问题
The following code emits items from observable1 only after observable2 is completed.
observable1.startWith(observable2)
.subscribe()
I need to achieve another behavior
observable1 -> 0 1 2 3
observable2 -> 1 2 3 4 5 6
observable1.startWithDefault(observable2)
-> 1 2 0 1 2 3
The second observable emits items only while first observable is empty and then items from first one are emited.
I could not find correct solution using only basic operators, what is correct RxJava 2 implementation of custom operator startWithDefault should look like?
P.S.
observable1.subscribe()
observable2.takeUntil(observable1).subscribe()
is not correct solution because of race in case of immediate emit from observable1
回答1:
The direction was good, but you need publish(Function) to share observable1's signals and concatEager to not lose elements from it when the switch appens:
observable1.publish(o ->
Observable.concatEager(observable2.takeUntil(o), o)
)
.subscribe(...)
来源：https://stackoverflow.com/questions/45173252/rxjava-tricky-startwithobservable