iOS 判断网络是否连接

 1 //判断网络是否连接
 2 + (BOOL) connectedToNetwork
 3 {
 4     //创建零地址，0.0.0.0的地址表示查询本机的网络连接状态
 5     struct sockaddr_in zeroAddress;            //struct用来向方法中传递复杂的参数(把参数当作对象,这样便于扩展)
 6     bzero(&zeroAddress, sizeof(zeroAddress));
 7     zeroAddress.sin_len = sizeof(zeroAddress);
 8     zeroAddress.sin_family = AF_INET;
 9     
10     // Recover reachability flags
11     SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(NULL, (struct sockaddr *)&zeroAddress);
12     SCNetworkReachabilityFlags flags;
13     //获得连接的标志
14     BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags);
15     CFRelease(defaultRouteReachability);
16     //如果不能获取连接标志，则不能连接网络，直接返回
17     if (!didRetrieveFlags)
18     {
19         return NO;
20     }
21     //根据获得的连接标志进行判断
22     BOOL isReachable = flags & kSCNetworkFlagsReachable;
23     BOOL needsConnection = flags & kSCNetworkFlagsConnectionRequired;
24     BOOL isWWAN = flags & kSCNetworkReachabilityFlagsIsWWAN;
25     return (isReachable && (!needsConnection || isWWAN)) ? YES : NO;
26 }