Detecting Network Connectivity Changes using Reachability, NSNotification and Network Link Conditioner in Swift

Question

From iOS 12 you simply use NWPathMonitor which is a line of code (example).

For historic purposes:

---

I'm trying to integrate network connectivity detection into my app, however it seems that somewhere along the line I have made a mistake as my network changes are not being detected/printed out into the console.

As mentioned in the post, I'm currently using these following classes and tools for the job:

1. Reachability {.h, .m}
2. NSNotificationCenter
3. Network Link Conditioner

Code

In the AppDelegate.Swift, I've set up the NSNotificationCenter to detect changes:

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
// ... 
// A: Checks if the device is connected to the internet

    var defaultCenter: Void = NSNotificationCenter().addObserver(self, selector:"checkForReachability", name: kReachabilityChangedNotification, object: nil)

}

In the same class AppDelegate, I've also created this function to be triggered whenever there is a change:

func checkForReachability () {

    var networkReachability = Reachability.reachabilityForInternetConnection()
    networkReachability.startNotifier()

    var remoteHostStatus = networkReachability.currentReachabilityStatus()
    if (remoteHostStatus.value == NotReachable.value) {
        println("Not Reachable")
    } else if (remoteHostStatus.value == ReachableViaWiFi.value) {
        println("Reachable via Wifi")
    } else {
        println("Reachable")
    }
}

However, when using the Network Link Conditioner to manipulate and simulate changes in conditions, I haven't been able to see any of those changes reflected in the console. Any help would be swell!

Solution 1

You must create a Reachability object before you can receive notifications from it. Also, be sure to call the startNotifier() method on the Reachability object you create. This would be an example of how to do so inside of your application delegate:

class AppDelegate: UIResponder, UIApplicationDelegate
{
    private var reachability:Reachability!;

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: NSDictionary?) -> Bool
    {
        NSNotificationCenter.defaultCenter().addObserver(self, selector:"checkForReachability:", name: kReachabilityChangedNotification, object: nil);

        self.reachability = Reachability.reachabilityForInternetConnection();
        self.reachability.startNotifier();
    }

    @objc func checkForReachability(notification:NSNotification)
    {
        // Remove the next two lines of code. You cannot instantiate the object
        // you want to receive notifications from inside of the notification
        // handler that is meant for the notifications it emits.

        //var networkReachability = Reachability.reachabilityForInternetConnection()
        //networkReachability.startNotifier()

        let networkReachability = notification.object as Reachability;
        var remoteHostStatus = networkReachability.currentReachabilityStatus()

        if (remoteHostStatus.value == NotReachable.value)
        {
            println("Not Reachable")
        }
        else if (remoteHostStatus.value == ReachableViaWiFi.value)
        {
            println("Reachable via Wifi")
        }
        else
        {
            println("Reachable")
        }
    }
}

I recommend you take a look at the documentation for NSNotificationCenter and NSNotification. That way you'll be more familiar with how to work with notifications next time something like this comes up.

Swift 3

NotificationCenter.default.addObserver(self, selector:Selector(("checkForReachability:")), name: NSNotification.Name.reachabilityChanged, object: nil)
let reachability: Reachability = Reachability.forInternetConnection()
reachability.startNotifier()

Solution 2

Updated for Swift 4 / Swift 5 according @Hardik.T

1. Import Reachability.swift file from https://github.com/ashleymills/Reachability.swift/archive/master.zip in your XCode project

2. Create a new Swift class : ConnectionManager.swift

class ConnectionManager {

static let sharedInstance = ConnectionManager()
private var reachability : Reachability!

func observeReachability(){
    self.reachability = Reachability()
    NotificationCenter.default.addObserver(self, selector:#selector(self.reachabilityChanged), name: NSNotification.Name.reachabilityChanged, object: nil)
    do {
        try self.reachability.startNotifier()
    }
    catch(let error) {
        print("Error occured while starting reachability notifications : \(error.localizedDescription)")
    }
}

@objc func reachabilityChanged(note: Notification) {
    let reachability = note.object as! Reachability
    switch reachability.connection {
    case .cellular:
        print("Network available via Cellular Data.")
        break
    case .wifi:
        print("Network available via WiFi.")
        break
    case .none:
        print("Network is not available.")
        break
    case .unavailable:
        print("Network is  unavailable.")
        break
    }
  }
}

3. Use it in your AppDelegate file :

func application(_ application: UIApplication,didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    ConnectionManager.sharedInstance.observeReachability()
    return true
}

Solution 3

Instead of polluting the AppDelegate.swift with observer callbacks I would recommend adding observers only into the relevant view controllers.

AppDelegate.swift

import ReachabilitySwift


@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate
{
    var reachability: Reachability?


    func application( _ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]? ) -> Bool
    {
       self.reachability = Reachability()

       do
       {
          try reachability?.startNotifier()
       }
       catch
       {
          print( "ERROR: Could not start reachability notifier." )
       }

       return true
    }


    class func sharedAppDelegate() -> AppDelegate?
    {
        return UIApplication.shared.delegate as? AppDelegate
    }


    // Remaining functions
}

Example of a ViewController:

class ExampleVC: UIViewController
{
    override func viewDidLoad()
    {
        // Add reachability observer
        if let reachability = AppDelegate.sharedAppDelegate()?.reachability
        {
            NotificationCenter.default.addObserver( self, selector: #selector( self.reachabilityChanged ),name: ReachabilityChangedNotification, object: reachability )
        }
    }


    @objc private func reachabilityChanged( notification: NSNotification )
    {
        guard let reachability = notification.object as? Reachability else
        {
            return
        }

        if reachability.isReachable
        {
            if reachability.isReachableViaWiFi
            {
                print("Reachable via WiFi")
            }
            else
            {
                print("Reachable via Cellular")
            }
        }
        else
        {
            print("Network not reachable")
        }
    }
}

Solution 4

Based on this open source solution Wrapped to class

Swift 5

import Foundation

final class ReachabilityHandler {

  private var reachability: Reachability? = Reachability()

  // MARK: - LifeCycle

  init() {
    configure()
  }

  deinit {
    NotificationCenter.default.removeObserver(self)
    reachability?.stopNotifier()
  }

  // MARK: - Private

  private func configure() {
    NotificationCenter.default.addObserver(self,
                                           selector: #selector(ReachabilityHandler.checkForReachability(notification:)),
                                           name: Notification.Name.reachabilityChanged,
                                           object: nil)
    try? reachability?.startNotifier()

  }

  @objc private func checkForReachability(notification: NSNotification) {
    let networkReachability = notification.object as? Reachability
    if let remoteHostStatus = networkReachability?.connection {
      switch remoteHostStatus {
        case .none:

        case .wifi,
             .cellular:

      }
    }
  }
}

In AppDelegate

class AppDelegate: UIResponder, UIApplicationDelegate {

  private var rechabilityObserver: ReachabilityHandler?

  var window: UIWindow?

  // MARK: - LifeCycle

  func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    rechabilityObserver = ReachabilityHandler()

    return true
  }
}

Solution 5

Upadated for swift 2.1 & XCode 7:

try this third party Highly Rated Reachablity Class

 func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: NSDictionary?) -> Bool
    {
 // Allocate a reachability object
        self.reach = Reachability.reachabilityForInternetConnection()

        // Tell the reachability that we DON'T want to be reachable on 3G/EDGE/CDMA
        self.reach!.reachableOnWWAN = false

        // Here we set up a NSNotification observer. The Reachability that caused the notification
        // is passed in the object parameter
        NSNotificationCenter.defaultCenter().addObserver(self,
            selector: "reachabilityChanged:",
            name: kReachabilityChangedNotification,
            object: nil)

        self.reach!.startNotifier()

return true
}

//Reachbality Notification Response

    func reachabilityChanged(notification: NSNotification) {
        if self.reach!.isReachableViaWiFi() || self.reach!.isReachableViaWWAN() {
            print("Service avalaible!!!")
        } else {
            print("No service avalaible!!!")

            AppHelper.showALertWithTag(0, title: constants.AppName.rawValue, message: "Please Check Your Internet Connection!", delegate: self, cancelButtonTitle: "OK", otherButtonTitle: nil)
        }
    }

View more solutions

Comments

[iamktothed]

Thanks, I've changed it. However, I'm still unable to detect network changes via printing to the console.

[A. R. Younce]

Try setting a breakpoint in checkForReachability() to see if it is getting called at all. If so then you'll know your problem has to do with the either that method or the data it receives.

[iamktothed]

I've set the breakpoint and it seems that it's not being called at all.

[iamktothed]

I've implemented the changes and it worked. I had to resort to deploying the iPhone as my Network Link Conditioner wasn't simulating the necessary changes. I'll be sure to dive into the documentation. Thanks!

[iamktothed]

You should consider using a swift statement as it ensures that the exhaustive list of values are being considered. Other than that some, subjectively consider it easier to read, understand and maintain.

[EPage_Ed]

Very true about using Swift switch statement. In my case I just cared if it was reachable or not. However I replicated Younce's code with the fixes for the purposes of the post.

[user2695433]

Hi can you please show example how to pass a NSNotification to checkForReachability method to show a notification to UILabel in a ViewController

[DàChún]

do we need call stopNotifier in AppDelegate?

[A. R. Younce]

@User9527 Probably, but the exact delegate method will depend on how you're using it.

[IgniteCoders]

-1! When you want to check for internet connection changed. You don't know in which view the user is. so you need to check in whole app.

[arauter]

I am checking the whole app. However, only the view controllers interested in an internet connection change, listen to the internet notification.

[Khushboo Dhote]

I am using this method. first time when I a going offline reachabilityChanged() getting called. But again if I am getting connected it is not getting called for any event. Please Help

[Dima G]

Shouldn't we also call "NotificationCenter.default.removeObserver" when the view is not in use any more?

[jayant rawat]

Just a question...how to notify a view controller about network changes ?

[Apple_Magic]

@KhushbooDhote U don't need it now but still posting answer to help any needy...Simulator works in weird way and calling notifier only once...to get notify for each internet connection change debug on real device