实时数据未更新 ViewModel

Question

我正在 Activity:

中观察我的视图模型

private void setupViewModel() {
    SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
    mSortCategory = sharedPreferences.getString(getString(R.string.pref_sort_key), getString(R.string.pref_sort_popular));
    MainViewModelFactory factory = new MainViewModelFactory(mSortCategory);
    mViewModel = ViewModelProviders.of(this, factory).get(MainViewModel.class);
    mViewModel.getResponse().observe(this, new Observer<MovieResponse>() {
        @Override
        public void onChanged(MovieResponse movieResponse) {
            mMovieAdapter.setData(movieResponse.getResults());
            mCurrentPage = movieResponse.getPage();
            mTotalPages = movieResponse.getTotalPages();
            Log.d(TAG, "setupviewmodel: " + movieResponse.getResults().get(0).getOriginalTitle());
        }
    });

这是我的虚拟机：

public class MainViewModel extends ViewModel {
private MutableLiveData<MovieResponse> mMoviesResponseLiveData;

public MainViewModel(String category) {
    mMoviesResponseLiveData = Repository.getInstance().loadMoviesFromApi(category, 1);
}

public void loadMovies(String category, int currentPage) {
    mMoviesResponseLiveData = Repository.getInstance().loadMoviesFromApi(category, currentPage);
}

public MutableLiveData<MovieResponse> getResponse() {
    return mMoviesResponseLiveData;
}

然后我打电话给 retrofit:

 public MutableLiveData<MovieResponse> loadMoviesFromApi(String sort, int page) {
    final MutableLiveData<MovieResponse> data = new MutableLiveData<>();
    Call<MovieResponse> call = mApiService.getMoviesResponse(sort, BuildConfig.OPEN_WEATHER_MAP_API_KEY, page);
    Log.d(TAG, "loadMoviesFromApi: " + call.request().url().toString());
    call.enqueue(new Callback<MovieResponse>() {
        @Override
        public void onResponse(Call<MovieResponse> call, Response<MovieResponse> response) {
            if (response.isSuccessful()) {
                data.setValue(response.body());
            }
        }
        @Override
        public void onFailure(Call<MovieResponse> call, Throwable t) {
            t.printStackTrace();
        }
    });
    return data;
}

据我所知，新数据应该通过在 Viewmodel 上调用 activity 的方法来异步加载：

private void updateUI() {
    mViewModel.loadMovies(mSortCategory, mCurrentPage);
}

我从 retrofit 接收数据。但出于某种原因，未观察到实时数据。

Answer 1

由于此方法，您的观察者未收到通知：

public void loadMovies(String category, int currentPage) {
    mMoviesResponseLiveData = Repository.getInstance().loadMoviesFromApi(category, currentPage);
}

loadMoviesFromApi return 是 LiveData 的新实例，因此您的 viewModel 不再引用从 getResponse 编辑的 LiveData return。如果你想让你的观察者得到通知，你应该 return 来自方法 loadMovies 的 ViewModel 并观察它或调用 mMoviesResponseLiveData.postValue(responseFromRetrofit)

实时数据未更新 ViewModel

Live Data is not updating ViewModel

android

android-lifecycle

retrofit

android-livedata