检索会议室数据库中单行的数据

Question

我是android studio的新手，我才刚刚开始学习它。我学会了从房间数据库中获取数据并将其粘贴到Recyclerview中。现在我只想从会议室数据库中获取一行数据。在此行中，有ID，用户名和user_telephone_number。所以我创建了UserEntity，UserDao，Database，UserRepository，UserViewModel，但我陷入了困境。当我在前面提到的所有人员之后使用Recyclerview进行相同操作时，我都创建了RecyclerView.Adapter，在这种情况下，我不确定我是否需要Adapter还是有其他方法？ ，下面是我到目前为止所做的代码。

道

@Dao
public interface UserDao {

    @Insert
    void insert(UserEntity userEntity);

    @Update
    void update(UserEntity userEntity);

    @Delete
    void delete(UserEntity userEntity);

    @Query("DELETE FROM user_table")
    void deleteAllUsers();

    @Query("SELECT * FROM user_table")
    LiveData<List<UserEntity>> getAllUsers();

}

实体

@Entity(tableName = "user_table")
public class UserEntity {

    @PrimaryKey(autoGenerate = true)
    private int id;

    private String user_name;

    private String user_telephone_number;

    public UserEntity(String user_name, String user_telephone_number) {
        this.user_name = user_name;
        this.user_telephone_number = user_telephone_number;
    }

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

    public int getId() {
        return id;
    }

    public String getUser_name() {
        return user_name;
    }

    public String getUser_telephone_number() {
        return user_telephone_number;
    }
}

存储库（我知道AsyncTask已过时，它将是下一课/问题）

public class UserRepository {
    private UserDao userDao;
    private LiveData<List<UserEntity>> allUsers;

    public UserRepository(Application application) {
        HandymanDatabase handymanDatabase = HandymanDatabase.getInstance(application);
        userDao = handymanDatabase.userDao();
        allUsers = userDao.getAllUsers();
    }

    public void insert(UserEntity userEntity) {
        new InsertUserAsyncTask(userDao).execute(userEntity);
    }

    public void update(UserEntity userEntity) {
        new UpdateUserAsyncTask(userDao).execute(userEntity);
    }

    public void delete(UserEntity userEntity) {
        new DeleteUserAsyncTask(userDao).execute(userEntity);
    }

    public void deleteAllUsers() {
        new DeleteAllUsersAsyncTask(userDao).execute();
    }

    public LiveData<List<UserEntity>> getAllUsers() {
        return allUsers;
    }

    private static class InsertUserAsyncTask extends AsyncTask<UserEntity, Void, Void> {
        private UserDao userDao;

        private InsertUserAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(UserEntity... userEntities) {
            userDao.insert(userEntities[0]);
            return null;
        }
    }

    private static class UpdateUserAsyncTask extends AsyncTask<UserEntity, Void, Void> {
        private UserDao userDao;

        private UpdateUserAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(UserEntity... userEntities) {
            userDao.update(userEntities[0]);
            return null;
        }
    }

    private static class DeleteUserAsyncTask extends AsyncTask<UserEntity, Void, Void> {
        private UserDao userDao;

        private DeleteUserAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(UserEntity... userEntities) {
            userDao.delete(userEntities[0]);
            return null;
        }
    }

    private static class DeleteAllUsersAsyncTask extends AsyncTask<Void, Void, Void> {
        private UserDao userDao;

        private DeleteAllUsersAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            userDao.deleteAllUsers();
            return null;
        }
    }
}

ViewModel

public class UserViewModel extends AndroidViewModel {
    private UserRepository userRepository;
    public LiveData<List<UserEntity>> allUsers;

    public UserViewModel(@NonNull Application application) {
        super(application);
        userRepository = new UserRepository(application);
        allUsers = userRepository.getAllUsers();
    }

    public void insert(UserEntity userEntity) {
        userRepository.insert(userEntity);
    }

    public void update(UserEntity userEntity) {
        userRepository.update(userEntity);
    }

    public void delete(UserEntity userEntity) {
        userRepository.delete(userEntity);
    }

    public void deleteAllUsers() {
        userRepository.deleteAllUsers();
    }

    public LiveData<List<UserEntity>> getAllUsers() {
        return allUsers;
    }
}

片段

public class UserFragment extends Fragment {

    private UserViewModel userViewModel;

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

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view = getLayoutInflater().inflate(R.layout.fragment_user, container, false);

        final TextView textViewUserName = view.findViewById(R.id.textViewUserName);
        TextView textViewUserPhone = view.findViewById(R.id.textViewUserPhone);

        userViewModel = new ViewModelProvider(this).get(UserViewModel.class);
        userViewModel.getAllUsers().observe(getViewLifecycleOwner(), new Observer<List<UserEntity>>() {
            @Override
            public void onChanged(List<UserEntity> userEntities) {

                **---> Here I'm stuck <---**

            }
        });

        return view;
    }
}

非常感谢您提供的帮助。