when I try to get a EntityDao, but java.lang.NullPointerException.

[潘鑫]

public class ItemWriteServiceImpl extends BaseApplication implements ItemWriteService {

    private ItemDao itemDao;

    public ItemWriteServiceImpl() {
        this.itemDao = getDaoSession().getItemDao();
    }

    @Override
    public Boolean create(Item item) {
        try {
            itemDao.insert(item);
        }catch (Exception e) {
            e.printStackTrace();
            return Boolean.FALSE;
        }
        return Boolean.TRUE;
    }
}

And the BaseApplication as the following shows:

public class BaseApplication extends Application {

    public DaoSession daoSession;

    public DaoMaster daoMaster;

    public DaoMaster.DevOpenHelper openHelper;

    public SQLiteDatabase database;

    @Override
    public void onCreate() {
        super.onCreate();
        setDatabase();
    }

    private void setDatabase() {
        openHelper = new DaoMaster.DevOpenHelper(this, AppConstants.DB_NAME, null);
        database = openHelper.getWritableDatabase();
        daoMaster = new DaoMaster(database);
        daoSession = daoMaster.newSession();
    }

    public DaoSession getDaoSession() {
        return this.daoSession;
    }

    public SQLiteDatabase getDatabase() {
        return this.database;
    }
}

And the question is why it (ItemDao) was NullPointerException ?