Room (二) 进阶和完善

1. Word 类不做修改

@Entity
public class Word {
    @PrimaryKey(autoGenerate = true)
    private int id; //主键
    @ColumnInfo(name = "english_word")
    private String word;
    @ColumnInfo(name = "chinese_meaning")
    private String chineseMeaning;

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

    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 getChineseMeaning() {
        return chineseMeaning;
    }

    public void setChineseMeaning(String chineseMeaning) {
        this.chineseMeaning = chineseMeaning;
    }
}

2. 修改 WordDao

@Dao //Database access object
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();
    //List<Word> getAllWords();
}

3. 修改 WordDatabase，只允许生成一个实例

//singleton 只允许生成一个实例
@Database(entities = {Word.class}, version = 1, exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {
    private static WordDatabase INSTANCE;

    //synchronized: 解决多个线程下调用，创建多个实例问题
    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();
}

4. 创建 Repository:仓库 获取数据的意思, 代码进行归类

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

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

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

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

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

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

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

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

        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;

        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;

        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;

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

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

5. 创建 ViewModel

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

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

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

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

6. 调用测试

public class MainActivity extends AppCompatActivity {
    TextView textView;
    Button btInsert, btUpdate, btDelete, btClear;
    WordViewModel viewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = findViewById(R.id.textView);
        viewModel = new ViewModelProvider(this).get(WordViewModel.class);
        viewModel.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");
                }
                textView.setText(text.toString());
            }
        });

        View.OnClickListener listener = new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                switch (view.getId()) {
                    case R.id.bt_insert:
                        Word word1 = new Word("Hello", "你好!");
                        Word word2 = new Word("World", "世界!");
                        viewModel.insertWords(word1, word2);
                        break;
                    case R.id.bt_clear:
                        viewModel.deleteAllWords();
                        break;
                    case R.id.bt_update:
                        Word word = new Word("Hi", "嗨");
                        word.setId(51);
                        viewModel.updateWords(word);
                        break;
                    case R.id.bt_delete:
                        Word word_d = new Word("一", "1");
                        word_d.setId(52);
                        viewModel.deleteWords(word_d);
                        break;
                }
            }
        };
        btInsert = findViewById(R.id.bt_insert);
        btClear = findViewById(R.id.bt_clear);
        btUpdate = findViewById(R.id.bt_update);
        btDelete = findViewById(R.id.bt_delete);
        btDelete.setOnClickListener(listener);
        btInsert.setOnClickListener(listener);
        btClear.setOnClickListener(listener);
        btUpdate.setOnClickListener(listener);
    }
}