This is a drop-in replacement for Apple's Reachability class. It is ARC-compatible, and it uses the new GCD methods to notify of network interface changes.

In addition to the standard NSNotification, it supports the use of blocks for when the network becomes reachable and unreachable.

Finally, you can specify whether a WWAN connection is considered "reachable".

Once you have added the .h/m files to your project, simply:

• Go to the Project->TARGETS->Build Phases->Link Binary With Libraries.
• Press the plus in the lower left of the list.
• Add SystemConfiguration.framework.

Boom, you're done.

This sample uses blocks to notify when the interface state has changed. The blocks will be called on a BACKGROUND THREAD, so you need to dispatch UI updates onto the main thread.

// Allocate a reachability object
Reachability* reach = [Reachability reachabilityWithHostname:@"www.google.com"];

// Set the blocks
reach.reachableBlock = ^(Reachability*reach)
{
	// keep in mind this is called on a background thread
	// and if you are updating the UI it needs to happen
	// on the main thread, like this:
	
	dispatch_async(dispatch_get_main_queue(), ^{
	  NSLog(@"REACHABLE!");
	});
};

reach.unreachableBlock = ^(Reachability*reach)
{
	NSLog(@"UNREACHABLE!");
};

// Start the notifier, which will cause the reachability object to retain itself!
[reach startNotifier];

This sample will use NSNotifications to notify when the interface has changed. They will be delivered on the MAIN THREAD, so you can do UI updates from within the function.

In addition, it asks the Reachability object to consider the WWAN (3G/EDGE/CDMA) as a non-reachable connection (you might use this if you are writing a video streaming app, for example, to save the user's data plan).

// Allocate a reachability object
Reachability* reach = [Reachability reachabilityWithHostname:@"www.google.com"];

// Tell the reachability that we DON'T want to be reachable on 3G/EDGE/CDMA
reach.reachableOnWWAN = NO;

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

[reach startNotifier];

Head over to Projects using Reachability and add your project for "Maximum Wins!".