RxJava - fetch every item on the list

Question

I have a method that returns an Observable<ArrayList<Long>>, which are ids of some Items. I'd like to go through this list and download every Item using another method that returns Observable<Item>.

How would I do this using RxJava operators?

Answer 1

Here's a small self contained example

public class Example {      public static class Item {         int id;     }      public static void main(String[] args) {         getIds()                 .flatMapIterable(ids -> ids) // Converts your list of ids into an Observable which emits every item in the list                 .flatMap(Example::getItemObservable) // Calls the method which returns a new Observable<Item>                 .subscribe(item -> System.out.println("item: " + item.id));     }      // Simple representation of getting your ids.     // Replace the content of this method with yours     private static Observable<List<Integer>> getIds() {         return Observable.just(Arrays.<Integer>asList(1, 2, 3));     }      // Replace the content of this method with yours     private static Observable<Item> getItemObservable(Integer id) {         Item item = new Item();         item.id = id;         return Observable.just(item);     } } 

Please note that Observable.just(Arrays.<Integer>asList(1, 2, 3)) is a simple representation of Observable<ArrayList<Long>> from your question. You can replace it with your own Observable in your code.

This should give you the basis of what you need.

p/s : Use flatMapIterable method for this case since it belongs to Iterable as explained below:

/**  * Implementing this interface allows an object to be the target of  * the "for-each loop" statement. See  * <strong>  * <a href="{@docRoot}openjdk-redirect.html?v=8&path=/technotes/guides /language/foreach.html">For-each Loop</a>  * </strong>  *  * @param <T> the type of elements returned by the iterator  *  * @since 1.5  * @jls 14.14.2 The enhanced for statement   */  public interface Iterable<T>