这个类可以用来检测用户是否连接到internet，只有一个方法，返回YES或NO。功能类似Reachability。

类的头文件Connection.h

复制代码
//
// Connection.h
//
#import <Foundation/Foundation.h>
#import <SystemConfiguration/SystemConfiguration.h>
#import <netinet/in.h>
#import <arpa/inet.h>
#import <netdb.h>

@interface Connection : NSObject {
}
+ (BOOL) isConnected;
@end
复制代码

类的实现文件Connection.m

复制代码
//
// Connection.m
//
@implementation Connection

+ (BOOL) isConnected {
    // 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) {
        NSLog(@"Error,Could not recover network reachability flags");
         return NO;
    }
    BOOL  isReachable = flags & kSCNetworkFlagsReachable;
    BOOL  needsConnection = flags  &  kSCNetworkFlagsConnectionRequired;
    BOOL  nonWiFi = flags  &  kSCNetworkReachabilityFlagsTransientConnection;

     NSURL  *testURL = [NSURL  URLWithString:@"http://www.google.com/"];
    NSURLRequest  *testRequest = [NSURLRequest  requestWithURL:testURL  cachePolicy:NSURLRequestReloadIgnoringLocalCacheData  timeoutInterval:20.0];
    NSURLConnection  *testConnection = [[NSURLConnection  alloc] initWithRequest:testRequest  delegate:self] autorelease];
    return ((isReachable && !needsConnection) || nonWiFi) ? (testConnection ? YES : NO) : NO;
}

@end
复制代码

最后别忘了添加必要的frameworks : SystemConfiguration and libz.1.1.3.dylib

示例代码：

if ([Connection isConnected]) {......}
else {......}