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

-(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
}
 
Use a simple library to do it:

https://github.com/tonymillion/Reachability (ARC and GCD Compatible Reachability)

OR… Do it yourself:

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 (you can get those here)

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

  -(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.

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