1.AFNetworking 检测网络状态
    dispatch_async(dispatch_get_global_queue(0,0), ^{
    //如果要检测网络状态的变化,必须用检测管理器的单例的startMonitoring
    [[AFNetworkReachabilityManager sharedManager] startMonitoring];
    __block BOOL network =  network ;
    __block BOOL change =  change ;
    change = NO;
    network = NO;
    // 检测网络连接的单例,网络变化时的回调方法
    [[AFNetworkReachabilityManager sharedManager] setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status)
    {
    switch (status) {
    case AFNetworkReachabilityStatusNotReachable:
    {//无网络

    }
    break;
    case AFNetworkReachabilityStatusReachableViaWiFi:
    {//WiFi网络

    }
    break;
    case AFNetworkReachabilityStatusReachableViaWWAN:
    {//无线网络

    }
    break;
    default:
    break;
    }
    }];
    });