如何在我的flutter应用程序中添加应用内购买功能？

dependencies:
  in_app_purchase: ^0.5.2

import 'package:in_app_purchase/in_app_purchase.dart';

final InAppPurchaseConnection _iap = InAppPurchaseConnection.instance;
final Set<String> _productIds = {'your_product_id'};
List<ProductDetails> _products = [];

Future<void> initStore() async {
  final bool isAvailable = await _iap.isAvailable();
  if (isAvailable) {
    await _getProducts();
  }
}

Future<void> _getProducts() async {
  Set<String> ids = _productIds;
  ProductDetailsResponse response = await _iap.queryProductDetails(ids);
  _products = response.productDetails;
}

ListView.builder(
  itemCount: _products.length,
  itemBuilder: (BuildContext context, int index) {
    ProductDetails product = _products[index];
    return ListTile(
      title: Text(product.title),
      subtitle: Text(product.description),
      trailing: Text(product.price),
      onTap: () {
        _buyProduct(product);
      },
    );
  },
);

Future<void> _buyProduct(ProductDetails product) async {
  final PurchaseParam purchaseParam = PurchaseParam(productDetails: product);
  await _iap.buyNonConsumable(purchaseParam: purchaseParam);
}

StreamSubscription<List<PurchaseDetails>> _subscription;

void _listenToPurchaseUpdated(List<PurchaseDetails> purchaseDetailsList) {
  purchaseDetailsList.forEach((PurchaseDetails purchaseDetails) async {
    if (purchaseDetails.status == PurchaseStatus.purchased) {
      // 处理购买成功的逻辑
      await _iap.completePurchase(purchaseDetails);
    } else if (purchaseDetails.status == PurchaseStatus.error) {
      // 处理购买失败的逻辑
    }
  });
}

void _startListeningToPurchaseUpdated() {
  _subscription = _iap.purchaseUpdatedStream.listen((List<PurchaseDetails> purchaseDetailsList) {
    _listenToPurchaseUpdated(purchaseDetailsList);
  });
}

void _cancelSubscription() {
  _subscription.cancel();
}