Android Studio Room中带参数的java查询

Question

我想问一个问题，让所有的鸟都在一个家庭，我不知道如何做到这一点。到目前为止，我已经做到了这一点，但我觉得我遗漏了一些东西：

道：

@Query("Select * from bird WHERE family=:family")
public LiveData<List<Bird>> getBirdsFromFamily(String family);

存储库：

private LiveData<List<Bird>> allBirdsFromFamily;

private String family;

public BirdRepository(Application application){
    Database database = Database.getInstance(application);
    dao = database.dao();


    allBirdsFromFamily = dao.getBirdsFromFamily(family);
}


public LiveData<List<Bird>> getBirdsFromFamily(String family){
    return allBirdsFromFamily; 
}

视图模型：

private LiveData<List<Bird>> allBirdsFromFamily;

private String family;


public BirdViewModel(@NonNull Application application) {
    super(application);
    birdRepository = new BirdRepository(application);

    allBirdsFromFamily = birdRepository.getBirdsFromFamily(family);

}


public LiveData<List<Bird>> getAllBirdsFromFamily(String family)
{
    return allBirdsFromFamily;
}

我有一份家庭名单和一份鸟类名单

当点击家族列表中的一个项目时，我想打开一个包含所有鸟类的列表。我可以从该项中获取字符串，但调用该方法时不会显示任何内容

    String family = intent.getStringExtra(AddEditFamilyActivity.EXTRA_FAMILY);

        birdViewModel.getAllBirdsFromFamily(family).observe(this, new Observer<List<Bird>>() {

            @Override
            public void onChanged(@Nullable List<Bird> birds) { //everytime something changes, the adaptater is updated
                //update the recycler view
                adapter.submitList(birds);
            }

        });

Answer 1

由于我的评论有点长，我将发表一篇文章

I don't have any doInBackGround for this query, how should I do it ?

是的，当您查询数据库时，出于两个原因希望避免使用主线程，第一个原因是因为Android会让您崩溃，告诉您不要这样做。第二种方法是让用户在获取数据的同时与应用程序交互

在本doc中，您可以查看示例和代码实验室，并学习如何正确调用数据库

Answer 2

我用一个工厂解决了这个问题-没有必要使用doInBackground，因为它只是一个“get”查询：

道：

@Query("Select * from bird WHERE family=:family ORDER BY name")
public LiveData<List<Bird>> getBirdsFromFamily(String family);

存储库：

private LiveData<List<Bird>> allBirdsFromFamily;
private String family;

public BirdRepository(Application application){
    Database database = Database.getInstance(application);
    birdDao = database.dao();

    allBirdsFromFamily = birdDao.getBirdsFromFamily(family);
}


public LiveData<List<Bird>> getAllBirdsFromFamily(String family){
    return birdDao.getBirdsFromFamily(family);
}

视图模型：

       private LiveData<List<Bird>> allBirdsFromFamily;
          private BirdRepository repository;

            public BirdViewModel(@NonNull Application application, String family ) {
                super(application);
                this.application = application;

                repository = new BirdRepository(application);
    allBirdsFromFamily = repository.getAllBirdsFromFamily(family);
            }    

        public LiveData<List<Bird>> getAllBirdsFromFamily(String family) { return repository.getAllBirdsFromFamily(family); }

ViewModelFactory：

    private Application mApplication;
    private String mfamily;

    public BirdViewModelFactory(@NonNull Application application, String family) {
        mApplication = application;
        mfamily = family;
    }

    @NonNull
    @Override
    public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
        return (T) new BirdViewModel(mApplication, mfamily);
    }

活动：

     BirdViewModelFactory factory = new BirdViewModelFactory(this.getApplication(), family);
     birdViewModel = new ViewModelProvider(this, factory).get(BirdViewModel.class);