Kotlin wrappers for observing Firebase Firestore database queries and documents using LiveData

FirestoreLiveData.kt

fun Query.observeLiveData(): FirestoreQueryLiveData {
    return FirestoreQueryLiveData(this)
}

fun DocumentReference.observeLiveData(): FirestoreDocumentLiveData {
    return FirestoreDocumentLiveData(this)
}

class FirestoreQueryLiveData(
        private val query: Query
) : LiveData<List<DocumentSnapshot>>() {

    private var listenerRegistration: ListenerRegistration? = null

    override fun onActive() {
        super.onActive()
        logd("onActive $query")
        listenerRegistration = query.addSnapshotListener { snapshot: QuerySnapshot?, exception: FirebaseFirestoreException? ->
            if (exception != null) {
                loge("FirestoreQueryLiveData error", exception)
            } else {
                value = snapshot!!.documents
            }
        }
    }

    override fun onInactive() {
        super.onInactive()
        logd("onInactive $query")
        listenerRegistration?.remove()
    }
}

class FirestoreDocumentLiveData(
        private val documentReference: DocumentReference
) : LiveData<DocumentSnapshot>() {

    private var listenerRegistration: ListenerRegistration? = null

    override fun onActive() {
        super.onActive()
        logd("onActive $documentReference")
        listenerRegistration = documentReference.addSnapshotListener { snapshot: DocumentSnapshot?, exception: FirebaseFirestoreException? ->
            if (exception != null) {
                loge("FirestoreQueryLiveData error", exception)
            } else {
                value = snapshot!!
            }
        }
    }

    override fun onInactive() {
        super.onInactive()
        logd("onInactive $documentReference")
        listenerRegistration?.remove()
    }
}