iOS开发中判断网络连接的操作步骤如下：

1、添加framework，SystemConfiguration.framework；

2、倒入文件：

#import <SystemConfiguration/SystemConfiguration.h>
#include <netdb.h>

 3、判断方法：

- (BOOL) connectedToNetwork {
    // Create zero addy
    struct sockaddr_in zeroAddress;
    bzero(&zeroAddress, sizeof(zeroAddress));
    zeroAddress.sin_len = sizeof(zeroAddress);
    zeroAddress.sin_family = AF_INET;
    
    // Recover reachability flags
    SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(NULL, (struct sockaddr *)&zeroAddress);    
    SCNetworkReachabilityFlags flags;
    BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags);
    CFRelease(defaultRouteReachability);
    if (!didRetrieveFlags) {
        return NO;
    }
    BOOL isReachable = ((flags & kSCNetworkFlagsReachable) != 0);
    BOOL needsConnection = ((flags & kSCNetworkFlagsConnectionRequired) != 0);
    return (isReachable && !needsConnection) ? YES : NO;
}

 来自《The iPhone Developer's Cookbook》

最新版本的SDK下载地址：https://developers.google.com/mobile-ads-sdk/download#downloadios

SDK使用的开发指南地址：https://developers.google.com/mobile-ads-sdk/docs/ios/fundamentals#incorporating

最近要更新项目中的AdMob SDK，本来认为直接替换就可以了，但是却出现了一些错误。产生问题的原因是AdMob提供的SDK升级后，对应的开发指南却没有更新。从一个测试项目来开，按照开发指南添加SDK和相关代码后，错误如下所示：

根据问题详细描述，经过调查需要添加另外的两个库，分别是SdSupport.framework和StoreKit.framework，添加后对项目的重新编译就可以通过了！
 

至此，看似问题已经解决，但是运行时出现了强制退出。出现异常：libc++abi.dylib: terminating with uncaught exception of type NSException

问题解决方法是：在TARGETS－Build Settings－Other Linker Flags属性添加-ObjC属性即可！

运行效果如图：

开发环境：Xcode5.0＋OS X10.8.5

多说一句：出错的原因可能是我们做了什么事情，或我们没做本应该做的事情！上述问题的解决是建立在特定情境中，希望对你有所帮助！：）

《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