Convert Firebase field array to list

Question

I'm trying to convert a field which has an array in Firebase Cloud Firestore. The field is stored in a document and contains 10 values in the field.

I can get the data using the following code however I would like to know if its possible to convert this data into a List?

public void getAllowedPostcodes(){
    DocumentReference docRef = 
db.collection("AllowedPostcodes").document("tmGzpfFPFTwGw28uS8y1");

    docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
        @Override
        public void onComplete(@NonNull Task<DocumentSnapshot> task) {
            if (task.isSuccessful()) {
                DocumentSnapshot document = task.getResult();
                if (document != null) {
                    Log.d(TAG, "DocumentSnapshot data: " + task.getResult().getData());

                } else {
                    Log.d(TAG, "No such document");
                }
            } else {
                Log.d(TAG, "get failed with ", task.getException());
            }
        }
    });
}

I have tried the following however, it doesn't compile saying:

"Cannot resolve constructor 'ArrayList(java.util.Map<java.lang.String,java.lang.Object>)"

This is my code:

List<String> allowedData = new ArrayList<String>(task.getResult().getData());

The database structure is as follows:

try using new ArrayList<String>((List)task.getResult().getData().values()); — Rosário P. Fernandes
– Rosário P. Fernandes, Commented Feb 27, 2018 at 19:58
Thanks for the suggestion @RosárioPereiraFernandes. Unfortunately it doesn't work. It throws the following error: java.lang.ClassCastException: java.util.HashMap$Values cannot be cast to java.util.List — Matt List
– Matt List, Commented Feb 27, 2018 at 20:26

Rosário P. Fernandes · Accepted Answer · 2018-02-27 20:42:32Z

2

Create a forEach loop to iterate through each field, cast it to String and add it to the ArrayList:

docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
            @Override
            public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                if (task.isSuccessful()) {
                    DocumentSnapshot document = task.getResult();
                    if (document != null) {
                        Log.d(TAG, "DocumentSnapshot data: " + task.getResult().getData());
                        for(Object item : task.getResult().getData().values())
                            allowedData.add(item.toString());
                    } else {
                        Log.d(TAG, "No such document");
                    }
                } else {
                    Log.d(TAG, "get failed with ", task.getException());
                }
            }
        });

edited Feb 27, 2018 at 20:42

answered Feb 27, 2018 at 20:29

Rosário P. Fernandes

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3 Comments

Matt List Over a year ago

Thanks. That still gives me an exception: java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.lang.String

Matt List Over a year ago

I managed to get it to work using for(Object item : task.getResult().getData().values()) { allowedData.add(item.toString());

Rosário P. Fernandes Over a year ago

Glad you did. I was gonna suggest that next :) .. I've updated my answer to match it

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