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Version: 7.0

Purchase Flow

Source Code: purchase_flow_screen.dart

This example demonstrates how to implement a complete in-app purchase flow for consumable and non-consumable products.

Key Features​

  • Initialize connection to the store
  • Fetch available products
  • Handle purchase requests
  • Listen to purchase events
  • Finish transactions properly

Implementation Overview​

1. Set Up Listeners​

StreamSubscription<Purchase>? _purchaseUpdatedSubscription;
StreamSubscription<PurchaseError>? _purchaseErrorSubscription;

@override
void initState() {
  super.initState();
  _setupListeners();
  _initConnection();
}

void _setupListeners() {
  _purchaseUpdatedSubscription = iap.purchaseUpdatedListener.listen(
    (purchase) {
      debugPrint('Purchase: ${purchase.productId}');
      _handlePurchase(purchase);
    },
  );

  _purchaseErrorSubscription = iap.purchaseErrorListener.listen(
    (error) {
      debugPrint('Error: ${error.code} - ${error.message}');
      _handleError(error);
    },
  );
}

@override
void dispose() {
  _purchaseUpdatedSubscription?.cancel();
  _purchaseErrorSubscription?.cancel();
  super.dispose();
}

2. Initialize Connection​

Future<void> _initConnection() async {
  await iap.initConnection();
  debugPrint('IAP connection initialized');

  // Load products after connection
  await _loadProducts();
}

3. Fetch Products​

final result = await iap.fetchProducts(
  skus: ['product_id_1', 'product_id_2'],
  type: ProductQueryType.InApp,
);

if (result is FetchProductsResultProducts) {
  final products = result.value ?? [];
  debugPrint('Loaded ${products.length} products');
}

4. Request Purchase​

await iap.requestPurchase(
  RequestPurchaseProps.inApp((
    ios: RequestPurchaseIosProps(
      sku: 'product_id',
      quantity: 1,
    ),
    android: RequestPurchaseAndroidProps(
      skus: ['product_id'],
    ),
    useAlternativeBilling: null,
  )),
);

5. Handle Purchase Updates​

Future<void> _handlePurchase(Purchase purchase) async {
  // 1. Verify purchase on server (recommended)
  final isValid = await verifyPurchaseOnServer(purchase);
  if (!isValid) return;

  // 2. Deliver content to user
  await deliverContent(purchase.productId);

  // 3. Finish transaction
  await iap.finishTransaction(
    purchase: purchase,
    isConsumable: true, // Set based on product type
  );
}

6. Handle Purchase Errors​

void _handleError(PurchaseError error) {
  // Don't show error for user cancellation
  if (error.code == ErrorCode.UserCancelled) {
    return;
  }

  // Show error message to user
  showErrorMessage('Purchase failed: ${error.message}');
}

Purchase Validation​

Future<void> _handlePurchase(Purchase purchase) async {
  // IMPORTANT: Server-side receipt validation should be performed here
  // Send the receipt to your backend server for validation
  final isValid = await validateReceiptOnServer(purchase.purchaseToken);

  if (!isValid) {
    showMessage('Receipt validation failed');
    return;
  }

  // After successful server validation, finish the transaction
  await iap.finishTransaction(
    purchase: purchase,
    isConsumable: true, // For consumable products
  );
}

Best Practices​

  1. Always set up listeners before initConnection - Prevents missing purchase events
  2. Verify purchases server-side - Validate receipts with your backend before granting access
  3. Finish transactions properly - Call finishTransaction() after successful validation
  4. Handle user cancellation gracefully - Check for ErrorCode.UserCancelled
  5. Clean up subscriptions - Cancel stream subscriptions in dispose()