當應用程序在 iOS Swift 后台時，如何通過 MQTT 客戶端框架發布或發送消息

Question

我正在開發一個應用程序，通過 MQTT 客戶端框架每 15 分鍾發送一次當前用戶位置。 當應用程序在前台時，它工作正常，但當應用程序在后台時，不會調用 MQTT 委托函數“messageDelivered”

我們想使用 MQTT 客戶端框架在 iOS swift 中在后台發布消息。

import UIKit
import MQTTClient

class MainViewController: UIViewController {
    
    let MQTT_HOST = "next.nanolink.com" // or IP address e.g. "192.168.0.194"
    //let MQTT_HOST = "tnclicks.free.beeceptor.com" // or IP address e.g. "192.168.0.194"
    let MQTT_PORT: UInt32 = 1883
    
    private var transport = MQTTCFSocketTransport()
    fileprivate var session = MQTTSession()
    fileprivate var completion: (()->())?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        
        //notification observer
        NotificationCenter.default.addObserver(self, selector: #selector(onDidReceiveData(_:)), name: .didReceiveData, object: nil)
        

        //MQTT
        self.session?.delegate = self
        self.transport.host = MQTT_HOST
        self.transport.port = MQTT_PORT
        session?.transport = transport

        
        updateUI(for: self.session?.status ?? .created)
        session?.connect() { error in
            print("connection completed with status \(String(describing: error?.localizedDescription))")
            if error != nil {
                self.updateUI(for: self.session?.status ?? .created)
            } else {
                self.updateUI(for: self.session?.status ?? .error)
            }
        }
        
    }
    
    private func subscribe() {
        self.session?.subscribe(toTopic: "test/message", at: .exactlyOnce) { error, result in
            print("subscribe result error \(String(describing: error)) result \(result!)")
        }
    }
    
    private func updateUI(for clientStatus: MQTTSessionStatus) {
        DispatchQueue.main.async {
            switch clientStatus {
                case .connected:
                    print("Connected")
                    self.publishMessage("on", onTopic: "test/message")

                case .connecting,
                     .created:
                    print ("Trying to connect...")
                default:
                    print ("Connetion Failed...")
            }
        }
    }
    
    private func publishMessage(_ message: String, onTopic topic: String)
    {
        session?.publishData(message.data(using: .utf8, allowLossyConversion: false), onTopic: topic, retain: false, qos: .exactlyOnce)
    }
    
    @objc func onDidReceiveData(_ notification:Notification) {
        print("check return")
        
        guard session?.status == .connected else {
            self.updateUI(for: self.session?.status ?? .error)
            return
        }
        
        let obj  =  notification.object! as! NSMutableDictionary
        
        print(notification.object!)
        let notificationLatitude = obj.value(forKey: "latitude")!
        let notificationLongitude = obj.value(forKey: "longitude")!
        
        //let notificationLongitude = notification.object

//        print(" Saved latitude:", latitude!)
//        print(" Saved longitude:", longitude!)
        
        print(" notification latitude:", notificationLatitude)
        print(" notification longitude:", notificationLongitude)
        
        guard session?.status == .connected else {
            return
        }
        publishMessage("on", onTopic: "test/message")

    }
   
}


extension MainViewController: MQTTSessionManagerDelegate, MQTTSessionDelegate {

    func newMessage(_ session: MQTTSession!, data: Data!, onTopic topic: String!, qos: MQTTQosLevel, retained: Bool, mid: UInt32) {
        if let msg = String(data: data, encoding: .utf8) {
            print("topic \(topic!), msg \(msg)")
        }
    }

    func messageDelivered(_ session: MQTTSession, msgID msgId: UInt16) {
        print("delivered")
        DispatchQueue.main.async {
            self.completion?()
        }
    }
}


extension Notification.Name {
    static let didReceiveData = Notification.Name("didReceiveData")
}

Answer 1

我們已經在后台實現了更新位置，因此使用更新位置更新您的代碼以在后台發送消息。

import UIKit
import CoreLocation
@UIApplicationMain

class AppDelegate: UIResponder, UIApplicationDelegate,CLLocationManagerDelegate {
var window: UIWindow?
var locationManager = CLLocationManager()
var backgroundUpdateTask: UIBackgroundTaskIdentifier!
var bgtimer = Timer()
var latitude: Double = 0.0
var longitude: Double = 0.0
var current_time = NSDate().timeIntervalSince1970
var timer = Timer()
var f = 0
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    self.doBackgroundTask()
    return true
}


func applicationWillResignActive(_ application: UIApplication) {
}

func applicationWillEnterForeground(_ application: UIApplication) {
    print("Entering foreBackground")
}

func applicationDidBecomeActive(_ application: UIApplication) {
}

func applicationWillTerminate(_ application: UIApplication) {
}

func applicationDidEnterBackground(_ application: UIApplication) {
    print("Entering Background")
   // self.doBackgroundTask()
}

func doBackgroundTask() {

    DispatchQueue.main.async {

        self.beginBackgroundUpdateTask()

        self.StartupdateLocation()


        self.bgtimer = Timer.scheduledTimer(timeInterval:-1, target: self, selector: #selector(AppDelegate.bgtimer(_:)), userInfo: nil, repeats: true)
        RunLoop.current.add(self.bgtimer, forMode: RunLoopMode.defaultRunLoopMode)
        RunLoop.current.run()

        self.endBackgroundUpdateTask()

    }
}

func beginBackgroundUpdateTask() {
    self.backgroundUpdateTask = UIApplication.shared.beginBackgroundTask(expirationHandler: {
        self.endBackgroundUpdateTask()
    })
}

func endBackgroundUpdateTask() {
    UIApplication.shared.endBackgroundTask(self.backgroundUpdateTask)
    self.backgroundUpdateTask = UIBackgroundTaskInvalid
}

func StartupdateLocation() {
    locationManager.delegate = self
    locationManager.desiredAccuracy = kCLLocationAccuracyBest
    locationManager.distanceFilter = kCLDistanceFilterNone
    locationManager.requestAlwaysAuthorization()
    locationManager.allowsBackgroundLocationUpdates = true
    locationManager.pausesLocationUpdatesAutomatically = false
    locationManager.startUpdatingLocation()
}

func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
    print("Error while requesting new coordinates")
}

func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {

    let locValue:CLLocationCoordinate2D = manager.location!.coordinate

    self.latitude = locValue.latitude
    self.longitude = locValue.longitude
    f+=1
    print("New Coordinates: \(f) ")
    print(self.latitude)
    print(self.longitude)
}

@objc func bgtimer(_ timer:Timer!){
    sleep(2)
  /*  if UIApplication.shared.applicationState == .active {
         timer.invalidate()
    }*/
    self.updateLocation()
}

func updateLocation() {
    self.locationManager.startUpdatingLocation()
    self.locationManager.stopUpdatingLocation()
}}