recyclerview uploads items multiple time on refresh

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I have implemented a recyclerview, where I want to show the groups that have been created in the app. Right now I am refreshing the recyclerview using the swipeRefreshLayout, but everytime I refresh the recyclerview, it prints out the same group multiple times according to how many times I refresh it.

Can anyone help me solve this problem?

Below is the code.

onCreateView method:

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    Log.d(TAG, "onCreateView: started");
    View view = inflater.inflate(R.layout.fragment_projects, container, false); //This inflates the project_fragment layout to this java class.

    swipeRefreshLayout = view.findViewById(R.id.swipeRefresh);

    add_btn = view.findViewById(R.id.add_project_btn);
    add_btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            requestNewGroup();
        }
    });

    initRecyclerView(view);
    recyclerUpdater();

    swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
        @Override
        public void onRefresh() {
            recyclerUpdater();
            swipeRefreshLayout.setRefreshing(false);
        }
    });
    return view;
}

recyclerUpdate function, where Strings are added to the recyclerView adapter:

 private void recyclerUpdate() {
    if(user != null) {
        firebaseFirestore.collection("users").document(user.getUid()).collection("Groups").get()
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()) {
                            for (QueryDocumentSnapshot document : task.getResult()) {
                                String title = document.getString(TITLE);
                                String groupId = document.getString(GROUP_ID);
                                mProjects.add(title);
                                mProjectsId.add(groupId);
                            }
                            projectAdapter.setItems(mProjects, mProjectsId, getActivity());
                            projectAdapter.notifyDataSetChanged();
                            Log.d(TAG, "onComplete: list: " + mProjects.toString());
                        } else {
                            Log.d(TAG, "onComplete: error getting documents", task.getException());
                        }
                    }
                });
    }
}

recyclerViewAdapter:

public class groupView extends RecyclerView.Adapter<groupView.ViewHolder>{

private static final String TAG = groupView.class.getSimpleName();
private List<String> mItems = new ArrayList<>();
private List<String> mIds = new ArrayList<>();
private Context mContext;

public void setItems(List<String> items, List<String> ids, Context context) {
    mItems = items;
    mIds = ids;
    mContext = context;
}

@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    if(viewType == 0){
        return ViewHolder.inflate(parent);
    }else{
        return null;
    }

}

@Override
public void onBindViewHolder(@NonNull ViewHolder holder, final int position) {
    Log.d(TAG, "onBindViewHolder: called");
    if (holder instanceof ViewHolder) {
        ((ViewHolder) holder).bind(mItems.get(position));
        ((ViewHolder) holder).mLinearLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Log.d(TAG, "onClick: clicked on: " + mItems.get(position));
                //Sending ID as an intent, to be used in the process
                Intent intent = new Intent(mContext, projectClicked.class);
                intent.putExtra("itemPos", mItems.get(position));
                intent.putExtra("itemID", mIds.get(position));
                //intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); //close activitys before calling a new
                mContext.startActivity(intent);
            }
        });
    }


}

@Override
public int getItemCount() {
    return mItems.size();
}

@Override
public int getItemViewType(int position) {
    return 0;
}

static class ViewHolder extends RecyclerView.ViewHolder{

    private TextView mTextView;
    private LinearLayout mLinearLayout;

    public static ViewHolder inflate(ViewGroup parent) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.layout_listitem_group, parent,false);
        return new ViewHolder(view);
    }

    public ViewHolder(@NonNull View itemView) {
        super(itemView);

        mTextView = itemView.findViewById(R.id.list_groups_title);
        mLinearLayout = itemView.findViewById(R.id.listitem_groups);
    }

    public void bind(String text){
        mTextView.setText(text);
    }
}

}

Thank you in advance!

Answer

You are adding new items to mProjects and mProjectsId not clearing these lists. Add clear() before for loop:

if (task.isSuccessful()) {
   mProjects.clear();
   mProjectsId.clear();
   for (QueryDocumentSnapshot document : task.getResult()) {
   ...


Source: stackoverflow