

    public WordRepository(Context context) {
        WordDatabase wordDatabase = WordDatabase.getDatabase(context.getApplicationContext());
        wordDao = wordDatabase.getWordDao();
        allWordsLive = wordDao.getAllWordsLive();

    }

    public LiveData<List<Word>> getAllWordsLive() {
        return allWordsLive;
    }

    void insertWord(Word... words) {
        new InsertAsyncTask(wordDao).execute(words);
    }

    void updateWord(Word... words) {
        new UpdateAsyncTask(wordDao).execute(words);
    }

    void deleteWord(Word... words) {
        new DeleteAsyncTask(wordDao).execute(words);
    }

    void deleteAllWord(Void... voids) {
        new DeleteAllAsyncTask(wordDao).execute();
    }

    static class InsertAsyncTask extends AsyncTask<Word, Void, Void> {
        private WordDao wordDao;

        public InsertAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Word... words) {
            wordDao.insertWords(words);
            return null;
        }
    }

    static class UpdateAsyncTask extends AsyncTask<Word, Void, Void> {
        private WordDao wordDao;

        public UpdateAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Word... words) {
            wordDao.updateWords(words);
            return null;
        }
    }

    static class DeleteAsyncTask extends AsyncTask<Word, Void, Void> {
        private WordDao wordDao;

        public DeleteAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Word... words) {
            wordDao.deleteWords(words);
            return null;
        }
    }

    static class DeleteAllAsyncTask extends AsyncTask<Void, Void, Void> {
        private WordDao wordDao;

        public DeleteAllAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            wordDao.deleteAllWords();
            return null;
        }
    }
}

WordDataBase  synchronized是数据库变得单实例化

package com.example.roombasic;

import android.content.Context;

import androidx.room.Database;
import androidx.room.Insert;
import androidx.room.Room;
import androidx.room.RoomDatabase;
//singleton
@Database(entities = {Word.class}, version = 1, exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {
    private static WordDatabase INSTANCE;
    static synchronized WordDatabase getDatabase(Context context){
        if(INSTANCE==null){
            INSTANCE= Room.databaseBuilder(context.getApplicationContext(),WordDatabase.class,"word_database").build();

        }
        return INSTANCE;
    }
    public abstract WordDao getWordDao();
}

WordDao  增删改查工具类

package com.example.roombasic;

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
public interface WordDao {
    @Insert
    void insertWords(Word... words);

    @Update
    void updateWords(Word... words);

    @Delete
    void deleteWords(Word... words);

    @Query("DELETE FROM WORD")
    void deleteAllWords();

    @Query("SELECT * FROM WORD ORDER BY ID DESC")
    LiveData<List<Word>> getAllWordsLive();
}

Word  数据类

package com.example.roombasic;

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity
public class Word {
    @PrimaryKey(autoGenerate = true)
    private int id;
    @ColumnInfo(name = "english_word")
    private String word;
    @ColumnInfo(name = "chinese_word")
    private String chieseMeaning;

    public Word(String word, String chieseMeaning) {
        this.word = word;
        this.chieseMeaning = chieseMeaning;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getWord() {
        return word;
    }

    public void setWord(String word) {
        this.word = word;
    }

    public String getChieseMeaning() {
        return chieseMeaning;
    }

    public void setChieseMeaning(String chieseMeaning) {
        this.chieseMeaning = chieseMeaning;
    }
}