Cfrgtkky

I'm new on Google Firebase and I'm trying to learn something about it.
I'm doing an Android app where you can create a group of person and set the title of the group..then, in the "group page", you can see all your group in a listview.
The structure of my firestore db is something like this:

users --> email(document) ---> Group(collection) --> GroupName(Document) and the group name document contains the partecipants arrayList (partecipant 0 : Name1, partecipant1: name2 etc).

I would like to retrieve the document id(which is the group title) and the arrayList of partecipants, but I don't know of to use the for each in the code...

This is my code:

public void load_list_view(){



    String email = getEmail();

    final DocumentReference docRef = db.collection("users").document(email).collection("Group").document();



    docRef.get()

            .addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {

                @Override

                public void onSuccess(DocumentSnapshot documentSnapshot) {





                        titleArray.add(documentSnapshot.getId());

                        titleString = documentSnapshot.getId();



                        partecipantsArray.add(documentSnapshot.getString("partecipant"));

                        num_partecipants =  partecipantsArray.size();

                        numArray.add(num_partecipants);

                        trash = R.drawable.trash_icon;

                        firstChar = Character.toString(titleString.charAt(0));

                        firstCharArray.add(firstChar);

                        customAdapter = new GroupAdapter(GroupActivity.this, firstCharArray, titleArray, numArray, trash);

                        listView.setAdapter(customAdapter);





                }

            })

            .addOnFailureListener(new OnFailureListener() {

                @Override

                public void onFailure(@NonNull Exception e) {

                    Toast.makeText(GroupActivity.this, e.getStackTrace().toString(), Toast.LENGTH_LONG).show();



                }

            });



}

with titleArray.add(documentSnapshot.getId()); it retrieve a random ID and I can't understand why.

I haven't found enough documentation on Internet about Arraylist and firestore.

First of all, to get all the documents in a collection you should write your code differently as shown in this documentation.

db.collection("cities")

    .get()

    .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {

        @Override

        public void onComplete(@NonNull Task<QuerySnapshot> task) {

            if (task.isSuccessful()) {

                for (QueryDocumentSnapshot document : task.getResult()) {

                    Log.d(TAG, document.getId() + " => " + document.getData());

                }

            } else {

                Log.d(TAG, "Error getting documents: ", task.getException());

            }

        }

    });

Secondly, if you are retrieving an ArrayList you should use (ArrayList<String>) documentSnapshot.get("key") instead of documentSnapshot.getString("key").

Thirdly, you are getting random Id because with this line of code (mentioned below) firebase is generating a new document reference with a random id. Reference Link.

    final DocumentReference docRef = db.collection("users").document(email).collection("Group").document();

For your help, I have tweaked your code and you can try this code and check if it's working or not.

public void load_list_view() {



        String email = getEmail();

        final DocumentReference docRef = firestore.collection("users").document(email);



        docRef.collection("Group")

                .get()

                .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {

                    @Override

                    public void onSuccess(QuerySnapshot queryDocumentSnapshots) {

                        for (QueryDocumentSnapshot document : queryDocumentSnapshots) {



                            //Extracting Group name from each document



                            titleString = document.getId();

                            titleArray.add(titleString);



                            //Extracting participants ArrayList from each document



                            partecipantsArray.add((ArrayList<String>) document.get("participant"));

                            numArray.add(num_partecipants);

                            firstChar = Character.toString(titleString.charAt(0));

                            firstCharArray.add(firstChar);



                        }



                        num_partecipants = partecipantsArray.size();

                        numArray.add(num_partecipants);

                        trash = R.drawable.trash_icon;

                        firstChar = Character.toString(titleString.charAt(0));

                        firstCharArray.add(firstChar);

                        customAdapter = new GroupAdapter(GroupActivity.this, firstCharArray, titleArray, numArray, trash);

                        listView.setAdapter(customAdapter);



                    }

                })

                .addOnFailureListener(new OnFailureListener() {

                    @Override

                    public void onFailure(@NonNull Exception e) {

                        //HANDLE EXCEPTION

                    }

                });

    }