Это весь код для корзины я хочу чтобы можно было открыть корзину при нажатии на кнопку: package com.example.myapp_2;

import com.example.myapp_2.List_1.Product;

import java.util.ArrayList;
import java.util.List;

public class Cart {
private static Cart instance;

private List<CartItem> items;

private Cart() {
items = new ArrayList<>();
}

public static Cart getInstance() {
if (instance == null) {
instance = new Cart();
}
return instance;
}

public void addItem(Product product) {
for (CartItem item : items) {
if (item.getProduct().equals(product)) {
item.setQuantity(item.getQuantity() + 1);
return;
}
}
items.add(new CartItem(product, 1));
}

public void updateItem(CartItem item, int newQuantity) {
if (newQuantity <= 0) {
removeItem(item);
} else {
item.setQuantity(newQuantity);
}
}

public void removeItem(CartItem item) {
items.remove(item);
}

public List<CartItem> getItems() {
return items;
}

public void clear() {
items.clear();
}

public double getTotalPrice() {
double totalPrice = 0;
for (CartItem item : items) {
totalPrice += item.getTotalPrice();
}
return totalPrice;
}
}
package com.example.myapp_2;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.List;

public class CartAdapter extends RecyclerView.Adapter<CartItemViewHolder> {

private List<CartItem> items;
private OnCartItemListener listener;

public CartAdapter(List<CartItem> items, OnCartItemListener listener) {
this.items = items;
this.listener = listener;
}

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

@Override
public void onBindViewHolder(CartItemViewHolder holder, int position) {
CartItem item = items.get(position);
holder.bind(item, listener);
}

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

public void setItems(List<CartItem> items) {
this.items = items;
notifyDataSetChanged();
}
}package com.example.myapp_2;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

public class CartFragment extends Fragment {

private TextView totalPriceTextView;
private Button placeOrderButton;
private RecyclerView recyclerView;

private CartAdapter adapter;
private Cart cart;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_cart, container, false);


// инициализируем элементы UI и получаем объект Cart из синглтона
totalPriceTextView = view.findViewById(R.id.total_price_text_view);
placeOrderButton = view.findViewById(R.id.place_order_button);
recyclerView = view.findViewById(R.id.cart_recycler_view);

cart = Cart.getInstance();

adapter = new CartAdapter(cart.getItems(), new OnCartItemListener() {
@Override
public void onQuantityChanged(CartItem item, int newQuantity) {
cart.updateItem(item, newQuantity);
updateTotalPrice(); // обновляем общую стоимость
}

@Override
public void onRemoveButtonClick(CartItem item) {
cart.removeItem(item);
adapter.setItems(cart.getItems());
updateTotalPrice();
}
}); // передаём обработчики событий для кнопок изменения количества и удаления товара

recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));

updateTotalPrice();

placeOrderButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
placeOrder();
}
}); // обработчик кнопки оформления заказа

return view;
}

private void placeOrder() {
// TODO: здесь должен быть код для оформления заказа
}

private void updateTotalPrice() {
double totalPrice = cart.getTotalPrice();
totalPriceTextView.setText(getString(R.string.cart_item_total_price, totalPrice));
}
}

package com.example.myapp_2;

import com.example.myapp_2.List_1.Product;

public class CartItem {
private Product product; // сам товар
private int quantity; // количество

public CartItem(Product product, int quantity) {
this.product = product;
this.quantity = quantity;
}

public Product getProduct() {
return product;
}

public void setProduct(Product product) {
this.product = product;
}

public int getQuantity() {
return quantity;
}

public void setQuantity(int quantity) {
this.quantity = quantity;
}

public double getTotalPrice() {
return product.getPrice() * quantity;
}
}

package com.example.myapp_2;

import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.example.myapp_2.List_1.Product;

public class CartItemViewHolder extends RecyclerView.ViewHolder {

private ImageView productImageView;
private TextView productNameTextView;
private TextView productPriceTextView;
private TextView productTotalPriceTextView;
private TextView productQuantityTextView;
private Button decreaseButton;
private Button increaseButton;
private Button removeButton;
private int quantity;

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

productImageView = itemView.findViewById(R.id.cart_item_image_view);
productNameTextView = itemView.findViewById(R.id.cart_item_name_text_view);
productPriceTextView = itemView.findViewById(R.id.cart_item_price_text_view);
productTotalPriceTextView = itemView.findViewById(R.id.cart_item_total_price_text_view);
productQuantityTextView = itemView.findViewById(R.id.cart_item_quantity_text_view);
decreaseButton = itemView.findViewById(R.id.cart_item_decrease_button);
increaseButton = itemView.findViewById(R.id.cart_item_increase_button);
removeButton = itemView.findViewById(R.id.cart_item_remove_button);
}

public void bind(CartItem item, OnCartItemListener listener) {
Product product = item.getProduct();
quantity = item.getQuantity();

productImageView.setImageResource(product.getImageResource());
productNameTextView.setText(product.getName());
productPriceTextView.setText(itemView.getContext().getString(R.string.product_price, product.getPrice()));
productTotalPriceTextView.setText(itemView.getContext().getString(R.string.cart_item_total_price, item.getTotalPrice()));
productQuantityTextView.setText(String.valueOf(quantity));

decreaseButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
quantity -= 1;
productQuantityTextView.setText(String.valueOf(quantity));
listener.onQuantityChanged(item, quantity);
}
});

increaseButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
quantity += 1;
productQuantityTextView.setText(String.valueOf(quantity));
listener.onQuantityChanged(item, quantity);
}
});

removeButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
listener.onRemoveButtonClick(item);
}
});
}
}
package com.example.myapp_2;

public interface OnCartItemListener {
void onQuantityChanged(CartItem item, int newQuantity);//вызывается при изменении количества товара в корзине
void onRemoveButtonClick(CartItem item);//вызывается при нажатии на кнопку удаления товара из корзины
}
package com.example.myapp_2;

import com.example.myapp_2.List_1.Product;

public interface OnProductClickListener {
void onAddToCartClick(Product product);
}
package com.example.myapp_2;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import com.example.myapp_2.List_1.Product;
import com.example.myapp_2.List_1.ProductAdapter;

import java.util.List;

public class ProductsFragment extends Fragment {
private List<Product> productList;
private RecyclerView recyclerView;
private ProductAdapter adapter;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_products, container, false);

// Здесь инициализируем список товаров и recyclerView

adapter = new ProductAdapter(productList, new OnProductClickListener() {
@Override
public void onAddToCartClick(Product product) {
addToCart(product);
}
}); // передаём метод добавления товара в корзину

recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));

return view;
}

private void addToCart(Product product) {
// метод добавления товара в корзину
Cart cart = Cart.getInstance();
cart.addItem(product);
}
}