How to observe when fragments initialized RxJava/RxAndroid?

Question

I have two fragments and each of them have Publish Subject that on initialization call onNext(true) in onResume(). I want to combine these two Subjects and call some method in third class when they both return true. Do i need to use Observable for this? I cannot find appropriate operation, zip does not work because these are Subjects. How can i combine these?

Answer 1

A subject is both a Observer and a Observable., so you can use zip operator, even with a subject.

What you can do, is using zip with filter operator.

    Subject<Boolean, Boolean> sub1 = PublishSubject.create();
    Observable<Boolean> filter1 = sub1.filter((e) -> e); // filter only event is true

    Subject<Boolean, Boolean> sub2 = PublishSubject.create();
    Observable<Boolean> filter2 = sub2.filter((e) -> e);  // filter only event is true


    Observable.zip(filter1, filter2, (one, two) -> true).subscribe()

If you just want to know if each fragment is initialized, maybe you can emit fragment instead to get a contract like : if view emitted, then it's ready.

class Fragment1 {
    Subject<Fragment, Fragment> sub1 = PublishSubject.create();

    public void onResume() {
         sub1.onNext(this);                
    }

}

class Fragment2 {
    Subject<Fragment, Fragment> sub1 = PublishSubject.create();

    public void onResume() {
         sub1.onNext(this);                
    }

}


class MyView {

     public onCreate() {
         Observable.zip(sub1, sub2, (one, two) -> true).subscribe((b) -> // dosomething)
     }


 }