I've implemented the app using a MVVM'ish approach. Since it is a simple app I may have broken some "rules".
On the Model/Data Layer I've used Retrofit for the API calls. These calls returns a Response DTO and are accessed via GiphyRepository Repository. The Repository calls returns a LiveData of DataState<T>that represents 3 different states of the Call, loading, data (data available) and error
The ViewModel exposes a UiState LiveData. UiState has 4 distinct states: LOADING, LOADED (with a List<GiphyUiModel>), ERROR and COMPLETED (no more items available)
The ViewModel also have an internal Query LiveData. A Query can represent the TRENDING and SEARCH feeds. The View calls setQuery(query) to request data from the ViewModel. Once a new query value is set, the Transformations.switchMap() will run with the new value and will call the appropriate Repository call
private final MutableLiveData<Query> query = new MutableLiveData<>(Query.trending());
private final LiveData<UiState<List<GiphyUiModel>>> uiState = createUiStateLiveData();
private LiveData<UiState<List<GiphyUiModel>>> createUiStateLiveData() {
return Transformations.switchMap(query, query -> {
// Call the repository based on the current query.
}
}
public LiveData<UiState<List<GiphyUiModel>>> getUiState() {
return uiState;
}
The View layer simply observes the ViewModel UiState ** LiveData** (viewModel.getUiState().observe())
The RecyclerView has an EndlessScrollListener that calls setQuery on the ViewModel, so it can download more data.
@Override
public void onLoadMore() {
Query currentQuery = viewModel.getQuery();
viewModel.setQuery(currentQuery);
}
Also the SearchView also calls on the ViewModel's setQuery after debouncing the value for 500ms.
private final Debouncer<String> debouncer = new Debouncer<>("", value -> {
viewModel.setQuery(Query.search(value));
});
I also added some sugar to the MainActivity, like implementing Glide's RecyclerViewPreloader and hiding the keyboard on scroll when searching...
If this was a bigger/serious app, I'd probably have used a Interactor/UseCase between the ViewModel and the Repository. And if I could, let's say I was implementing a new feature on an existing code base, I'd try to implement the Interactor/UseCase and the Repository and Kotlin, where I could use Coroutines to simplify and avoid callbacks, and just return a LiveData to the old Java code.