How to reset a BehaviorSubject - stream

Question

I have a BehaviorSubject that I would like to reset - by that I mean I want the latest value to not be available, just as if it was just created.
I don't seem to see an API to do this but I suppose there is another way to achieve the same result?
My desired behavior is that I need to emit events, and I'd like subscribers to get the latest event when they subscribe - if a particular manager is in a 'started' state. But when this manager is 'stopped' the latest event should not be available (just like if it was never started in the first place).

Answer 1

I assume you want to clear the BehaviorSubject (because otherwise don't call onComplete on it). That is not supported but you can achieve a similar effect by having a current value that is ignored by consumers:
public static final Object EMPTY = new Object();
BehaviorSubject<Object> subject = BehaviorSubject.createDefault(EMPTY);
Observable<YourType> obs = subject.filter(v -> v != EMPTY).cast(YourType.class);
obs.subscribe(System.out::println);
// send normal data
subject.onNext(1);
subject.onNext(2);
// clear the subject
subject.onNext(EMPTY);
// this should not print anything
obs.subscribe(System.out::println);

Answer 2

Another method of switching the value of an observable on and off is to use switchMap() to flip between the actual observable and an empty one.
Let's assume you have a manager object, and it has a observable that shows its state. Then,
subjectObservable = manager.getStateObservable()
.switchMap( state -> state == ON ? subject : Observable.never() );
will only emit values while the manager is in the ON state.

Answer 3

Just use setTimeout like this:
setOtpoint(value) {
this._setOption.next(value);
// Clear BehaviorSubject after emit value
setTimeout(() => {
this._setOption.next(null);
}, 100);
}

Answer 4

I find out a better solution for some cases and is:
subject.skiplast(1)
it can work to clean the last position on stream that is being retained because of the BehaviorSubject "behavior"

Answer 5

A problem with #akarnokd's answer is that the .cast prevents YourType from being an interface or a generic type such as List<String>.
Another option is to filter on a boolean field that you can switch on and off.
private BehaviorSubject<PandoraApp> subject = BehaviorSubject.create();
private boolean enabled = true;
Observable<PandoraApp> observable = subject.filter(v -> enabled);
If methods are being called on different threads you can use AtomicBoolean for the filter flag.

Answer 6

Here is my lib for this:
implementation "com.github.kolyall:rxjava2-empty:1.0.36"
Example:
private val myBehaviorSubject = BehaviorSubjectOptional.createOptional<MyItem?>()
errorBehaviorSubject.toObservable()
.subscribe{ item-> Log.d("onNext1", "item = $item")}
var item:MyItem? = MyItem()
myBehaviorSubject.onNextOptional(item)
//For reset:
myBehaviorSubject.clear()
//OR
item = null
myBehaviorSubject.onNextOptional(item)
errorBehaviorSubject.toObservable()
.subscribe{ item-> Log.d("onNext2", "item = $item")}