This is a singleton class to detect internet connection. It can be customized to check if internet connection is over WiFi or cellular. Example of use : if ([ALData checkInternetConnection]) NSLog(@"Internet available"); else NSLog(@"Internet unavailable");

ALData.h

//
//  ALData.h
//  AL
//
//  Created by Andrea Lufino on 09/05/12.
//  Copyright 2012 Andrea Lufino. All rights reserved.

#import <Foundation/Foundation.h>
#import <SystemConfiguration/SystemConfiguration.h>
#import <sys/socket.h>
#import <netinet/in.h>
#import "ALMacros.h"

/*!
 A singleton class useful to check the internet connection. Needs the SystemConfiguration framework.
 */
@interface ALData : NSObject

/*!
 ----------------------------
 /// @name Internet check
 -----------------------------
 */

/*!
 This method check the internet connection.
 @return A BOOL value based on the presence or less of the internet connection. YES if internet connection is available, NO if it isn't
 */
+ (BOOL)checkInternetConnection;

@end

ALData.m

//
//  ALData.m
//  AL
//
//  Created by Andrea Lufino on 09/05/12.
//  Copyright 2012 Andrea Lufino. All rights reserved.

#import "ALData.h"

@implementation ALData

#pragma mark - Singleton methods

+ (ALData *)shared {

	static ALData *_shared;
	if(!_shared) {
		static dispatch_once_t oncePredicate;
		dispatch_once(&oncePredicate, ^ {
			_shared = [[super allocWithZone:nil] init];
		});
	}
	
	return _shared;
}

+ (id)allocWithZone:(NSZone *)zone { return [self shared]; }
- (id)copyWithZone:(NSZone *)zone { return self; }
#if (!__has_feature(objc_arc))
- (id)retain { return self; }
- (unsigned)retainCount { return UINT_MAX; }
- (void)release {}
- (id)autorelease { return self; }
#endif

#pragma mark - Custom methods

+ (BOOL)checkInternetConnection {
    SINGLETON
    struct sockaddr_in zeroAddress;
    bzero(&zeroAddress, sizeof(zeroAddress));
    zeroAddress.sin_len = sizeof(zeroAddress);
    zeroAddress.sin_family = AF_INET;
    
    SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithAddress(kCFAllocatorDefault, (const struct sockaddr*)&zeroAddress);
    if(reachability != NULL) {
        //NetworkStatus retVal = NotReachable;
        SCNetworkReachabilityFlags flags;
        if (SCNetworkReachabilityGetFlags(reachability, &flags)) {
            if ((flags & kSCNetworkReachabilityFlagsReachable) == 0)
            {
                // if target host is not reachable
                return NO;
            }
            if ((flags & kSCNetworkReachabilityFlagsConnectionRequired) == 0)
            {
                // if target host is reachable and no connection is required
                //  then we'll assume (for now) that your on Wi-Fi
                return YES;
            }
            if ((((flags & kSCNetworkReachabilityFlagsConnectionOnDemand ) != 0) ||
                 (flags & kSCNetworkReachabilityFlagsConnectionOnTraffic) != 0))
            {
                // ... and the connection is on-demand (or on-traffic) if the
                //     calling application is using the CFSocketStream or higher APIs
                
                if ((flags & kSCNetworkReachabilityFlagsInterventionRequired) == 0)
                {
                    // ... and no [user] intervention is needed
                    return YES;
                }
            }
            if ((flags & kSCNetworkReachabilityFlagsIsWWAN) == kSCNetworkReachabilityFlagsIsWWAN)
            {
                // ... but WWAN connections are OK if the calling application
                //     is using the CFNetwork (CFSocketStream?) APIs.
                return YES;
            }
        }
    }
    
    return NO;
}

@end