SwiftUI App + Core NFC + Swift Concurrency を使って書いた、交通系電子マネーカードの残高読み取りサンプル。 https://twitter.com/treastrain/status/1431356306963587072

ConcurrencyNFCApp.swift

//
//  ConcurrencyNFCApp.swift
//  ConcurrencyNFC
//
//  Created by treastrain on 2021/08/28.
//

import SwiftUI
import CoreNFC

@main
struct ConcurrencyNFCApp: App {
    @ObservedObject var viewModel = ViewModel()
    @State private var balance: String = "¥----"
    
    var body: some Scene {
        WindowGroup {
            NavigationView {
                VStack {
                    Text(balance).font(.largeTitle).padding()
                    Spacer()
                    Button {
                        Task {
                            do {
                                let balance = try await viewModel.scan()
                                self.balance = balance.formatted(.currency(code: "JPY"))
                            } catch NFCReaderError.readerSessionInvalidationErrorUserCanceled {
                                // do nothing
                            } catch { self.balance = error.localizedDescription }
                        }
                    } label: { Text("Scan").font(.title) }
                    .padding()
                }
                .navigationTitle("Concurrency NFC")
            }
        }
    }
}

class ViewModel: NSObject, ObservableObject {
    enum NFCError: Error {
        case readingUnavailable
    }
    
    private var activeContinuation: CheckedContinuation<Int, Error>?
    private var session: NFCTagReaderSession?
    
    func scan() async throws -> Int {
        guard NFCTagReaderSession.readingAvailable else { throw NFCError.readingUnavailable }
        return try await withCheckedThrowingContinuation { continuation in
            activeContinuation = continuation
            session = NFCTagReaderSession(pollingOption: .iso18092, delegate: self)
            session?.alertMessage = "Place the top of your iPhone on the card."
            session?.begin()
        }
    }
}

extension ViewModel: NFCTagReaderSessionDelegate {
    func tagReaderSessionDidBecomeActive(_ session: NFCTagReaderSession) {}
    
    func tagReaderSession(_ session: NFCTagReaderSession, didInvalidateWithError error: Error) {
        activeContinuation?.resume(throwing: error)
        activeContinuation = nil
    }
    
    func tagReaderSession(_ session: NFCTagReaderSession, didDetect tags: [NFCTag]) {
        Task { () -> Void in
            try await session.connect(to: tags.first!)
            guard case .some(.feliCa(let feliCaTag)) = session.connectedTag else {
                return session.invalidate(errorMessage: "The tag is not FeliCa.")
            }
            session.alertMessage = "Scanning..."
            let (status1, status2, blockData) = try await feliCaTag.readWithoutEncryption(serviceCodeList: [Data([0x8B, 0x00])], blockList: [Data([0x80, 0x00])])
            guard status1 == 0, status2 == 0, let data = blockData.first else {
                return session.invalidate(errorMessage: "Status flags indicate an error, or the block data is invalid.")
            }
            session.alertMessage = "Succeeded!"
            session.invalidate()
            activeContinuation?.resume(returning: data.toIntReversed(11, 12))
            activeContinuation = nil
        }
    }
}

extension Data {
    /// https://github.com/treastrain/TRETJapanNFCReader/blob/master/TRETJapanNFCReader/Extensions.swift#L112
    func toIntReversed(_ startIndex: Int, _ endIndex: Int) -> Int {
        var s = 0
        for (n, i) in (startIndex...endIndex).enumerated() {
            s += Int(self[i]) << (n * 8)
        }
        return s
    }
}