- (BOOL)connectedToNetwork{

    //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

    struct sockaddr_storage zeroAddress;

    bzero(&zeroAddress, sizeof(zeroAddress));
    zeroAddress.ss_len = sizeof(zeroAddress);
    zeroAddress.ss_family = AF_INET;

    // Recover reachability flags
    SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(NULL, (struct sockaddr *)&zeroAddress);
    SCNetworkReachabilityFlags flags;

    //获得连接的标志
    BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags);
    CFRelease(defaultRouteReachability);

    //如果不能获取连接标志，则不能连接网络，直接返回
    if (!didRetrieveFlags)
    {
        return NO;
    }
    //根据获得的连接标志进行判断

    BOOL isReachable = flags & kSCNetworkFlagsReachable;
    BOOL needsConnection = flags & kSCNetworkFlagsConnectionRequired;
    return (isReachable&&!needsConnection) ? YES : NO;
}