java - Update textview from Recyclerview Adapter class

Question

I'm working on a E-commerce App to place some online orders. In my Recyclerview there are products, which are added at the previous activity. Here i'm populating the added products in the Recyclerview with the details such as item name, qty, price etc.. There are buttons to increase/decrease the qty of each products and another button to delete the item too.

At the bottom of the Recyclerview Layout there is another textview to Show the grand total. As I'm handling the button slicks in the RecyclerViewAdapter class, while user updating the qty or deleting an item, I have to update the Grand total. I tried some solutions already mentioned here, but the app crashes at random button clicks. Please provide a solution or a better way to do this.

Here is my Adapter class:

public class InvoiceRecyclerViewAdapter extends RecyclerView.Adapter<InvoiceRecyclerViewAdapter.ViewHolder> {
    private static final String TAG = "RecylerViewAdapter";

    List<Products> addedProductsList;
    Context mContext;


    public InvoiceRecyclerViewAdapter(Context mContext,List<Products> addedProductsList)
    {
        this.mContext=mContext;
        this.addedProductsList=addedProductsList;

    }
    public InvoiceRecyclerViewAdapter(Context mContext)
    {
        this.mContext=mContext;
    }

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

    @Override
    public void onBindViewHolder(@NonNull final ViewHolder holder, final int position) {

        holder.item_qty.setText("1");
        holder.itemname.setText(addedProductsList.get(position).getName());
        holder.itemprice.setText("Rs "+addedProductsList.get(position).getPrice());
        holder.itemdiscount.setText("Rs "+calculate_dis(position));
        holder.itemtotal.setText("Rs "+calculate_total(position));


        holder.button_inc.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int qty = addedProductsList.get(position).getQty();
                qty++;
                addedProductsList.get(position).setQty(qty);
                holder.item_qty.setText(""+qty);
                holder.itemdiscount.setText("Rs "+calculate_dis(position));
                holder.itemtotal.setText("Rs "+calculate_total(position));

                UpdateTotal();

            }
        });

        holder.button_dec.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int qty = addedProductsList.get(position).getQty();
                qty--;
                if(qty>0){
                    addedProductsList.get(position).setQty(qty);
                    holder.item_qty.setText(""+qty);
                    holder.itemdiscount.setText("Rs"+calculate_dis(position));
                    holder.itemtotal.setText("Rs"+calculate_total(position));

                    UpdateTotal();
                }

            }
        });

        holder.button_cancel.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                addedProductsList.get(position).setAddedTocart(false);
                //notifyDataSetChanged();
                addedProductsList.remove(position);
                notifyItemRemoved(position);

                UpdateTotal();
            }
        });
    }

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


    public class ViewHolder extends RecyclerView.ViewHolder{

        TextView itemname,itemtotal,itemprice,itemdiscount,item_qty;
        Button button_cancel,button_inc,button_dec;
        ConstraintLayout parent_layout;

        public ViewHolder(View itemView) {
            super(itemView);
            itemname = itemView.findViewById(R.id.textView_item_name);
            itemprice = itemView.findViewById(R.id.textView_item_price);
            itemdiscount = itemView.findViewById(R.id.textView_item_discount);
            itemtotal = itemView.findViewById(R.id.textView_item_total);
            button_cancel = itemView.findViewById(R.id.button_cancel);
            button_inc=itemView.findViewById(R.id.button_inc);
            button_dec=itemView.findViewById(R.id.button_dec);
            item_qty = itemView.findViewById(R.id.textView_qty);
            parent_layout = itemView.findViewById(R.id.invoice_parent_layout);

        }
    }

    private float calculate_dis(int pos){
        float dis = 0;
        if(addedProductsList.get(pos).isPrice_g_enabled()){
            int qty=addedProductsList.get(pos).getQty();
            dis = Float.parseFloat(addedProductsList.get(pos).getPrice())-Float.parseFloat(addedProductsList.get(pos).getPrice_g());
            dis = qty*dis;
        }
        return dis;


    }
    private float calculate_total(int pos){
        int qty=addedProductsList.get(pos).getQty();
        float price,total;
        if(addedProductsList.get(pos).isPrice_g_enabled()){
            price = Float.parseFloat(addedProductsList.get(pos).getPrice_g());
        }
        else{
            price= Float.parseFloat(addedProductsList.get(pos).getPrice());
        }

        total = price*qty;
        return total;
    }
    private void UpdateTotal(){

        TextView txtView =((EditQuantity)mContext).findViewById(R.id.textView_total);

        float total=0,price=0;
        int qty=0;
        for(int i=0;i<addedProductsList.size();i++){
            if(addedProductsList.get(i).isAddedTocart()) {
                qty = addedProductsList.get(i).getQty();
                if(addedProductsList.get(i).isPrice_g_enabled()){
                    price = Float.parseFloat(addedProductsList.get(i).getPrice_g());
                }
                else{
                    price= Float.parseFloat(addedProductsList.get(i).getPrice());
                }

            }
            total=total+(qty*price);
        }
        txtView.setText("Rs "+total);
    }
}

Here is the Main Activity part:

public class EditQuantity extends AppCompatActivity {

    ArrayList<Products> products_list;
    ArrayList<Products> cart_productslist= new ArrayList<>();
    Products added_product;
    FloatingActionButton fab_next;
    TextView total_textview;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_edit_quantity);

        products_list = getIntent().getParcelableArrayListExtra("products");
        Products products;
        for(int i=0;i<products_list.size();i++){
            products = products_list.get(i);
            if(products.isAddedTocart()){
                added_product = new Products(products.getName(),products.getPrice(),products.getPrice_g(),products.getImage(),1,true,products.isPrice_g_enabled());

                cart_productslist.add(added_product);
            }

        }

        Toolbar toolbar = findViewById(R.id.toolbar_invoice);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("Cart");

        total_textview = findViewById(R.id.textView_total);
        total_textview.setText("Rs "+CalTotal());


        fab_next = findViewById(R.id.fab_next);
        fab_next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        InitRecylerView();
    }

    @Override
    public void onBackPressed() {

    }

    private void InitRecylerView() {
        RecyclerView recyclerView = findViewById(R.id.invoice_recyclerview);
        InvoiceRecyclerViewAdapter adapter = new InvoiceRecyclerViewAdapter(
                this ,cart_productslist);
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

    }

    public float CalTotal(){
        float total=0;
        float i_total,price;
        for(int i=0;i<cart_productslist.size();i++){
            if(cart_productslist.get(i).isAddedTocart()) {
                int qty = cart_productslist.get(i).getQty();
                if(cart_productslist.get(i).isPrice_g_enabled()){
                    price = Float.parseFloat(cart_productslist.get(i).getPrice_g());
                }
                else{
                    price= Float.parseFloat(cart_productslist.get(i).getPrice());
                }
                i_total = price * qty;
                total = total + i_total;
            }
        }
        return total;
    } 

Answer 1

I'd suggest going through a listener, moving your onClickListeners and removing the for loops.

So, step by step

In your adapter class declare an interface

public interface OnQuantityChangeListener {
    void onQuantityChange( float change );
}

Next add a private OnQuantityChangeListener to your adapter class and change the constructor to add one at creation:

private OnQuantityChangeListener mListener;

public InvoiceRecyclerViewAdapter(Context mContext,List<Products> addedProductsList, OnQuantityChangeListener listener) {
    this.mContext=mContext;
    this.addedProductsList=addedProductsList;
    mListener = listener;

}
public InvoiceRecyclerViewAdapter(Context mContext, OnQuantityChangeListener listener)
{
    this.mContext=mContext;
    mListener = listener;
}

It's bad for performance to set OnClickListeners in the onBindViewHolder method, because this means you're going to have to add them any time a view pops up onto the screen. Set them in the onCreateViewHolder method instead, that way you'll recycle them. To get your current item you can use the getAdapterPosition() method.

So in the onCreateViewHolder method set the listeners:

@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.layout_invoice,parent,false);
    ViewHolder viewHolder = new ViewHolder(view);

    viewHolder.button_inc.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Products product = addedProductsList.get(getAdapterPosition());

            product.setQty( product.getQty() + 1 );

            float difference = product.isPrice_g_enabled() ? Float.parseFloat(product.getPrice_g()) : Float.parseFloat(product.getPrice());

            mListener.onQuantityChange( difference );

            notifyItemChanged( getAdapterPosition ):// This will call onBindViewAdapter again and change all your strings for you

        }
    });

    viewHolder.button_dec.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Products product = addedProductsList.get(getAdapterPosition());

            if( product.getQty() == 0 )// Can't remove an item if it's already at 0
                return;

            product.setQty( product.getQty() - 1 );

            float difference = product.isPrice_g_enabled() ? Float.parseFloat(product.getPrice_g()) : Float.parseFloat(product.getPrice());

            mListener.onQuantityChange( -difference );

            notifyItemChanged( getAdapterPosition ):// This will call onBindViewAdapter again and change all your strings for you

        }
    });

    viewHolder.button_cancel.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Products product = addedProductsList.get(getAdapterPosition());

            float difference = product.isPrice_g_enabled() ? Float.parseFloat(product.getPrice_g()) : Float.parseFloat(product.getPrice());

            mListener.onQuantityChange( -difference * product.getQty() );

            product.setQty( 0 );

            notifyItemChanged( getAdapterPosition ):// This will call onBindViewAdapter again and change all your strings for you

            // You decide at this point if you want to remove the item altogether or just show 0

        }
    });

    return viewHolder;
}

Remember at this point to remove the OnClickListeners from your onBindViewHolder method.

Once this is done head over to your Activity and add a private total:

private float total = 0;

and edit your adapter creation like so:

InvoiceRecyclerViewAdapter adapter = new InvoiceRecyclerViewAdapter(
        this ,cart_productslist, new InvoiceRecyclerViewAdapter.OnQuantityChangeListener(){

    @Override
    void onQuantityChange( float difference ){

        total += difference;
        total_textview.setText("Rs "+ total);

    }

} );

And that about does it. Remember to calculate your first total in your activity once (no escaping the for loop here) and then make sure you save your instance states.

Hope this helps!