前言

今天翻阅苹果的API文档，发现多了一个框架Core NFC，看了下才看见是iOS11.0新添加的框架，这里我们就一起来看一下框架Core NFC。感兴趣的看下面几篇文章。
1. Core NFC框架详细解析 （一） —— 基本概览（一）
2. Core NFC框架详细解析 （二） —— CoreNFC使用简单示例（一）

源码

1. Swift

首先看下工程组织结构

下面就是源码了

1. NFCUtility.swift

import Foundation
import CoreNFC

typealias NFCReadingCompletion = (Result<NFCNDEFMessage?, Error>) -> Void
typealias LocationReadingCompletion = (Result<Location, Error>) -> Void

enum NFCError: LocalizedError {
  case unavailable
  case invalidated(message: String)
  case invalidPayloadSize

  var errorDescription: String? {
    switch self {
    case .unavailable:
      return "NFC Reader Not Available"
    case let .invalidated(message):
      return message
    case .invalidPayloadSize:
      return "NDEF payload size exceeds the tag limit"
    }
  }
}

class NFCUtility: NSObject {
  enum NFCAction {
    case readLocation
    case setupLocation(locationName: String)
    case addVisitor(visitorName: String)

    var alertMessage: String {
      switch self {
      case .readLocation:
        return "Place tag near iPhone to read the location."
      case .setupLocation(let locationName):
        return "Place tag near iPhone to setup \(locationName)"
      case .addVisitor(let visitorName):
        return "Place tag near iPhone to add \(visitorName)"
      }
    }
  }

  private static let shared = NFCUtility()
  private var action: NFCAction = .readLocation

  // 1
  private var session: NFCNDEFReaderSession?
  private var completion: LocationReadingCompletion?

  // 2
  static func performAction(
    _ action: NFCAction,
    completion: LocationReadingCompletion? = nil
  ) {
    // 3
    guard NFCNDEFReaderSession.readingAvailable else {
      completion?(.failure(NFCError.unavailable))
      print("NFC is not available on this device")
      return
    }

    shared.action = action
    shared.completion = completion
    // 4
    shared.session = NFCNDEFReaderSession(
      delegate: shared.self,
      queue: nil,
      invalidateAfterFirstRead: false)
    // 5
    shared.session?.alertMessage = action.alertMessage
    // 6
    shared.session?.begin()
  }
}

// MARK: - NFC NDEF Reader Session Delegate
extension NFCUtility: NFCNDEFReaderSessionDelegate {
  func readerSession(
    _ session: NFCNDEFReaderSession,
    didDetectNDEFs messages: [NFCNDEFMessage]
  ) {
    // Not used
  }

  private func handleError(_ error: Error) {
    session?.alertMessage = error.localizedDescription
    session?.invalidate()
  }

  func readerSession(
    _ session: NFCNDEFReaderSession,
    didInvalidateWithError error: Error
  ) {
    if
      let error = error as? NFCReaderError,
      error.code != .readerSessionInvalidationErrorFirstNDEFTagRead &&
        error.code != .readerSessionInvalidationErrorUserCanceled {
      completion?(.failure(NFCError.invalidated(message: error.localizedDescription)))
    }

    self.session = nil
    completion = nil
  }

  func readerSession(
    _ session: NFCNDEFReaderSession,
    didDetect tags: [NFCNDEFTag]
  ) {
    guard
      let tag = tags.first,
      tags.count == 1
      else {
        session.alertMessage = "There are too many tags present. Remove all and then try again."
        DispatchQueue.global().asyncAfter(deadline: .now() + .milliseconds(500)) {
          session.restartPolling()
        }
        return
    }

    // 1
    session.connect(to: tag) { error in
      if let error = error {
        self.handleError(error)
        return
      }

      // 2
      tag.queryNDEFStatus { status, _, error in
        if let error = error {
          self.handleError(error)
          return
        }

        // 3
        switch (status, self.action) {
        case (.notSupported, _):
          session.alertMessage = "Unsupported tag."
          session.invalidate()
        case (.readOnly, _):
          session.alertMessage = "Unable to write to tag."
          session.invalidate()
        case (.readWrite, .setupLocation(let locationName)):
          self.createLocation(Location(name: locationName), tag: tag)
        case (.readWrite, .readLocation):
          self.read(tag: tag)
        case (.readWrite, .addVisitor(let visitorName)):
          self.addVisitor(Visitor(name: visitorName), tag: tag)
        default:
          return
        }
      }
    }
  }
}

// MARK: - Utilities
extension NFCUtility {
  func readLocation(from tag: NFCNDEFTag) {
    // 1
    tag.readNDEF { message, error in
      if let error = error {
        self.handleError(error)
        return
      }
      // 2
      guard
        let message = message,
        let location = Location(message: message)
        else {
          self.session?.alertMessage = "Could not read tag data."
          self.session?.invalidate()
          return
      }
      self.completion?(.success(location))
      self.session?.alertMessage = "Read tag."
      self.session?.invalidate()
    }
  }

  private func read(
    tag: NFCNDEFTag,
    alertMessage: String = "Tag Read",
    readCompletion: NFCReadingCompletion? = nil
  ) {
    tag.readNDEF { message, error in
      if let error = error {
        self.handleError(error)
        return
      }

      // 1
      if let readCompletion = readCompletion,
        let message = message {
        readCompletion(.success(message))
      } else if let message = message,
        let record = message.records.first,
        let location = try? JSONDecoder()
          .decode(Location.self, from: record.payload) {
        // 2
        self.completion?(.success(location))
        self.session?.alertMessage = alertMessage
        self.session?.invalidate()
      } else {
        self.session?.alertMessage = "Could not decode tag data."
        self.session?.invalidate()
      }
    }
  }

  private func createLocation(_ location: Location, tag: NFCNDEFTag) {
    read(tag: tag) { _ in
      self.updateLocation(location, tag: tag)
    }
  }

  private func updateLocation(
    _ location: Location,
    withVisitor visitor: Visitor? = nil,
    tag: NFCNDEFTag
  ) {
    // 1
    var alertMessage = "Successfully setup location."
    var tempLocation = location

    if let visitor = visitor {
      tempLocation.visitors.append(visitor)
      alertMessage = "Successfully added visitor."
    }

    // 2
    let jsonEncoder = JSONEncoder()
    guard let customData = try? jsonEncoder.encode(tempLocation) else {
      self.handleError(NFCError.invalidated(message: "Bad data"))
      return
    }

    // 3
    let payload = NFCNDEFPayload(
      format: .unknown,
      type: Data(),
      identifier: Data(),
      payload: customData)
    // 4
    let message = NFCNDEFMessage(records: [payload])

    tag.queryNDEFStatus { _, capacity, _ in
      // 1
      guard message.length <= capacity else {
        self.handleError(NFCError.invalidPayloadSize)
        return
      }

      // 2
      tag.writeNDEF(message) { error in
        if let error = error {
          self.handleError(error)
          return
        }
        if self.completion != nil {
          self.read(tag: tag, alertMessage: alertMessage)
        }
      }
    }
  }

  private func addVisitor(_ visitor: Visitor, tag: NFCNDEFTag) {
    read(tag: tag) { message in
      guard
        let message = try? message.get(),
        let record = message.records.first,
        let location = try? JSONDecoder()
          .decode(Location.self, from: record.payload)
        else {
          return
      }

      self.updateLocation(location, withVisitor: visitor, tag: tag)
    }
  }
}

2. LocationModel.swift

import CoreNFC

struct Location: Codable {
  let name: String
  var visitors: [Visitor]

  init(name: String) {
    self.name = name
    visitors = []
  }

  init?(message: NFCNDEFMessage) {
    guard
      let locationRecord = message.records.first,
      let locationName = locationRecord.wellKnownTypeTextPayload().0
      else {
        return nil
    }

    name = locationName
    visitors = []
  }
}

struct Visitor: Codable, Hashable {
  let name: String

  init(name: String) {
    self.name = name
  }
}

3. AppView.swift

import SwiftUI

struct AppView: View {
  var body: some View {
    TabView {
      VisitorView()
        .tabItem {
          VStack {
            Image(systemName: "magnifyingglass")
            Text("Visitors")
          }
        }
      AdminView()
        .tabItem {
          VStack {
            Image(systemName: "lock")
            Text("Admin")
          }
        }
    }
    .accentColor(Color("rw-green"))
  }
}

struct AppView_Previews: PreviewProvider {
  static var previews: some View {
    Group {
      AppView()
    }
  }
}

4. VisitorView.swift

import SwiftUI

struct VisitorView: View {
  @State private var visitorName = ""
  @State private var locationModel: Location?

  // swiftlint:disable multiple_closures_with_trailing_closure multiline_arguments
  private var visitorSection: some View {
    Section(header: Text("Visitor Information")) {
      TextField("Enter Your Name", text: $visitorName)
        .textContentType(.name)
        .autocapitalization(.words)

      Button(action: {
        NFCUtility.performAction(.addVisitor(visitorName: self.visitorName)) { location in
          self.locationModel = try? location.get()
          self.visitorName = ""
        }
      }) {
        Text("Add To Tag…")
      }
      .disabled(visitorName.isEmpty)
    }
  }

  private var scanSection: some View {
    Section {
      Button(action: {
        NFCUtility.performAction(.readLocation) { location in
          self.locationModel = try? location.get()
        }
      }) {
        Text("Scan Location Tag…")
      }
    }
  }
  // swiftlint:enable multiple_closures_with_trailing_closure multiline_arguments

  private var scannedSection: some View {
    locationModel.map { location in
      Section(
        header: Text("Location: \(location.name)"),
        footer: Text("Visitors: \(location.visitors.count)")) {
          ForEach(location.visitors, id: \.self) { visitor in
            Text(visitor.name)
          }
      }
    }
  }

  var body: some View {
    NavigationView {
      Form {
        visitorSection
        scanSection
        scannedSection
      }
      .navigationBarTitle("Visitors")
    }
    .navigationViewStyle(StackNavigationViewStyle())
  }
}

struct VisitorView_Previews: PreviewProvider {
  static var previews: some View {
    VisitorView()
  }
}

5. AdminView.swift

import SwiftUI

struct AdminView: View {
  @State private var locationName = ""

  var body: some View {
    NavigationView {
      Form {
        Section(
          header: Text("Location Setup"),
          footer: Text("This will clear all visitor data from tag.")
            .fontWeight(.bold)
        ) {
          TextField("Enter Location Name", text: $locationName)
            .autocapitalization(.words)
          // swiftlint:disable multiple_closures_with_trailing_closure multiline_arguments
          Button(action: {
            NFCUtility.performAction(.setupLocation(locationName: self.locationName)) { _ in
              self.locationName = ""
            }
          }) {
            Text("Save Location…")
          }
          .disabled(locationName.isEmpty)
        }
        // swiftlint:enable multiple_closures_with_trailing_closure multiline_arguments
      }
      .navigationBarTitle("Administration")
    }
    .navigationViewStyle(StackNavigationViewStyle())
  }
}

struct AdminView_Previews: PreviewProvider {
  static var previews: some View {
    AdminView()
  }
}

后记

本篇主要讲述了CoreNFC使用简单示例，感兴趣的给个赞或者关注~~~