扩展UIDevice来监测网络连接

《The iPhone Developer's Cookbook》

没什么好说的，直接上代码：

1、UIDevice+Reachability.h：

#import <UIKit/UIKit.h>
@interface UIDevice (Reachability)
+ (BOOL) networkAvailable;
+ (BOOL) activeWLAN;
+ (BOOL) activeWWAN;
@end

 2、UIDevice+Reachability.m：

#import <SystemConfiguration/SystemConfiguration.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <net/if.h>
#include <ifaddrs.h>
#import "UIDevice-Reachability.h"

@implementation UIDevice (Reachability)
SCNetworkConnectionFlags connectionFlags;

+ (NSString *) localWiFiIPAddress
{
	BOOL success;
	struct ifaddrs * addrs;
	const struct ifaddrs * cursor;
	
	success = getifaddrs(&addrs) == 0;
	if (success) {
		cursor = addrs;
		while (cursor != NULL) {
			// the second test keeps from picking up the loopback address
			if (cursor->ifa_addr->sa_family == AF_INET && (cursor->ifa_flags & IFF_LOOPBACK) == 0) 
			{
				NSString *name = [NSString stringWithUTF8String:cursor->ifa_name];
				if ([name isEqualToString:@"en0"])  // Wi-Fi adapter
					return [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)cursor->ifa_addr)->sin_addr)];
			}
			cursor = cursor->ifa_next;
		}
		freeifaddrs(addrs);
	}
	return nil;
}

#pragma mark Checking Connections

+ (void) pingReachabilityInternal
{
	BOOL ignoresAdHocWiFi = NO;
	struct sockaddr_in ipAddress;
	bzero(&ipAddress, sizeof(ipAddress));
	ipAddress.sin_len = sizeof(ipAddress);
	ipAddress.sin_family = AF_INET;
	ipAddress.sin_addr.s_addr = htonl(ignoresAdHocWiFi ? INADDR_ANY : IN_LINKLOCALNETNUM);
    
    // Recover reachability flags
    SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(kCFAllocatorDefault, (struct sockaddr *)&ipAddress);    
    BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &connectionFlags);
    CFRelease(defaultRouteReachability);
	if (!didRetrieveFlags) 
        printf("Error. Could not recover network reachability flags\n");
}

+ (BOOL) networkAvailable
{
	[self pingReachabilityInternal];
	BOOL isReachable = ((connectionFlags & kSCNetworkFlagsReachable) != 0);
    BOOL needsConnection = ((connectionFlags & kSCNetworkFlagsConnectionRequired) != 0);
    return (isReachable && !needsConnection) ? YES : NO;
}

+ (BOOL) activeWWAN
{
	if (![self networkAvailable]) return NO;
	return ((connectionFlags & kSCNetworkReachabilityFlagsIsWWAN) != 0);
}

+ (BOOL) activeWLAN
{
	return ([UIDevice localWiFiIPAddress] != nil);
}
@end