FirebaseLiveData.kt

inline fun <reified T> DatabaseReference.toLiveData(): LiveData<T> {
    val liveData: MutableLiveData<T> = MutableLiveData()
    addValueEventListener(object : ValueEventListener {
        override fun onDataChange(dataSnapshot: DataSnapshot) {
            dataSnapshot.children.forEach {
                liveData.value = it.getValue<T>(T::class.java)
            }
        }

        override fun onCancelled(databaseError: DatabaseError) {
            Log.e("DatabaseError", "DatabaseError: " + databaseError.message)
        }
    })
    return liveData
}

fun getUsers(): LiveData<User> = usersRef.toLiveData<User>()