Mastering StoreKit 2
StoreKit provides us with an opportunity to make revenue from our apps. It allows us to set up the purchase flow for in-app purchases and subscriptions. StoreKit 2 introduces a modern Swift-based API to build type-safe in-app purchases. This week we will start the series of posts about StoreKit 2.
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First, we must configure our project by adding in-app purchases in the projects’ “Signing & Capabilities” tab. Next, we should create a StoreKit configuration file to test in-app purchases without a network connection with the App Store. Go to File -> New -> File and choose “StoreKit Configuration File”.
You can create a local-only configuration file and populate it with test subscriptions and in-app purchases. Another option is to fetch the list of subscriptions and in-app purchases from the App Store Connect by enabling the “Sync this file with an app in App Store Connect” checkbox.
The final step is to run your app with the predefined StoreKit configuration file. You need to edit the scheme of your project, and in the options tab of the run section, choose your StoreKit configuration file. Now you have a fully-configured project allowing us to test in-app purchases in the Xcode.
Let’s start building our paywall feature by introducing the Store type to handle all the logic related to in-app purchases.
import StoreKit
@MainActor final class Store: ObservableObject {
@Published private(set) var products: [Product] = []
init() {}
func fetchProducts() async {
do {
products = try await Product.products(
for: [
"123456789", "987654321"
]
)
} catch {
products = []
}
}
}
As you can see in the example above, we define the Store type fetching and storing the list of products we will display on the paywall screen. The StoreKit 2 framework provides the Product type encapsulating all the logic around an in-app purchase. The Product type has a static function called products that we can use to fetch the list of products by providing a collection of identifiers.
struct ContentView: View {
@StateObject private var store = Store()
var body: some View {
VStack {
if store.products.isEmpty {
ProgressView()
} else {
ForEach(store.products, id: \.id) { product in
Button {
Task {
try await store.purchase(product)
}
} label: {
VStack {
Text(verbatim: product.displayName)
.font(.headline)
Text(verbatim: product.displayPrice)
}
}
.buttonStyle(.borderedProminent)
}
}
}
.task {
await store.fetchProducts()
}
}
}
We use our Store type to fetch and display the list of available in-app purchases. An instance of the Product type contains all information we need to show, like the title, description, and price of an in-app purchase.
The Product type also has the purchase function that we can use to start an in-app purchase flow for a particular product. It returns an instance of the PurchaseResult enum defining three cases: success, pending, and userCancelled.
@MainActor final class Store: ObservableObject {
// ...
@Published private(set) var activeTransactions: Set<StoreKit.Transaction> = []
func purchase(_ product: Product) async throws {
let result = try await product.purchase()
switch result {
case .success(let verificationResult):
if let transaction = try? verificationResult.payloadValue {
activeTransactions.insert(transaction)
await transaction.finish()
}
case .userCancelled:
break
case .pending:
break
@unknown default:
break
}
}
}
Whenever the purchase result is in the success state, it provides an associated value of type Transaction defining the successful transaction. StoreKit wraps the transaction in the VerificationResult type allowing us to validate that transaction is correctly signed and comes from the App Store.
The VerificationResult type used by StoreKit 2 to verify that the data is valid and signed by the App Store. It provides us the payloadValue calculated property that we can use to unwrap the signed data or throw an error if the data is not correctly signed.
As soon as you retrieve the transaction, you should unlock the feature user purchased and call the finish function on the particular transaction. Remember, you should always finish the transaction only after unlocking the purchased feature.
struct ContentView: View {
@StateObject private var store = Store()
var body: some View {
VStack {
Text("Purchased items: \(store.activeTransactions.count)")
if store.products.isEmpty {
ProgressView()
} else {
if store.activeTransactions.isEmpty {
ForEach(store.products, id: \.id) { product in
Button {
Task {
try await store.purchase(product)
}
} label: {
VStack {
Text(verbatim: product.displayName)
.font(.headline)
Text(verbatim: product.displayPrice)
}
}
.buttonStyle(.borderedProminent)
}
}
}
}
.task {
await store.fetchProducts()
}
}
}
The purchase becomes pending whenever the ask to buy is enabled. In this case, the transaction arrives later, only after approval by the parent. You should observe the Transaction.updates stream to handle this kind of transaction. We must start monitoring this stream as soon as the app launches to never miss a transaction.
@MainActor final class Store: ObservableObject {
@Published private(set) var activeTransactions: Set<StoreKit.Transaction> = []
private var updates: Task<Void, Never>?
// ...
init() {
updates = Task {
for await update in StoreKit.Transaction.updates {
if let transaction = try? update.payloadValue {
await fetchActiveTransactions()
await transaction.finish()
}
}
}
}
deinit {
updates?.cancel()
}
}
StoreKit 2 provides an easy way to fetch all active subscriptions and purchased products. The currentEntitlements property on Transaction type lists all the active subscriptions and not refunded products.
@MainActor final class Store: ObservableObject {
@Published private(set) var activeTransactions: Set<StoreKit.Transaction> = []
// ...
func fetchActiveTransactions() async {
var activeTransactions: Set<StoreKit.Transaction> = []
for await entitlement in StoreKit.Transaction.currentEntitlements {
if let transaction = try? entitlement.payloadValue {
activeTransactions.insert(transaction)
}
}
self.activeTransactions = activeTransactions
}
}
We can use the currentEntitlements property to fetch all the active purchases on every app launch or more often. By actively monitoring the currentEntitlements property we eliminate need for restoring purchases because the currentEntitlements always contains the latest list of active subscriptions and non-consumable purchases even if they purchased on another device.
@main
struct MyApp: App {
@Environment(\.scenePhase) private var scenePhase
@StateObject private var store = Store()
var body: some Scene {
WindowGroup {
ContentView()
.environmentObject(store)
.task(id: scenePhase) {
if scenePhase == .active {
await store.fetchActiveTransactions()
}
}
}
}
}
Today we started the series of posts about StoreKit 2. As you can see, it is really easy to use and it handle a bunch of use-cases out of the box for you. I hope you enjoy the post. Feel free to follow me on Twitter and ask your questions related to this post. Thanks for reading, and see you next week!