FirstViewController.swift

//
//  FirstViewController.swift
//  AnotherBT
//
//  Created by Paul Wilkinson on 15/7/17.
//  Copyright © 2017 Paul Wilkinson. All rights reserved.
//

import UIKit
import CoreBluetooth
class FirstViewController: UIViewController {
    
    var central: CBCentralManager!
    var connectedPeripheral: CBPeripheral?
    @IBOutlet weak var scanSwitch: UISwitch!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        self.central = CBCentralManager(delegate: self, queue: nil)
        
        self.scanSwitch.isOn = false
        self.scanSwitch.isEnabled = false
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    @IBAction func scanSwitched(_ sender: UISwitch) {
        if sender.isOn {
            self.central.scanForPeripherals(withServices: [CBUUID(string:"dc495108-adce-4915-942d-bfc19cea923f")], options: nil)
        } else {
            self.central.stopScan()
        }
    }


}

extension FirstViewController: CBCentralManagerDelegate {
    
    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        if central.state == .poweredOn {
            self.scanSwitch.isEnabled = true
        } else {
            self.scanSwitch.isEnabled = false
        }
    }
    
    func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
        print("Discovered peripheral \(peripheral)")
        self.connectedPeripheral = peripheral
        central.connect(peripheral, options: nil)
    }
    
    func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
        print("Connected peripheral \(peripheral)")
        peripheral.discoverServices(nil)
        peripheral.delegate = self
    }
    
    
}

extension FirstViewController: CBPeripheralDelegate {
    func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
        print(error.debugDescription)
        if service.characteristics != nil {
            for characteristic in service.characteristics! {
                if characteristic.uuid == CBUUID(string: "A4389A32-90D2-402F-A3DF-47996E123DC1") {
                    print("characteristic found")
                    peripheral.readValue(for: characteristic)
                }
            }
        }
    }
    
    func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
        if peripheral.services != nil {
            for service in peripheral.services! {
                if service.uuid == CBUUID(string: "dc495108-adce-4915-942d-bfc19cea923f") {
                    peripheral.discoverCharacteristics(nil, for: service)
                }
            }
        }
    }
}

SecondViewController.swift

//
//  SecondViewController.swift
//  AnotherBT
//
//  Created by Paul Wilkinson on 15/7/17.
//  Copyright © 2017 Paul Wilkinson. All rights reserved.
//

import UIKit
import CoreBluetooth

class SecondViewController: UIViewController {
    
    
    @IBOutlet weak var advertiseSwitch: UISwitch!
    
    var peripheralManager: CBPeripheralManager!
    var service: CBMutableService!
    var characteristic: CBMutableCharacteristic!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        
        self.peripheralManager = CBPeripheralManager(delegate: self, queue: nil)
        self.advertiseSwitch.isOn = false
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    func setupBT() {
        self.service = CBMutableService(type: CBUUID(string:"dc495108-adce-4915-942d-bfc19cea923f"), primary: true)
        self.characteristic = CBMutableCharacteristic(type: CBUUID(string: "A4389A32-90D2-402F-A3DF-47996E123DC1"), properties: [.write, .read], value: nil, permissions: [.writeable, .readable])
        self.service.characteristics = [characteristic]
        self.peripheralManager.add(self.service)
    }
    
    @IBAction func advertiseSwitched(_ sender: UISwitch) {
        if sender.isOn {
            self.peripheralManager.startAdvertising([CBAdvertisementDataServiceUUIDsKey:[self.service.uuid]])
        } else {
            self.peripheralManager.stopAdvertising()
        }
    }
    
}

extension SecondViewController: CBPeripheralManagerDelegate {
    
    func peripheralManagerDidUpdateState(_ peripheral: CBPeripheralManager) {
        switch peripheral.state {
        case .poweredOn:
            self.advertiseSwitch.isEnabled = true
            if (self.service == nil) {
                self.setupBT()
            }
        default:
            self.advertiseSwitch.isEnabled = false
        }
    }
}