Change recyclerview rows after being created

Question

I have a viewPager which contains two fragments. First for showing list of products and another one for showing list of selected products. In the second fragment, I can change some properties of order or remove it. When a product is selected (in the first fragment) a checkbox is checked and its correspond Product is added to an array. I can reflect changes to the first fragment via below interface:

public interface IItemSelectionObserver {
    void onItemSelectionChanged(InvoiceItem item, boolean selection_state);
}

The problem is, I update the array of selected products in first fragments but can't update UI. How can I fix UI?

    public class FragmentProducts extends Fragment implements IItemSelectionObserver {
    private ProductAdapter adapter;
    private RecyclerView recyclerView;
    private LinearLayoutManager layoutManager;

    private IItemSelectionObserver observer;
    private static ArrayList<InvoiceItem> selectedProducts = new ArrayList<>();

    public FragmentProducts setObserver(IItemSelectionObserver observer){
            this.observer = observer;
            return this;
    }

    // .
    // .
    // .

    @Override
    public void onItemSelectionChanged(InvoiceItem item, boolean selection_state) {
            if (selection_state){
                    adapter.selectedProductChanged(item);
            }
            else {
                    adapter.deselectProduct(item);
            }
    }
}

The adapter is:

public class ProductAdapter extends RecyclerView.Adapter<ProductAdapter.ProductViewHolder> {
    private ArrayList<Product> products;
    private ArrayList<InvoiceItem> selectedProducts;
    private IItemSelectionObserver observer;
    private RecyclerView mRecyclerView;

    public ProductAdapter(ArrayList<Product> items,
                                      IItemSelectionObserver observer,
                      ArrayList<InvoiceItem> selectedProducts) {
            products = items;
        this.observer = observer;
        this.selectedProducts = selectedProducts;
    }

    public void selectedProductChanged(InvoiceItem item)
    {
        if(selectedProducts.contains(item)){
            int index = selectedProducts.indexOf(item);
            selectedProducts.get(index).setCount(item.getCount());
            notifyDataSetChanged();
        }
    }

    public void deselectProduct(InvoiceItem item){
        if(selectedProducts.contains(item)){
            selectedProducts.remove(item);
            notifyDataSetChanged();
        }
    }

    @Override
    public void onAttachedToRecyclerView(RecyclerView recyclerView) {
        super.onAttachedToRecyclerView(recyclerView);

        mRecyclerView = recyclerView;
    }

    @Override
    public ProductViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View inflatedView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.product_list_item, parent, false);

        return new ProductViewHolder(inflatedView);
    }

    @Override
        public void onBindViewHolder(ProductViewHolder holder, int position) {
        Product product = products.get(position);
        holder.setProduct(product);
    }

    public class ProductViewHolder extends RecyclerView.ViewHolder implements
        View.OnClickListener,
        ChooseQuantityDialog.IChooseQuantityDialogObserver {
            public Product mProduct;

            public Context context;
            public TextView priceTxtView,
                 nameTxtView,
                 quantityTxtView;

            public ImageView productImageView;
            public CheckBox isProductSelected;

            public ProductViewHolder(View itemView) {
            super(itemView);
            itemView.setOnClickListener(this);

            // Init ui
            nameTxtView = (TextView) itemView.findViewById(R.id.name);
            priceTxtView = (TextView) itemView.findViewById(R.id.price);
            quantityTxtView = (TextView) itemView.findViewById(R.id.exist);
            productImageView = (ImageView) itemView.findViewById(R.id.image);
            isProductSelected = (CheckBox) itemView.findViewById(R.id.product_list_item_chckBx_isSelected);
        }

    public void setProduct(Product product) {
        mProduct = product;
        onProductChanged();
    }

    private void onProductChanged() {
        // set view's text and images

    }
}