Dealing with multiple sources brings in a new possible scenario: receiving data from multiple Observables, processing them, and making them available as a new Observable sequence. RxJava has a specific method to accomplish this: zip() combines the value emitted by two or more Observables, transforms them according to a specified function Func*, and emits a new value. The following figure shows how the zip() method processes the emitted "numbers" and "letters" and makes them available as a new item:
For our real-world example, we are going to use our installed apps list and a new dynamic Observable to make the example a bit spicy:
Observable<Long> tictoc = Observable.interval(1, TimeUnit.SECONDS);
The tictoc Observable variable uses the interval() function to generate a Long item every second: simple but effective. As stated previously, we are going to need a Func object. It will be Func2 because we are going to pass two parameters to it:
private AppInfo updateTitle(AppInfoappInfo, Long time) {
appInfo.setName(time + " " + appInfo.getName());
return appInfo;
}Now, our loadList() function will look like this:
private void loadList(List<AppInfo> apps) {
mRecyclerView.setVisibility(View.VISIBLE);
Observable<AppInfo> observableApp = Observable.from(apps);
Observable<Long> tictoc = Observable.interval(1, TimeUnit.SECONDS);
Observable
.zip(observableApp, tictoc, (AppInfoappInfo, Long time) ->updateTitle(appInfo, time))
.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);
}
});
}As you can see, zip() has three parameters: the two Observables and Func2, as expected.
A closer look will reveal the observeOn() function. It will be explained in the next chapter: let's say it is a leap of faith for now.
As a result, we have:
