【初心者向け】買い切り（買い切り解除）iOSアプリの作り方：StoreKit2で非消耗型IAPを実装→テスト→審査まで

import StoreKit
import SwiftUI

@MainActor
final class PurchaseStore: ObservableObject {
    // あなたの Product ID（App Store Connect で設定したもの）
    static let proProductID = "com.example.app.pro"

    @Published var product: Product?
    @Published var isProUnlocked: Bool = false
    @Published var lastErrorMessage: String?

    private var updatesTask: Task<Void, Never>?

    init() {
        // 1) 起動直後から Transaction.updates を監視（取りこぼし防止）
        updatesTask = Task { await observeTransactionUpdates() }

        // 2) 起動時に entitlement を復元（再インストール/機種変更でも反映）
        Task { await refreshEntitlements() }

        // 3) 商品情報を取得
        Task { await loadProduct() }
    }

    deinit { updatesTask?.cancel() }

    func loadProduct() async {
        do {
            let products = try await Product.products(for: [Self.proProductID])
            self.product = products.first
        } catch {
            lastErrorMessage = "商品情報の取得に失敗: \(error.localizedDescription)"
        }
    }

    func buyPro() async {
        guard let product else { return }
        do {
            let result = try await product.purchase()
            switch result {
            case .success(let verification):
                let transaction = try checkVerified(verification)
                await transaction.finish()   // finish は必須
                await refreshEntitlements()
            case .userCancelled:
                break
            case .pending:
                // 承認待ち（Ask to Buy等）
                break
            @unknown default:
                break
            }
        } catch {
            lastErrorMessage = "購入に失敗: \(error.localizedDescription)"
        }
    }

    /// 「復元」ボタンに紐付ける（非消耗型は復元導線が必要）
    func restore() async {
        do {
            try await AppStore.sync()
            await refreshEntitlements()
        } catch {
            lastErrorMessage = "復元に失敗: \(error.localizedDescription)"
        }
    }

    /// 現在の権利（entitlements）から Pro 解放を判断
    func refreshEntitlements() async {
        var unlocked = false
        for await result in Transaction.currentEntitlements {
            if let transaction = try? checkVerified(result),
               transaction.productID == Self.proProductID {
                unlocked = true
            }
        }
        isProUnlocked = unlocked
    }

    /// アプリ外で発生した取引も含め、更新を監視
    private func observeTransactionUpdates() async {
        for await result in Transaction.updates {
            if let transaction = try? checkVerified(result),
               transaction.productID == Self.proProductID {
                await transaction.finish()
                await refreshEntitlements()
            }
        }
    }

    private func checkVerified<T>(_ result: VerificationResult<T>) throws -> T {
        switch result {
        case .verified(let safe): return safe
        case .unverified: throw StoreError.failedVerification
        }
    }

    enum StoreError: Error { case failedVerification }
}

struct PaywallView: View {
    @StateObject private var store = PurchaseStore()

    var body: some View {
        VStack(spacing: 16) {
            Text(store.isProUnlocked ? "✅ Pro 解放済み" : "🔒 Pro を解放する")
                .font(.title3)

            if let product = store.product {
                Text("買い切り: \(product.displayPrice)")
                Button("購入する") {
                    Task { await store.buyPro() }
                }
                .buttonStyle(.borderedProminent)

                Button("購入を復元する") {
                    Task { await store.restore() }
                }
                .buttonStyle(.bordered)
            } else {
                ProgressView("商品情報を取得中…")
            }

            if let msg = store.lastErrorMessage {
                Text(msg).foregroundStyle(.red)
            }
        }
        .padding()
    }
}