DFly7/core-nfc

CoreNFC

Read and write NFC tags on iPhone using the CoreNFC framework. Covers NDEF reader sessions, tag reader sessions, NDEF message construction, entitlements, and background tag reading. Targets Swift 6.3 / iOS 26+.

Contents

• Setup
• NDEF Reader Session
• Tag Reader Session
• Writing NDEF Messages
• NDEF Payload Types
• Background Tag Reading
• Common Mistakes
• Review Checklist
• References

Setup

Project Configuration

1. Add the Near Field Communication Tag Reading capability in Xcode
2. Add NFCReaderUsageDescription to Info.plist with a user-facing reason string
3. Add the com.apple.developer.nfc.readersession.formats entitlement with the tag types your app reads (e.g., NDEF, TAG)
4. For ISO 7816 tags, add supported application identifiers to com.apple.developer.nfc.readersession.iso7816.select-identifiers in Info.plist

Device Requirements

NFC reading requires iPhone 7 or later. Always check for reader session availability before presenting NFC UI.

import CoreNFC

guard NFCNDEFReaderSession.readingAvailable else {
    // Device does not support NFC or feature is restricted
    showUnsupportedMessage()
    return
}

Key Types

| Type | Role | |---|---| | NFCNDEFReaderSession | Scans for NDEF-formatted tags | | NFCTagReaderSession | Scans for ISO7816, ISO15693, FeliCa, MIFARE tags | | NFCNDEFMessage | Collection of NDEF payload records | | NFCNDEFPayload | Single record within an NDEF message | | NFCNDEFTag | Protocol for interacting with an NDEF-capable tag |

NDEF Reader Session

Use NFCNDEFReaderSession to read NDEF-formatted data from tags. This is the simplest path for reading standard tag content like URLs, text, and MIME data.

import CoreNFC

final class NDEFReader: NSObject, NFCNDEFReaderSessionDelegate {
    private var session: NFCNDEFReaderSession?

    func beginScanning() {
        guard NFCNDEFReaderSession.readingAvailable else { return }

        session = NFCNDEFReaderSession(
            delegate: self,
            queue: nil,
            invalidateAfterFirstRead: false
        )
        session?.alertMessage = "Hold your iPhone near an NFC tag."
        session?.begin()
    }

    // MARK: - NFCNDEFReaderSessionDelegate

    func readerSessionDidBecomeActive(_ session: NFCNDEFReaderSession) {
        // Session is scanning
    }

    func readerSession(
        _ session: NFCNDEFReaderSession,
        didDetectNDEFs messages: [NFCNDEFMessage]
    ) {
        for message in messages {
            for record in message.records {
                processRecord(record)
            }
        }
    }

    func readerSession(
        _ session: NFCNDEFReaderSession,
        didInvalidateWithError error: Error
    ) {
        let nfcError = error as? NFCReaderError
        if nfcError?.code != .readerSessionInvalidationErrorFirstNDEFTagRead,
           nfcError?.code != .readerSessionInvalidationErrorUserCanceled {
            print("Session invalidated: \(error.localizedDescription)")
        }
        self.session = nil
    }
}

Reading with Tag Connection

For read-write operations, use the tag-detection delegate method to connect to individual tags:

func readerSession(
    _ session: NFCNDEFReaderSession,
    didDetect tags: [any NFCNDEFTag]
) {
    guard let tag = tags.first else {
        session.restartPolling()
        return
    }

    session.connect(to: tag) { error in
        if let error {
            session.invalidate(errorMessage: "Connection failed: \(error)")
            return
        }

        tag.queryNDEFStatus { status, capacity, error in
            guard error == nil else {
                session.invalidate(errorMessage: "Query failed.")
                return
            }

            switch status {
            case .notSupported:
                session.invalidate(errorMessage: "Tag is not NDEF compliant.")
            case .readOnly:
                tag.readNDEF { message, error in
                    if let message {
                        self.processMessage(message)
                    }
                    session.invalidate()
                }
            case .readWrite:
                tag.readNDEF { message, error in
                    if let message {
                        self.processMessage(message)
                    }
                    session.alertMessage = "Tag read successfully."
                    session.invalidate()
                }
            @unknown default:
                session.invalidate()
            }
        }
    }
}

Tag Reader Session

Use NFCTagReaderSession when you need direct access to the native tag protocol (ISO 7816, ISO 15693, FeliCa, or MIFARE).

final class TagReader: NSObject, NFCTagReaderSessionDelegate {
    private var session: NFCTagReaderSession?

    func beginScanning() {
        session = NFCTagReaderSession(
            pollingOption: [.iso14443, .iso15693],
            delegate: self,
            queue: nil
        )
        session?.alertMessage = "Hold your iPhone near a tag."
        session?.begin()
    }

    func tagReaderSessionDidBecomeActive(
        _ session: NFCTagReaderSession
    ) { }

    func tagReaderSession(
        _ session: NFCTagReaderSession,
        didDetect tags: [NFCTag]
    ) {
        guard let tag = tags.first else { return }

        session.connect(to: tag) { error in
            guard error == nil else {
                session.invalidate(
                    errorMessage: "Connection failed."
                )
                return
            }

            switch tag {
            case .iso7816(let iso7816Tag):
                self.readISO7816(tag: iso7816Tag, session: session)
            case .miFare(let miFareTag):
                self.readMiFare(tag: miFareTag, session: session)
            case .iso15693(let iso15693Tag):
                self.readISO15693(tag: iso15693Tag, session: session)
            case .feliCa(let feliCaTag):
                self.readFeliCa(tag: feliCaTag, session: session)
            @unknown default:
                session.invalidate(errorMessage: "Unsupported tag type.")
            }
        }
    }

    func tagReaderSession(
        _ session: NFCTagReaderSession,
        didInvalidateWithError error: Error
    ) {
        self.session = nil
    }
}

Writing NDEF Messages

Write NDEF data to a connected tag. Always check readWrite status first.

func writeToTag(
    tag: any NFCNDEFTag,
    session: NFCNDEFReaderSession,
    url: URL
) {
    tag.queryNDEFStatus { status, capacity, error in
        guard status == .readWrite else {
            session.invalidate(errorMessage: "Tag is read-only.")
            return
        }

        guard let payload = NFCNDEFPayload.wellKnownTypeURIPayload(
            url: url
        ) else {
            session.invalidate(errorMessage: "Invalid URL.")
            return
        }

        let message = NFCNDEFMessage(records: [payload])

        tag.writeNDEF(message) { error in
            if let error {
                session.invalidate(
                    errorMessage: "Write failed: \(error.localizedDescription)"
                )
            } else {
                session.alertMessage = "Tag written successfully."
                session.invalidate()
            }
        }
    }
}

NDEF Payload Types

Creating Common Payloads

// URL payload
let urlPayload = NFCNDEFPayload.wellKnownTypeURIPayload(
    url: URL(string: "https://example.com")!
)

// Text payload
let textPayload = NFCNDEFPayload.wellKnownTypeTextPayload(
    string: "Hello NFC",
    locale: Locale(identifier: "en")
)

// Custom payload
let customPayload = NFCNDEFPayload(
    format: .nfcExternal,
    type: "com.example:mytype".data(using: .utf8)!,
    identifier: Data(),
    payload: "custom-data".data(using: .utf8)!
)

Parsing Payload Content

func processRecord(_ record: NFCNDEFPayload) {
    switch record.typeNameFormat {
    case .nfcWellKnown:
        if let url = record.wellKnownTypeURIPayload() {
            print("URL: \(url)")
        } else if let (text, locale) = record.wellKnownTypeTextPayload() {
            print("Text (\(locale)): \(text)")
        }
    case .absoluteURI:
        if let uri = String(data: record.payload, encoding: .utf8) {
            print("Absolute URI: \(uri)")
        }
    case .media:
        let mimeType = String(data: record.type, encoding: .utf8) ?? ""
        print("MIME type: \(mimeType), size: \(record.payload.count)")
    case .nfcExternal:
        let type = String(data: record.type, encoding: .utf8) ?? ""
        print("External type: \(type)")
    case .empty, .unknown, .unchanged:
        break
    @unknown default:
        break
    }
}

Background Tag Reading

On iPhone XS and later, iOS can read NFC tags in the background without opening your app. To opt in:

1. Add associated domains or universal links that match the URL on your tags
2. Register your app for the tag's NDEF content type
3. Include your app's bundle ID in the tag's NDEF record

When a user taps a compatible tag, iOS displays a notification that opens your app. Handle the tag data via NSUserActivity:

func scene(
    _ scene: UIScene,
    continue userActivity: NSUserActivity
) {
    guard userActivity.activityType ==
        NSUserActivityTypeBrowsingWeb else { return }

    if let message = userActivity.ndefMessagePayload {
        for record in message.records {
            processRecord(record)
        }
    }
}

Common Mistakes

DON'T: Forget the NFC entitlement

Without the com.apple.developer.nfc.readersession.formats entitlement, session creation crashes at runtime.

// WRONG -- entitlement not added, crashes
let session = NFCNDEFReaderSession(
    delegate: self, queue: nil, invalidateAfterFirstRead: true
)

// CORRECT -- add entitlement in Signing & Capabilities first
// Then the same code works:
let session = NFCNDEFReaderSession(
    delegate: self, queue: nil, invalidateAfterFirstRead: true
)

DON'T: Skip the readingAvailable check

Attempting to create an NFC session on an unsupported device (iPad, iPod touch, or iPhone 6s and earlier) crashes.

// WRONG
func scan() {
    let session = NFCNDEFReaderSession(
        delegate: self, queue: nil, invalidateAfterFirstRead: true
    )
    session.begin()
}

// CORRECT
func scan() {
    guard NFCNDEFReaderSession.readingAvailable else {
        showUnsupportedAlert()
        return
    }
    let session = NFCNDEFReaderSession(
        delegate: self, queue: nil, invalidateAfterFirstRead: true
    )
    session.begin()
}

DON'T: Ignore session invalidation errors

The session invalidates for multiple reasons. Distinguishing user cancellation from real errors prevents false error alerts.

// WRONG -- shows error when user cancels
func readerSession(
    _ session: NFCNDEFReaderSession,
    didInvalidateWithError error: Error
) {
    showAlert("NFC Error: \(error.localizedDescription)")
}

// CORRECT -- filter expected invalidation reasons
func readerSession(
    _ session: NFCNDEFReaderSession,
    didInvalidateWithError error: Error
) {
    let nfcError = error as? NFCReaderError
    switch nfcError?.code {
    case .readerSessionInvalidationErrorUserCanceled,
         .readerSessionInvalidationErrorFirstNDEFTagRead:
        break  // Normal termination
    default:
        showAlert("NFC Error: \(error.localizedDescription)")
    }
    self.session = nil
}

DON'T: Hold a strong reference to a stale session

Once a session is invalidated, it cannot be restarted. Nil out your reference and create a new session for the next scan.

// WRONG -- reusing invalidated session
func scanAgain() {
    session?.begin()  // Does nothing, session is dead
}

// CORRECT -- create a new session
func scanAgain() {
    session = NFCNDEFReaderSession(
        delegate: self, queue: nil, invalidateAfterFirstRead: false
    )
    session?.begin()
}

DON'T: Write without checking tag status

Writing to a read-only tag silently fails or produces confusing errors.

// WRONG -- writes without checking status
tag.writeNDEF(message) { error in
    // May fail on read-only tags
}

// CORRECT -- check status first
tag.queryNDEFStatus { status, capacity, error in
    guard status == .readWrite else {
        session.invalidate(errorMessage: "Tag is read-only.")
        return
    }
    tag.writeNDEF(message) { error in
        // Handle result
    }
}

Review Checklist

• [ ] NFC capability added in Signing & Capabilities
• [ ] NFCReaderUsageDescription set in Info.plist
• [ ] com.apple.developer.nfc.readersession.formats entitlement configured with correct tag types
• [ ] NFCNDEFReaderSession.readingAvailable checked before creating sessions
• [ ] Session delegate set before calling begin()
• [ ] Session reference set to nil after invalidation
• [ ] didInvalidateWithError distinguishes user cancellation from actual errors
• [ ] NDEF status queried before write operations
• [ ] Tag capacity checked before writing large messages
• [ ] ISO 7816 application identifiers listed in Info.plist if using NFCTagReaderSession
• [ ] Background tag reading configured with associated domains if needed
• [ ] Only one reader session active at a time

References

• Extended patterns (ISO 7816 commands, multi-tag scanning, NDEF locking): references/nfc-patterns.md
• Core NFC framework
• NFCNDEFReaderSession
• NFCTagReaderSession
• NFCNDEFMessage
• NFCNDEFPayload
• NFCNDEFTag
• NFCNDEFReaderSessionDelegate
• NFCTagReaderSessionDelegate
• Building an NFC Tag-Reader App
• Adding Support for Background Tag Reading
• Near Field Communication Tag Reader Session Formats Entitlement