in_app_purchase_watchos 0.1.1

watchOS implementation of the in_app_purchase plugin, using dart:ffi over StoreKit to query products and run purchases through SKPaymentQueue.

in_app_purchase_watchos

The watchOS implementation of in_app_purchase, over dart:ffi (StoreKit). Started from a flutter-watchos plugin port scaffold of in_app_purchase_storekit; see PORTING_REPORT.md for the API map.

Usage

Add this package alongside in_app_purchase:

dependencies:
  in_app_purchase: ^3.3.1
  in_app_purchase_watchos: ^0.1.0

That is all. Use the standard in_app_purchase API — no watchOS-specific setup:

final bool available = await InAppPurchase.instance.isAvailable();
final ProductDetailsResponse response =
    await InAppPurchase.instance.queryProductDetails(<String>{'my_product'});

Why this package does something unusual at registration

The app-facing in_app_purchase package does not honour the plugin registrant: it picks an implementation from defaultTargetPlatform and assigns it unconditionally the first time InAppPurchase.instance is read. watchOS reports as TargetPlatform.iOS, so that would install the iOS StoreKit method-channel implementation over this one — and method channels do not exist on watchOS, so every call would fail with channel-error.

That selection runs exactly once and is then memoised, so registerWith() triggers it during plugin registration and installs this implementation afterwards. The app's later reads return the memoised object without re-registering, and every InAppPurchase method resolves InAppPurchasePlatform.instance at call time, so this implementation stays live.

Because the registrant runs before main() creates the binding, the first attempt can fail (upstream installs a pigeon handler, which needs a binding); it is retried on subsequent event-loop turns, well before any widget builds. A host that starts main() late, as flutter-watchos test -d does, is covered by further retries every 10 ms for up to ten seconds.

example/integration_test/registration_test.dart verifies this end to end on a watch: the plain InAppPurchase API reaches StoreKit through FFI with no app-side setup.

Status

Working, and verified end to end on a watch (see below). StoreKit purchasing is available on watchOS (from 6.2), but the StoreKit UI surfaces (SKStoreProductViewController, the review prompt, code redemption) do not exist on the watch and are intentionally out of scope.

Implemented:

• ✅ isAvailable — SKPaymentQueue canMakePayments.
• ✅ queryProductDetails — product lookup via SKProductsRequest.
• ✅ Purchase flow — buyConsumable / buyNonConsumable, purchaseStream, completePurchase, restorePurchases via SKPaymentQueue (a transaction observer whose updates are drained into purchaseStream).

Out of scope (no watchOS equivalent): the StoreKit UI surfaces (SKStoreProductViewController, the review prompt, code redemption).

The platform addition: InAppPurchase.instance.getPlatformAddition<InAppPurchaseStoreKitPlatformAddition>() returns InAppPurchaseWatchosPlatformAddition, which extends StoreKit's addition so the upstream cast works. None of its methods is supported on watchOS yet: sync, presentCodeRedemptionSheet, refreshPurchaseVerificationData, setDelegate and showPriceConsentIfNeeded each return a Future that fails with an UnsupportedError. None of them throws when it is called, so code that awaits them inside try/catch, or skips them on the watch, keeps working.

Verified end to end against real StoreKit on a watch simulator, using the bundled watchos/Configuration.storekit test configuration: product lookup returns all four test products, each with its amount, and a purchase completes (buy → purchaseStream reports purchased with a receipt → completePurchase finishes the transaction). Also builds and links on a physical Apple Watch (all 10 FFI symbols present in the device binary).

StoreKit testing only activates when the app is launched from Xcode — the scheme's StoreKit configuration is what turns it on. A CLI launch (flutter-watchos drive) does not enable it, so product lookups return "not found" there; example/integration_test/ skips its product assertions in that case rather than failing. To exercise purchasing, open example/watchos/Runner.xcodeproj and Run.

Example

example/ is the upstream in_app_purchase example app (its demo UI and official integration_test/), ported to watchOS with a runner via flutter-watchos plugin port --include-example. Run it on a watch simulator:

cd example
flutter-watchos drive \
  --driver=test_driver/integration_test.dart \
  --target=integration_test/in_app_purchase_test.dart \
  -d <watch-sim>

The demo exercises the full purchasing flow. On a bare Simulator there are no StoreKit products, so product lookup returns "not found" and a purchase cannot complete — add a .storekit test configuration (or use a sandbox account) to exercise it end to end.

The example's code is in_app_purchase 3.3.1's, unchanged except for these watchOS deviations:

Where	Change	Why
example/lib/main.dart, the four StoreKit addition calls (setDelegate at start and in dispose, the upgrade button, showPriceConsentIfNeeded)	Platform.isIOS becomes FlutterWatchosPlatform.isIos	Platform.isIOS is true on the watch, where those addition methods fail with an UnsupportedError; the example started with an unhandled exception from setDelegate
example/lib/main.dart, the comment above showPriceConsentIfNeeded	reworded	the project's word rule
example/pubspec.yaml	adds flutter_watchos: ^0.1.0 and shared_preferences_watchos: ^0.1.0	for FlutterWatchosPlatform, and so the example's shared_preferences store works on the watch

example/integration_test/watchos_example_start_test.dart is a watchOS test beside the upstream ones: it starts the example and checks that it finishes its store check without an error.

Not supported on watchOS

These members of in_app_purchase_platform_interface 1.4.1 and in_app_purchase_storekit 0.4.13 throw or fail on watchOS. PORTING_REPORT.md lists every member under "Interface coverage".

Member	On watchOS	Why
countryCode	throws UnimplementedError when called	the storefront is not read yet
addition presentCodeRedemptionSheet	fails with an UnsupportedError that names watchOS	StoreKit has no code redemption sheet on watchOS
addition showPriceConsentIfNeeded	fails with an UnsupportedError that names watchOS	StoreKit has no such consent sheet on watchOS
addition sync	fails with an UnsupportedError that names watchOS	not implemented yet (StoreKit 2)
addition refreshPurchaseVerificationData	fails with an UnsupportedError that names watchOS	the receipt refresh is not implemented yet
addition setDelegate	fails with an UnsupportedError that names watchOS	the payment queue delegate is not implemented yet

License

The FlutterWatch Authors under a BSD-3-Clause license. See LICENSE for the full text.