如何将相同的值分组到 1 个 recyclerview 项目中？

Question

I have a recyclerview where I list expenses' category from Firebase using JAVA, I am looking to group categories so I only get 1 recyclerview item called FOOD, ENTERTAINMENT etc, this and the total amount for every item in that category.

this is my recyclerview result now;

this is my adapter class;

public class CategoriesAdapter extends RecyclerView.Adapter<CategoriesAdapter.ViewHolder> {
    private Context mContext;
    private ArrayList<Expense> categories;

    public CategoriesAdapter(Context mContext, ArrayList<Expense> categories) {
        this.mContext = mContext;
        this.categories = categories;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(mContext).inflate(R.layout.categories_retrieve_layout, parent, false);
        return new ViewHolder(view);
    }

    @SuppressLint("SetTextI18n")
    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        final Expense expense = categories.get(position);

        holder.category.setText("" + expense.getCategory());
        holder.amount.setText("$ " + formatNumberCurrency(String.valueOf(expense.getAmount())));

    }

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

    public class ViewHolder extends RecyclerView.ViewHolder {

        private TextView category;
        private TextView amount;
        private TextView percentage;

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

            category = itemView.findViewById(R.id.category_name);
            amount = itemView.findViewById(R.id.category_total_amount);
            percentage = itemView.findViewById(R.id.percentage_indicator);

        }
    }

    private static String formatNumberCurrency(String amount) {
        DecimalFormat formatter = new DecimalFormat("###,###,###");
        return formatter.format(Double.parseDouble(amount));
    }
}

and here is how I am reading my data

final Calendar c = Calendar.getInstance();
@SuppressLint("SimpleDateFormat") DateFormat dateFormat = new SimpleDateFormat("dd-MM-yyyy");
String date = dateFormat.format(c.getTime());

DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference().child("Expenses").child(Objects.requireNonNull(mAuth.getCurrentUser()).getUid());
Query query = databaseReference.orderByChild("date").equalTo(date);
query.addValueEventListener(new ValueEventListener() {
    @SuppressLint("NotifyDataSetChanged")
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        expenses.clear();

        for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
            Expense expense = dataSnapshot.getValue(Expense.class);
            expenses.add(expense);
        }

        categoriesAdapter.notifyDataSetChanged();

    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {

    }
});

Here, the output I am expecting to get

any advice on how to create the logic for this?

---

This is the error I got while trying to use Sambhav. K's answer:

Answer 1

You can check if a value already exists or not when adding it to the list. Try this:

query.addValueEventListener(new ValueEventListener() {
    @SuppressLint("NotifyDataSetChanged")
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        expenses.clear();

        for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
            Expense expense = dataSnapshot.getValue(Expense.class);
            boolean exists = false;
            int count = 0;
            for(int i = 0; i < expenses.size(); i++){
               count = i;
               exists = expenses.get(i).getCategory().equalsIgnoreCase(expense.getCategory());
               if(exists) break;
            }
            if(exists){
               expenses.get(count).setAmount(expenses.get(i).getAmount()() + expense.getAmount());
            }else{
               expenses.add(expense);
            }
        }

        categoriesAdapter.notifyDataSetChanged();

    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {
       error.printStackTrace();
    }
});