How to convert a Map into arrayList from firestore document

问题

My goal is to get query a collection and get the documents each document has three or five hashmap in it .my aim is to get the documents with different id's and populate in nested recycler view . But i facing trouble in converting the map values into arraylist

My Main Model class:

public class BattleGroupPosts {

private String userId;
public ArrayList<PostBattle> userPost;

public BattleGroupPosts() {
} ///below there getters and setters and constructions are there

My PostBattle Modelclass:

public class PostBattle {

private String id;
private String imageuri;
private String description;
private String publisher;
private String tags;
private String challenge_tittle;
private int NumberOfLikesPoints;
private int battle_post_count;
private long TimeLimit;
private Boolean post_time_done;
private @ServerTimestamp
Date timestamp;

public PostBattle() {
} //below the getter and setter and constructor

Querying from firestore:

private List<BattleGroupPosts> battleGroupPosts;
private ArrayList<PostBattle> battlePostLists;

    private void GettingAllBattleGroupPosts(){
    battleGroupPosts = new ArrayList<>();
    battlePostLists = new ArrayList<>();
    adapter = new BattlGroupAdapter(mContext,battleGroupPosts);//Setting the adapter
    battle_posts.setAdapter(adapter);


    CollectionReference GroupIdRef = mFirestore
            .collection("OpenBattle")
            .document(BattlesPost_creator)
            .collection("BattlePost")
            .document(BattlePost_id)
            .collection("Participants");
    GroupIdRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @RequiresApi(api = Build.VERSION_CODES.N)
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {
            if (task.isSuccessful()) {
                for (QueryDocumentSnapshot document : task.getResult()) {
                    Log.d(TAG, document.getId() + " => " + document.getData());

                    final BattleGroupPosts groupPosts = document.toObject(BattleGroupPosts.class);
                    groupPosts.setUserId(groupPosts.getUserId());


                    groupPosts.setUserPosts(battlePostLists);

                    Map<String, PostBattle> batPost = (Map<String, PostBattle>) document.get("userPost1"); 

I get stuck here i don't know how to to add these to array list in the model class i tried converting hashMap to arraylist but my images getting populated with all items Id's in recylerview as it is in the for loop i guess. my method try:

List<PostBattle> newList = new ArrayList<PostBattle>(batPost.values());

                    Log.d(TAG, "onComplete: liisd:" + newList.get(0));
                    PostBattle postBattle = new PostBattle();
                    postBattle.setImageuri(String.valueOf(newList.get(1)));
                    postBattle.setNumberOfLikesPoints(Integer.valueOf(String.valueOf(newList.get(2))));

                    battlePostLists.add(postBattle);

                    battleGroupPosts.add(groupPosts);

                    adapter.notifyDataSetChanged(); ///These methods i did it inside for the loop  

Have tried this :

                    PostBattle postBattle = new PostBattle();

                    Object value = batPost.get("imageuri");

                    postBattle.setImageuri(String.valueOf(value));
                     Log.d(TAG, "onComplete: value: " + value);
                     battlePostLists.add(postBattle);

                    groupPosts.setUserPosts(battlePostLists);

                    battleGroupPosts.add(groupPosts);

                    adapter.notifyDataSetChanged();

And this too:

    Map<String, Object> idMaps = document.getData();
                    for (Map.Entry<String, Object> id : idMaps.entrySet()){
                        String userId = id.getKey();

                        Object yourObject = id.getValue();

                        Log.d(TAG, "onComplete: IDSSS: " + userId);
                        Log.d(TAG, "onComplete: Object: " + yourObject);
                        

                        Map<String, PostBattle> batPost = (Map<String, PostBattle>) document.get("userPost1");

                        PostBattle postBattle = new PostBattle();
                        Object value = batPost.get("imageuri");
                        postBattle.setImageuri(String.valueOf(value));
                        batPost.clear();

                        battlePostLists.add(postBattle);

回答1:

It looks like you want to parse the map to get values, you can do this for multiple keys:

for (Map.Entry<String, PostBattle> params : batPost.entrySet()) {
     if (params.getKey().equals("imageuri")) { // or something else
//add to your arraylist  

                                    }
}

or if you require only one:

String imageuri = batPost.getKey("imageuri").toString();

add the above image uri to your arraylist

If you want to seperate on basis of ids:

Map<String, yourobject> idmaps = document.getData();
for (Map.Entry<String, yourobject> id : idmaps.entrySet()) {
// do your code here
// first get the id 
String userid = id.getKey();

//then do what you have done above
yourobject = id.getValue();

// do your logic on above object this will seperate your userids

}

来源：https://stackoverflow.com/questions/63295921/how-to-convert-a-map-into-arraylist-from-firestore-document