I'm using Paging library to paginate a list of items I'm retrieving from my server. Initially, when my fragment is loaded, it returns an empty list. But after changing fragments and going back to that fragment, I can see the list loaded. After debugging I saw that data was actually being fetched, but an empty list was passed to my fragment.
ItemDataSource:
@Override
public void loadInitial(@NonNull LoadInitialParams<Integer> params, @NonNull LoadInitialCallback<Integer, Item> callback) {
apiService.getItems(OFFSET)
.enqueue(new Callback<ItemWrapper>() {
@Override
public void onResponse(@NonNull Call<ItemWrapper> call,@NonNull Response<ItemWrapper> response) {
callback.onResult(response.body().getItems(), null, OFFSET + 25);
}
@Override
public void onFailure(@NonNull Call<ItemWrapper> call,@NonNull Throwable t) {
t.printStackTrace();
}
});
}
@Override
public void loadBefore(@NonNull LoadParams<Integer> params, @NonNull LoadCallback<Integer, Item> callback) {
}
@Override
public void loadAfter(@NonNull LoadParams<Integer> params, @NonNull LoadCallback<Integer, Item> callback) {
apiService.getItems(params.key)
.enqueue(new Callback<ItemWrapper>() {
@Override
public void onResponse(@NonNull Call<ItemWrapper> call,@NonNull Response<ItemWrapper> response) {
Integer key = response.body().getItems().isEmpty() ? null : params.key + 25;
callback.onResult(response.body().getItems(), key);
}
@Override
public void onFailure(@NonNull Call<ItemWrapper> call,@NonNull Throwable t) {
t.printStackTrace();
}
});
}
ItemDataSourceFactory:
@Override
public DataSource create() {
ItemDataSource itemDataSource = new ItemDataSource();
itemLiveDataSource.postValue(itemDataSource);
return itemDataSource;
}
public MutableLiveData<ItemDataSource> getItemLiveDataSource() {
return itemLiveDataSource;
}
ItemViewModel:
private LiveData<ItemDataSource> liveDataSource;
private LiveData<PagedList<Item>> itemPagedList;
private ItemViewModel(Application application) {
ItemDataSourceFactory factory = new ItemDataSourceFactory();
liveDataSource = factory.getItemLiveDataSource();
PagedList.Config config = (new PagedList.Config.Builder())
.setEnablePlaceholders(false)
.setPageSize(ItemDataSource.LIMIT).build();
itemPagedList = (new LivePagedListBuilder(factory, config)).build();
}
public LiveData<PagedList<Item>> getItems() {
return itemPagedList;
}
Fragment:
ItemViewModel itemViewModel = ViewModelProviders.of(this).get(ItemViewModel.class);
itemViewModel.getItems.observe(this, items -> {
adapter.submitList(items);
})
Not 100% sure, but I think this is because you are running an asynchronous request. try to change it to run synchronously for loadInitial()
like so request.execute()
I also had this problem once and I still can't figure it out why it does not work for some fragments. The solution I found, aldo being more like a fast sketchy fix is to load the fragment twice.
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