cart如何在使用firebase作为后端react本机应用程序中工作

import firebase from 'firebase/app';
import 'firebase/database';

const firebaseConfig = {
  apiKey: "YOUR_API_KEY",
  authDomain: "YOUR_AUTH_DOMAIN",
  databaseURL: "YOUR_DATABASE_URL",
  projectId: "YOUR_PROJECT_ID",
  storageBucket: "YOUR_STORAGE_BUCKET",
  messagingSenderId: "YOUR_MESSAGING_SENDER_ID",
  appId: "YOUR_APP_ID"
};

if (!firebase.apps.length) {
  firebase.initializeApp(firebaseConfig);
}

{
  "carts": {
    "userId1": {
      "items": [
        { "productId": "product1", "quantity": 2 },
        { "productId": "product2", "quantity": 1 }
      ]
    }
  }
}

const addToCart = (userId, productId, quantity) => {
  const cartRef = firebase.database().ref(`carts/${userId}/items`);
  cartRef.once('value', snapshot => {
    const items = snapshot.val() || [];
    const existingItem = items.find(item => item.productId === productId);

    if (existingItem) {
      existingItem.quantity += quantity;
    } else {
      items.push({ productId, quantity });
    }

    cartRef.set(items);
  });
};

const removeFromCart = (userId, productId) => {
  const cartRef = firebase.database().ref(`carts/${userId}/items`);
  cartRef.once('value', snapshot => {
    const items = snapshot.val() || [];
    const updatedItems = items.filter(item => item.productId !== productId);
    cartRef.set(updatedItems);
  });
};

import React, { useEffect, useState } from 'react';
import { View, Text, FlatList } from 'react-native';

const CartScreen = ({ userId }) => {
  const [cartItems, setCartItems] = useState([]);

  useEffect(() => {
    const unsubscribe = firebase.database().ref(`carts/${userId}/items`).on('value', snapshot => {
      const items = snapshot.val() || [];
      setCartItems(items);
    });

    return () => unsubscribe();
  }, [userId]);

  return (
    <View>
      <FlatList
        data={cartItems}
        keyExtractor={(item, index) => index.toString()}
        renderItem={({ item }) => (
          <View>
            <Text>{item.productId} - Quantity: {item.quantity}</Text>
          </View>
        )}
      />
    </View>
  );
};

export default CartScreen;

const updateCartItem = (userId, productId, quantity) => {
  const cartRef = firebase.database().ref(`carts/${userId}/items/${productId}`);
  cartRef.transaction(currentItem => {
    if (currentItem) {
      currentItem.quantity += quantity;
    } else {
      return { productId, quantity };
    }
    return currentItem;
  });
};