RxJava's combineLatest() acts like a particular type of zip(). As we already learned, zip() works on the latest unzipped item of the two Observables. Instead, combineLatest() works on the latest emitted items: if Observable1 emits A and Observable2 emits B and C, combineLatest() will process AB and AC pairs, as shown in the following figure:
The combineLatest() function takes up to nine Observables as parameters, or even a list of Observables, if needed.
Borrowing the loadList() function from the previous example, we can modify it to achieve a real-world example for combineLatest():
private void loadList(List<AppInfo> apps) {
mRecyclerView.setVisibility(View.VISIBLE);
Observable<AppInfo> appsSequence = Observable.interval(1000, TimeUnit.MILLISECONDS)
.map(position ->apps.get(position.intValue()));
Observable<Long> tictoc = Observable.interval(1500, TimeUnit.MILLISECONDS);
Observable
.combineLatest(appsSequence, tictoc, this::updateTitle)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Observer<AppInfo>() {
@Override
public void onCompleted() {
Toast.makeText(getActivity(), "Here is the list!", Toast.LENGTH_LONG).show();
}
@Override
public void onError(Throwable e) {
mSwipeRefreshLayout.setRefreshing(false);
Toast.makeText(getActivity(), "Something went wrong!", Toast.LENGTH_SHORT).show();
}
@Override
public void onNext(AppInfoappInfo) {
if (mSwipeRefreshLayout.isRefreshing()) {
mSwipeRefreshLayout.setRefreshing(false);
}
mAddedApps.add(appInfo);
intposition = mAddedApps.size() - 1;
mAdapter.addApplication(position, appInfo);
mRecyclerView.smoothScrollToPosition(position);
}
});
}We are using two Observables here: one emits an app from our installed apps list every second, and the second one emits a Long item every 1.5 seconds. We combine them and apply the updateTitle() function. As result, we obtain:
As you can see, due to the different time intervals, the AppInfo object sometimes repeats, as expected.