How to check for an active Internet Connection on iPhone SDK?

Question

I would like to check to see if I have an Internet connection on the iPhone using the Cocoa Touch libraries.

I came up with a way to do this using an NSUrl. The way I did it seems a bit unreliable (because even Google could one day be down and relying on a 3rd party seems bad) and while I could check to see for a response from some other websites if Google didn't respond, it does seem wasteful and an unnecessary overhead on my application.

- (BOOL) connectedToInternet
{
    NSString *URLString = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://www.google.com"]];
    return ( URLString != NULL ) ? YES : NO;
}

Is what I have done bad? (Not to mention 'stringWithContentsOfURL' is deprecated in 3.0) And if so what is a better way to accomplish this?

Update (Unanswered):

It's been a long time, well the current answer is kind of outdated, so if you post the asynchronous code (using NSNotificationCenter) I will mark it as the new correct answer. I would answer it myself, but that seems that I would have a conflict of interest in marking my own answer as correct :)

Answer 1

The type of check that you propose would not accomplish anything since the connection could be lost immediately after the check or during the subsequent operation. Instead, you should put code that requires an internet connection in separate threads (I recommend using NSOperation and/or NSInvocationOperation for this task). If the data is not received within a certain period of time, inform the user that a connection could not be established.

Answer 2

Apple provides a sample app which does exactly this:

http://developer.apple.com/iphone/library/samplecode/Reachability/index.html

Answer 3

Apple supply sample code to check for different types of network availability. Alternatively there is an example in the iPhone developers cookbook.

Note: Please see @KHG's comment on this answer regarding the use of Apple's reachability code.

Answer 4

I've used the code in this discussion, and it seems to work fine (read the whole thread!).

I haven't tested it exhaustively with every conceivable kind of connection (like ad hoc wifi).

Answer 5

Edit: This used to be the correct answer, but is now outdated as you should subscribe to notifications for reachability instead. This methods checks synchronously:

You can use Apple's Reachability class. It will also allow you to check if WiFi is enabled:

Reachability* reachability = [Reachability sharedReachability];
[reachability setHostName:@"www.example.com"];    // set your host name here
NetworkStatus remoteHostStatus = [reachability remoteHostStatus];

if(remoteHostStatus == NotReachable) { }
else if (remoteHostStatus == ReachableViaWiFiNetwork) { }
else if (remoteHostStatus == ReachableViaCarrierDataNetwork) { }

The Reachability class is not shipped with the SDK, but rather a part of this Apple sample application. Just download it and copy Reachability.h/m to your project. Also, you have to add the SystemConfiguration framework to your project.

Answer 6

Nice topic, a bit old but thanks anyway it helped me. Only the Reachability class has been updated. You can now use:

Reachability* reachability = [Reachability reachabilityWithHostName:@"www.apple.com"];
NetworkStatus remoteHostStatus = [reachability currentReachabilityStatus];

if(remoteHostStatus == NotReachable) { NSLog(@"not reachable");}
else if (remoteHostStatus == ReachableViaWWAN) { NSLog(@"reachable via wwan");}
else if (remoteHostStatus == ReachableViaWiFi) { NSLog(@"reachable via wifi");}

Answer 7

An updated answer:

1) Add SystemConfiguration framework to the project but don't worry about including it anywhere

2) Add Reachability.h and Reachability.m to the project

3) Add @class Reachability; to the .h file of where you are implementing the code

4) Create a couple instances to check in the interface section of the .h file:

    Reachability* internetReachable;
    Reachability* hostReachable;

5) Add a method in the .h for when the network status updates:

    - (void) checkNetworkStatus:(NSNotification *)notice;

6) Add #import "Reachability.h" to the .m file where you are implementing the check

7) In the .m file of where you are implementing the check, you can place this in one of the first methods called (init or viewWillAppear or viewDidLoad etc):

    -(void) viewWillAppear:(BOOL)animated
    {
        // check for internet connection
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(checkNetworkStatus:) name:kReachabilityChangedNotification object:nil];

        internetReachable = [[Reachability reachabilityForInternetConnection] retain];
        [internetReachable startNotifier];

        // check if a pathway to a random host exists
        hostReachable = [[Reachability reachabilityWithHostName: @"www.apple.com"] retain];
        [hostReachable startNotifier];

        // now patiently wait for the notification
    }

8) Set up the method for when the notification gets sent and set whatever checks or call whatever methods you may have set up (in my case, I just set a BOOL)

    - (void) checkNetworkStatus:(NSNotification *)notice
    {
     // called after network status changes

     NetworkStatus internetStatus = [internetReachable currentReachabilityStatus];
     switch (internetStatus)

        {
      case NotReachable:
            {
       NSLog(@"The internet is down.");
       self.internetActive = NO;

                break;

            }
      case ReachableViaWiFi:
            {
       NSLog(@"The internet is working via WIFI.");
       self.internetActive = YES;

                break;

            }
      case ReachableViaWWAN:
            {
       NSLog(@"The internet is working via WWAN.");
       self.internetActive = YES;

                break;

            }
     }

     NetworkStatus hostStatus = [hostReachable currentReachabilityStatus];
     switch (hostStatus)

        {
      case NotReachable:
            {
       NSLog(@"A gateway to the host server is down.");
       self.hostActive = NO;

                break;

            }
      case ReachableViaWiFi:
            {
       NSLog(@"A gateway to the host server is working via WIFI.");
       self.hostActive = YES;

                break;

            }
      case ReachableViaWWAN:
            {
       NSLog(@"A gateway to the host server is working via WWAN.");
       self.hostActive = YES;

                break;

            }
     }
    }

9) In your dealloc or viewWillDisappear or similar method, remove yourself as an observer

    - (void) viewWillDisappear:(BOOL)animated
    {

            [[NSNotificationCenter defaultCenter] removeObserver:self];

    }

Note: There might be an instance using viewWillDisappear where you receive a memory warning and the observer never gets unregistered so you should account for that as well.