Create list with objects from another list using RxJava

Question

I have a method: Observable<List<String>> getNames();
I have object Person with constructors Person() and Person(String name)
Also there is a empty list ArrayList<Person> cachedPersons.

What I need: In my method using RxJava fill array with Person using constructor<String> from List<String> like this:

ArrayList<String> cachedPersons = new ArrayList<Person>();

Observable<List<String>> getNames(){
       Observable.from(getNames())
       .map{
           //cachedPersons.addAll(/*add new Person with corresponding String*/)
           //with List("John","Sara","David")
           //create cachedPersons = List(Person1("John"),Person2("Sara"),Person3("David")) 
       }
    }

Benjamin · Accepted Answer · 2017-12-20 08:53:12Z

4

Observable.from(getNames())
    .map{ name -> new Person(name)}
    .toList()
    .subscribe(
        list -> cachedPersons.addAll(list)
    );

answered Dec 20, 2017 at 8:53

Benjamin

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2 Comments

Stewart Over a year ago

Couldn't you just do Observable.from(getNames()).subscribe(name -> cachedPersons.add(name)); ?

ArsSiegfried Over a year ago

Not sure if i understand correctly, but i still need to return Observable<List<String>> from my function(not List<Person>), and add to cachedPersons "by the way", like inside this stream

Misha Akopov · Accepted Answer · 2017-12-20 18:33:41Z

0

The problem is that you are trying to fill needed ArrayList from map() method, and it is wrong.

It will never be executed until you make a subscription. You are not doing it in your code, so your ArrayList will not be filled with above code.

Do subscription and in subscription onNext you can fill your ArrayList.

answered Dec 20, 2017 at 18:33

Misha Akopov

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Comments

Vasili Fedotov · Accepted Answer · 2017-12-20 22:27:41Z

0

Maybe this

Observable.from(getNames()) 
      .doOnNext(name -> cachedPersons.add(new Person(name)))
      .toList() 
      .subscribe();

This way you are just filling it without changing the stream value.

edited Dec 20, 2017 at 22:27

answered Dec 20, 2017 at 22:20

Vasili Fedotov

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Comments

Ankit Kumar · Accepted Answer · 2017-12-22 02:27:06Z

0

Observable<SourceObjet> source = ...// get first list from here
   source.flatMapIterable(list -> list)
  .map(item -> new ResultsObject().convertFromSource(item))
  .toList()
  .subscribe(transformedList -> ...);

If your Observable emits a List, you can use these operators:

flatMapIterable -> transform your list to an Observable of items
map -> transform your item to another item
toList -> transform a completed Observable to a Observable which emit a list of items from the completed Observable

edited Dec 22, 2017 at 2:27

answered Dec 21, 2017 at 9:33

Ankit Kumar

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2 Comments

yivi Over a year ago

While this code snippet may be the solution, including an explanation really helps to improve the quality of your post. Remember that you are answering the question for readers in the future, and those people might not know the reasons for your code suggestion.

Ankit Kumar Over a year ago

added short description.. @yivi

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