NFCViewController.swift

import UIKit
// Step 1: Import CoreNFC library
import CoreNFC 

class ViewController: UIViewController {
  // Step 2: Hold a reference to the NFCNDEFReaderSession object as long as the ViewController stays alive.
  var nfcSession: NFCNDEFReaderSession? 
  
  @IBAction func scanNFCDemoAction(_ sender: Any) {
    startNFC(alertMessage: "Please scan a NFC tag.")
  }
  
  func startNFC(alertMessage: String) {
    // Step 3: Check whether the current device can support NFC tag reading.
     if !NFCNDEFReaderSession.readingAvailable {
      showAlert()
      return
    }
    
    /*
    Step 4: Initialize NFCNDEFReaderSession object with parameter
    invalidateAfterFirstRead:
         true: NFCNDEFReaderSession will be automatically invalidated after the didDetectNDEFs() callback get fired and the blue-tick completion animation is finished. 
                 Any manual invalidation of NFCNDEFReaderSession within didDetectNDEFs() callback will be IGNORED.
         false: NFCNDEFReaderSession will be manually invalidated by developer.
                Thus, it is possible to scan multiple NFC tags at the same time.
    */
    nfcSession = NFCNDEFReaderSession.init(delegate: self, queue: nil, invalidateAfterFirstRead: true)
    
    // Step 5: alert message is the string shown below the scan logo. The max number of line is 3.
    // It is not possible to use an attributed string at the alertMessage property. 
    nfcSession?.alertMessage = alertMessage
    
    // Step 6: To show the NFC reader dialog by beginning the NFC session
    nfcSession?.begin()
  }
}