Pagination With RxJava In Android

Posted By : Rahul Baboria | 30-Apr-2018

android

Introduction:

RxJava is based on live data, pagination is also kind of live data scheme where when a user scrolls it loads more and more data.

Paging Library Components

The principal segment of a paging library are DataSource, PagedList, and PagedListAdapter

DataSource

This a segment in charge of stacking the information. Contingent upon how you have to get to your information, you would expand one of its subclasses. At our utilization case, we stack the following page by knowing the last component id in the wake of perusing the docs sound helpful to utilize ItemKeyedDataSource for more points of interest and different subclass check the docs.

PagedList

This an A wrapper list that holds your information and advises the information source when to stack information. You can design how much information is stacked at once, and how much information ought to be prefetched. It gives updates to the connector as the information stacked in pages

PagedListAdapter

This class is the usage of RecyclerView.adapter that presents information from PagedList and take DiffUtil as a parameter to figure the distinction in the information and do all the refreshing work for you.

How about we consider we have REST API here when the information originates from DataSource on a foundation string. It will refresh the PagedList value, The PagedList informs its eyewitnesses of the new rundown on the mainThread. Presently the PagedListAdapter will get the new rundown. On the foundation, string will register the progressions utilizing Diffutils and back with the outcome on the mainThread at that point call onBindViewHolder with refreshed information to refresh the view

Add following dependencies in build.gradle

//Networking retrofit implementation

com.squareup.retrofit2:retrofit:2.3.0

implementation com.squareup.retrofit2:converter-gson:2.3.0

implementation com.squareup.retrofit2:adapter-rxjava2:2.3.0
//RxJava implementation

io.reactivex.rxjava2:rxjava:2.1.9

implementation io.reactivex.rxjava2:rxandroid:2.0.2

  Disposable disposable = paginator
                .onBackpressureDrop()
                .subscribeOn(Schedulers.io())
                .concatMap(new Function<Integer, Publisher<List<Model>>>() {
                    @Override
                    public Publisher<List<Model>> apply(@NonNull Integer page) throws Exception {
                       loading = true;
                        // show progressbar
                        return networkService.getDataFromApi(accessToken,new AppContext(mContext).getKeyApiSession(), page+"")
                                .subscribeOn(Schedulers.newThread())
                                .doOnError(new Consumer<Throwable>() {
                                    @Override
                                    public void accept(Throwable throwable) throws Exception {
                                       // handle exceptions here
                                    }
                                });
                    }
                })
              
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer<List<Model>>() {
                    @Override
                    public void accept(@NonNull List<Hotel> items) throws Exception {
                        //paginationAdapter.addItems(items);
                        //paginationAdapter.notifyDataSetChanged();
                        loading = false;
                        // hide loadmore

                    }

                });

finally add disposable to composite disposables list.

 compositeDisposable.add(disposable);
        paginator.onNext(pageNumber);

We need addOnScrollLister to the recycled view when user scrolls it triggers according to a threshold. Let's take an example, if VISIBLE_THRESHHOLD = 50, infinite scroll API will be called if listing contains less than 50 items from the current position.

 private void setUpLoadMoreListener() {
        recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView,
                                   int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                totalItemCount = layoutManager.getItemCount();
                lastVisibleItem = layoutManager
                        .findLastVisibleItemPosition();
                if (!loading
                        && totalItemCount <= (lastVisibleItem + VISIBLE_THRESHOLD)) {
                    pageNumber++;
                    paginator.onNext(pageNumber);
                    loading = true;
                }
            }
        });
    }