使用 Retrofit 请求响应刷新 livedata

Question

我有一个简单的应用程序，它显示电影列表。当用户单击一个按钮时，它应该刷新列表，这意味着再次进入 Retrofit 并获取新列表。 问题是，这种刷新不起作用。当我打开应用程序时，它只会获取一次列表。

public class MoviesViewModel extends AndroidViewModel {
    private MutableLiveData<Resource<List<Movie>>> mLastdMovieListObservable;
    private Repository mRepository;

    public MoviesViewModel(Application application) {
        super(application);
        mRepository = new Repository();
    }

    public LiveData<Resource<List<Movie>>> getMovieListLiveData() {
        if (mLastdMovieListObservable == null) {
            mLastdMovieListObservable = mRepository.getMovieList();
        }
        return mLastdMovieListObservable;
    }
}

和存储库：

public MutableLiveData<Resource<List<Movie>>> getMovieList() {
    final MutableLiveData<Resource<List<Movie>>> data = new MutableLiveData<>();
    data.setValue(Resource.loading(null));

    mInterface.getMovies(.....).enqueue(new Callback<MovieListResponse>() {
        @Override
        public void onResponse(Call<MovieListResponse> call, Response<MovieListResponse> response) {
            if (response.isSuccessful()) {
                data.postValue(Resource.success(response.body().getResult()));
            } else {
                data.postValue(Resource.error(response.message(), null));
            }
        }
        @Override
        public void onFailure(Call<MovieListResponse> call, Throwable t) {
            data.postValue(Resource.error(t.getMessage(), null));
        }
    });

    return data;
}   

然后在片段中它只是：

mMoviesViewModel.getMovieListLiveData().observe(this, moviesResource -> {
    if (moviesResource.status == Status.SUCCESS) {
       .....
       .....

然后是按钮点击部分，当我需要再次获取列表时，我不确定如何实现它。 我尝试过的任何东西都不起作用。存储库立即将数据返回为空。

Answer 1

您可以使用重试方法，我快速更改了您的代码作为重试示例，并检查此源以获得更好的代码。LINK

Transformations.switchMap 监听重试，当它改变时，将再次调用 swithMap。在 UI ViewModel 中应该像下面这样配置，但在按钮中你只需要调用重试。

mMoviesViewModel.getMovieListLiveData().observe(this, moviesResource -> {
if (moviesResource.status == Status.SUCCESS) {
   .....
   .....

在按钮中：

mMoviesViewModel.retry()

还有 ViewModel：

public class MoviesViewModel extends AndroidViewModel {
private MutableLiveData<Resource<List<Movie>>> mLastdMovieListObservable;
private Repository mRepository;
private Boolean mRetry = false;

public MoviesViewModel(Application application) {
    super(application);
    mRepository = new Repository();
    mLastdMovieListObservable = Transformations.switchMap(mRetry){
        mLastdMovieListObservable = mRepository.getMovieList()
    }
}

public LiveData<Resource<List<Movie>>> getMovieListLiveData() {
    return mLastdMovieListObservable;
}

public void retry(){
    mRetry.setValue(true)
}}

Answer 2

电影类型的变化如下：

public class MoviesViewModel extends AndroidViewModel {
private MutableLiveData<Resource<List<Movie>>> mLastdMovieListObservable;
private Repository mRepository;
private Int mMovieType = 0;

public MoviesViewModel(Application application) {
    super(application);
    mRepository = new Repository();
    mLastdMovieListObservable = Transformations.switchMap(mMovieType, type->
        mLastdMovieListObservable = mRepository.getMovieList(type)
    );
}

public LiveData<Resource<List<Movie>>> getMovieListLiveData() {
    return mLastdMovieListObservable;
}

public void setMovieType(Int movieType){
    mMovieType.setValue(movieType)
}

}