Android 使用Room操作SQLite数据库让其变得无比高效和简洁(前一篇文章的完善)

Posted 2021-12-02 路宇

上一篇文章地址：Android 使用Room操作SQLite数据库让其变得无比高效和简洁(教程一)
下一篇文章地址：

Android使用Room操作SQLite数据库让其变得无比高效和简洁(进一步完善用RecyclerView显示数据库中的数据)

Android 使用Room操作数据库进行数据库版本的升级和迁移

这篇文章我们将上一个demo进行了四个方面的完善，

1. 引入了LiveData
2. 引入了AsyncTask后台执行
3. 将WordDataBase这个类，修改为了单例模式
4. 引入了ViewModel，使用ViewModel来管理界面的数据，使得MainActivity中的代码得到了精简，只管理界面的操作，跟操作数据没有直接的关联。

布局页面还是一样的不再给出代码

首先修改了WordDao这里面的代码，引入了LiveData

//访问数据库操作的接口
@Dao
public interface WordDao {
    //添加数据
    @Insert
    void insertWords(Word...words);
    @Delete
    void deleteWords(Word...words);
    @Query("DELETE FROM WORD")
    void deleteAllWords();
    @Update
    void updateWords(Word...words);
    @Query("SELECT * FROM WORD ORDER BY ID DESC")
//    List<Word> getAllWords();
    LiveData<List<Word>> getAllWordsLive();
}

之后将WordDataBase改为了单例模式，代码如下：

// 参数1：实体类  参数2：数据库版本号 参数3：禁止将数据库架构导入到给定的文件夹中
@Database(entities = {Word.class},version = 1,exportSchema = false)
public abstract class WordDataBase extends RoomDatabase {
    private static WordDataBase INSTANCE;
    public 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();
}

之后创建WordViewModel类，在创建WordViewModel类之前，应该创建一个仓库类WordRepository，来作为中介，通过这个仓库类来获取和存储数据
WordRepository类如下：

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

    public WordRepository(Context context) {
        WordDataBase wordDataBase = WordDataBase.getDatabase(context);
        wordDao = wordDataBase.getWordDao();
        allWordsLive = wordDao.getAllWordsLive();
    }

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

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

    public void deleteAllWords() {
        new DeleteAllAsyncTask(wordDao).execute();
    }

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

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

    private 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;
        }

    }

    private 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;
        }

    }

    private 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;
        }

    }

    private 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;
        }
    }
}

之后创建WordViewModel类管理数据：

public class WordViewModel extends androidViewModel {
    private WordDao wordDao;
    private WordRepository wordRepository;

    public WordViewModel(@NonNull Application application) {
        super(application);
        wordRepository = new WordRepository(application);
    }

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

    public void insertWords(Word... words) {
        wordRepository.insertWords(words);
    }

    public void updateWords(Word... words) {
        wordRepository.updateWords(words);
    }

    public void deleteAllWords() {
        wordRepository.deleteAllWords();
    }

    public void deleteWords(Word... words) {
        wordRepository.deleteWords(words);
    }

}

最后自然是MainActivity中的代码，这次里面的代码就非常的精简了：

public class MainActivity extends AppCompatActivity {
    private Button btn_insert, btn_clear, btn_update, btn_delete;
    private TextView tv_text;
    private WordViewModel wordViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
//        wordDataBase = Room.databaseBuilder(this, WordDataBase.class, "word_database")
//                .build();
        btn_insert = findViewById(R.id.btn_insert);
        btn_clear = findViewById(R.id.btn_clear);
        btn_update = findViewById(R.id.btn_update);
        btn_delete = findViewById(R.id.btn_delete);
        tv_text = findViewById(R.id.tv_text);
//        wordViewModel =new WordViewModel(getApplication());
        wordViewModel = ViewModelProviders.of(this).get(WordViewModel.class);

        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.getChineseMeaning()).append("\\n");
                }
                tv_text.setText(text.toString());
            }
        });
        btn_insert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Word word1 = new Word("Hello", "你好！");
                Word word2 = new Word("World", "世界！");
//                wordDao.insertWords(word1, word2);
                wordViewModel.insertWords(word1, word2);
            }
        });
        btn_clear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
//                wordDao.deleteAllWords();
                wordViewModel.deleteAllWords();
            }
        });
        btn_update.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word = new Word("Hi", "你好啊");
                word.setId(120);
//                wordDao.updateWords(word);
                wordViewModel.updateWords(word);
            }
        });
        btn_delete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word = new Word("Hi", "你好啊");
                word.setId(120);
//                wordDao.deleteWords(word);
                wordViewModel.deleteWords(word);
            }
        });
    }
}

后续会持续更新Room操作数据库的相关内容~ 有不当之处 也可以在评论区留言指出！