IssueTracker

Component used: LiveData
Version used: 1.0.0 Alpha9-1
Devices/Android versions reproduced on: Moto G3, Android 6.0.1

If you add a LiveData as a source to a MediatorLiveData and then remove it again inside the observer, the source LiveData gets back into active state, even though there shouldn't be any more observers registered to it:


++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
// source LiveData:

MutableLiveData<String> stringData = new MutableLiveData<String>() {
    @Override
    protected void onActive() {
        super.onActive();
        System.out.println("stringData onActive()");
    }

    @Override
    protected void onInactive() {
        super.onInactive();
        System.out.println("stringData onInactive");
    }
};

// receiving MediatorLiveData:

MediatorLiveData<Integer> intData = new MediatorLiveData<>();

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
// In LifecycleOwner:

intData.addSource(stringData, s -> {
        System.out.println("stringData emitted " + s);
        intData.removeSource(stringData);
    });

// note the order here, value of the source LiveData is set before
// observer gets registered:
stringData.setValue("blabla");
intData.observe(this, integer -> {});

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Output:

System.out: stringData onActive()
System.out: stringData emitted blabla
System.out: stringData onInactive
System.out: stringData onActive()

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

As you see, the source LiveData switches back into active state, even though it doesn't have any active observers. This only happens if setValue() is called before registering the LifecycleOwner/Observer.