Interface Observable

void addListener(InvalidationListener listener)

Adds an InvalidationListener which will be notified whenever the Observable becomes invalid. If the same listener is added more than once, then it will be notified more than once. That is, no check is made to ensure uniqueness.

Note that the same actual InvalidationListener instance may be safely registered for different Observables.

The Observable stores a strong reference to the listener which will prevent the listener from being garbage collected and may result in a memory leak. It is recommended to either unregister a listener by calling removeListener after use or to use an instance of WeakInvalidationListener avoid this situation.

void removeListener(InvalidationListener listener)

Removes the given listener from the list of listeners, that are notified whenever the value of the Observable becomes invalid.

If the given listener has not been previously registered (i.e. it was never added) then this method call is a no-op. If it had been previously added then it will be removed. If it had been added more than once, then only the first occurrence will be removed.

default Subscription subscribe(Runnable invalidationSubscriber)

Creates a Subscription on this Observable which calls invalidationSubscriber whenever it becomes invalid. The provided subscriber is akin to an InvalidationListener without the Observable parameter. If the same subscriber is subscribed more than once, then it will be notified more than once. That is, no check is made to ensure uniqueness.

Note that the same subscriber instance may be safely subscribed for different Observables.

Also note that when subscribing on an Observable with a longer lifecycle than the subscriber, the subscriber must be unsubscribed when no longer needed as the subscription will otherwise keep the subscriber from being garbage collected.