//网络检测
    //    1.创建网络监听者管理者对象
    AFNetworkReachabilityManager *manager = [AFNetworkReachabilityManager sharedManager];
    //    -设置网络监听
    [manager setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status) {
        switch (status) {
            case AFNetworkReachabilityStatusUnknown:
                NSLog(@"未识别的网络");
                break;
                
            case AFNetworkReachabilityStatusNotReachable:
                NSLog(@"不可达的网络(未连接)");
                break;
                
            case AFNetworkReachabilityStatusReachableViaWWAN:
                NSLog(@"2G,3G,4G...的网络");
                break;
                
            case AFNetworkReachabilityStatusReachableViaWiFi:
                NSLog(@"wifi的网络");
                break;
            default:
                break;
        }
    }];
    //    3.开始监听
    [manager startMonitoring];

  pod ‘AFNetworking‘, ‘~> 3.1.0‘