Android RxJava has joined the lists

Question

Trying to understand everything that is in RxJava. I did the following example:

private Observable<List<String>> query1() { List<String> urls = new ArrayList<>(); urls.add("1"); urls.add("2"); urls.add("3"); urls.add("4"); return Observable.just(urls); } private Observable<List<String>> query2() { List<String> urls = new ArrayList<>(); urls.add("A"); urls.add("B"); urls.add("C"); urls.add("D"); return Observable.just(urls); } 

and then tried to join two lists:

  Observable.zip( query1(), query2(), new Func2<List<String>, List<String>, Observable<String>>() { @Override public Observable<String> call(List<String> a1, List<String> a2) { List<String> list = new ArrayList<>(); list.addAll(a1); list.addAll(a2); return Observable.from(list); } }) .subscribe(new Action1<String>() { // <-- It says, cannot resolve method subscribe @Override public void call(String string) { String text = testTextView.getText().toString(); testTextView.setText(text + "\n" + string); } }); 

What am I doing wrong? I expected to see 1 2 3 4 B C D

EDIT1 I ended up with the following answer:

  Observable.zip( query1(), query2(), new Func2<List<String>, List<String>, List<String>>() { @Override public List<String> call(List<String> a1, List<String> a2) { List<String> list = new ArrayList<>(); list.addAll(a1); list.addAll(a2); return list; } }) .flatMap(new Func1<List<String>, Observable<String>>() { @Override public Observable<String> call(List<String> urls) { return Observable.from(urls); } }) .subscribe(new Action1<String>() { @Override public void call(String string) { String text = testTextView.getText().toString(); testTextView.setText(text + "\n" + string); } }); 

The EDIT2 concat solution proposed by ihuk would be much better in this case. Rate all the answers.

Answer 1

I believe that the operators you are looking for are concat or merge .

concat will emit emissions from two or more Observable without alternating them.

merge , on the other hand, will combine several observables by combining their outliers.

For instance:

  String[] numbers = {"1", "2", "3", "4"}; String[] letters = {"a", "b", "c", "d"}; Observable<String> query1 = Observable.from(numbers).delay(1, TimeUnit.SECONDS); Observable<String> query2 = Observable.from(letters); Observable .concat(query1, query2) .subscribe(s -> { System.out.printf("-%s-" + s); }); 

-1--2--3--4--a--b--c--d- will be printed. If you replace concat with merge , the result will be -a--b--c--d--1--2--3--4- .

Operator

Zip combines several Observable together using the specified function. for instance

  Observable .zip(query1, query2, (String n, String l) -> String.format("(%s, %s)", n, l)) .subscribe(s -> { System.out.printf("-%s-", s); }); 

Output -(1, a)--(2, b)--(3, c)--(4, d)- .

Answer 2

thats because you are trying to return an Observable from a zip function, but then you go through an Action<String>

 Observable.zip( query1(), query2(), new Func2<List<String>, List<String>, List<String>>() { @Override public List<String> call(List<String> a1, List<String> a2) { List<String> list = new ArrayList<>(); list.addAll(a1); list.addAll(a2); return list; } }) .subscribe( (string)-> System.out.println(string) ); 

Answer 3

  Observable<List<String>> query1(){ List<String> s = new ArrayList<>(); s.add("1");s.add("1");s.add("1"); return Observable.just(s); } Observable<List<String>> query2(){ List<String> s = new ArrayList<>(); s.add("1");s.add("1");s.add("1"); return Observable.just(s); } void HelloRx(){ Map<String,String> map2=new LinkedHashMap<>();//pick the result you want to return Here ! Observable.zip(query1(),//Observable Method 1 query2(),//Observable Method 2 (result1,result2)->{ for(String s : result1){//result1 is the value returned by query1 , result2 ...u know. //do whatever you want //map.put(......) } return null; }) .subscribeOn(BackgroundSchedulers.getMultiThreadInstance()) .observeOn(AndroidSchedulers.mainThread()) .doOnCompleted(() -> { //Do Something when finish for example transmit data to your adapter }) .subscribe(); } 

Answer 4

Obviously, to combine two lists into one list, you can make Observable.concat() on your Observable.from() , and then call Observable.toList() .

 RealmResults<Cat> equalTo; RealmResults<Cat> beginsWith; @Override public void onViewRestored() { compositeSubscription = new CompositeSubscription(); equalTo = realm.where(Cat.class).equalTo("field", filterString).findAllSorted("field"); beginsWith = realm.where(Cat.class).beginsWith("field", filterString).findAllSorted("field"); compositeSubscription.add(realm.asObservable() .switchMap(new Func1<Realm, Observable<Cat>>() { @Override public Observable<Cat> call(Realm realm) { return Observable.concat(Observable.from(equalTo), Observable.from(beginsWith)); } }) .toList() .subscribe(cats -> { // update adapter with List<Cat> }));