gistfile1.kt

class FirestoreViewModel : ViewModel(){

    val TAG = "FIRESTORE_VIEW_MODEL"
    var firebaseRepository = FirestoreRepository()
    var savedAddresses : MutableLiveData<List<AddressItem>> = MutableLiveData()

    // save address to firebase
    fun saveAddressToFirebase(addressItem: AddressItem){
        firebaseRepository.saveAddressItem(addressItem).addOnFailureListener {
            Log.e(TAG,"Failed to save Address!")
        }
    }

    // get realtime updates from firebase regarding saved addresses
    fun getSavedAddresses(): LiveData<List<AddressItem>>{
        firebaseRepository.getSavedAddress().addSnapshotListener(EventListener<QuerySnapshot> { value, e ->
            if (e != null) {
                Log.w(TAG, "Listen failed.", e)
                savedAddresses.value = null
                return@EventListener
            }

            var savedAddressList : MutableList<AddressItem> = mutableListOf()
            for (doc in value!!) {
                var addressItem = doc.toObject(AddressItem::class.java)
                savedAddressList.add(addressItem)
            }
            savedAddresses.value = savedAddressList
        })

        return savedAddresses
    }

    // delete an address from firebase
    fun deleteAddress(addressItem: AddressItem){
        firebaseRepository.deleteAddress(addressItem).addOnFailureListener {
            Log.e(TAG,"Failed to delete Address")
        }
    }

}

Hi there! I code in Java and I am having a difficult time in comprehending that FOR loop. I am not able to understand the variables used and if the loop is a normal one or a foreach loop. Thank you!

Hi there! I code in Java and I am having a difficult time in comprehending that FOR loop. I am not able to understand the variables used and if the loop is a normal one or a foreach loop. Thank you!

the loop is foreach one.. It can also be written in Kotlin as

value.forEach { doc -> 
        var addressItem = doc.toObject(AddressItem::class.java)
        savedAddressList.add(addressItem)
}

or in java as

for ( QueryDocumentSnapshot doc : value) {
        AddressItem addressItem  = doc.toObject(AddressItem.class)
       savedAddressList.add(addressItem)
}

What is the variable "value"?

value is QuerySnapshot

for ( QueryDocumentSnapshot doc : value) { AddressItem addressItem = doc.toObject(AddressItem.class) savedAddressList.add(addressItem) }
This shows an error: addSnapshotListener cannot be applied to QuerySnapshots

DO you have the solution?

can you post your whole code? there might be just mis-matching of value types

Also follow this sample code

db.collection("cities")
        .whereEqualTo("state", "CA")
        .addSnapshotListener(new EventListener<QuerySnapshot>() {
            @Override
            public void onEvent(@Nullable QuerySnapshot value,
                                @Nullable FirebaseFirestoreException e) {
                if (e != null) {
                    Log.w(TAG, "Listen failed.", e);
                    return;
                }

                List<String> cities = new ArrayList<>();
                for (QueryDocumentSnapshot doc : value) {
                    if (doc.get("name") != null) {
                        cities.add(doc.getString("name"));
                    }
                }
                Log.d(TAG, "Current cites in CA: " + cities);
            }
        });