FirebaseResourceLiveData.kt

open class FirebaseResourceLiveData : LiveData<Resource<DataSnapshot>> {
    
    init {
        value = Resource.Loading()
    }
    
    constructor(path: String) {
        query = FirebaseDatabase.getInstance().getReference(path)
    }

    constructor(ref: DatabaseReference) {
        query = ref
    }

    constructor(query: Query) {
        this.query = query
    }

    private val listener = MyValueEventListener()
    private val query: Query

    override fun onActive() {
        value = Resource.Loading(value?.extractData)
        query.addValueEventListener(listener)
    }

    override fun onInactive() {
        query.removeEventListener(listener)
    }

    private inner class MyValueEventListener : ValueEventListener {

        override fun onDataChange(dataSnapshot: DataSnapshot) {
            value = Resource.Success(dataSnapshot)
        }

        override fun onCancelled(databaseError: DatabaseError) {
            val e = databaseError.toException()
            value = Resource.Failure(e)
        }

    }

}