addObserver
Adds a LifecycleObserver that will be notified when the LifecycleOwner changes state.
The given observer will be brought to the current state of the LifecycleOwner. For example, if the LifecycleOwner is in State.STARTED state, the given observer will receive Event.ON_CREATE, Event.ON_START events.
Parameters
observer
The observer to notify.