typedef enum : NSInteger {

  NotReachable = 0, //无连接
  ReachableViaWiFi, //使用3G/GPRS网络
  ReachableViaWWAN //使用WiFi网络

} NetworkStatus;

// AppDelegate.m


@interface AppDelegate ()

@property (nonatomic, strong) Reachability *reachability;

@end

// 程序启动器，启动网络监视
- (void)applicationDidFinishLaunching:(UIApplication *)application {

  // 设置网络检测的站点
    NSString *remoteHostName = @"www.apple.com";
  self.reachability = [Reachability reachabilityWithHostName:remoteHostName];
  // 设置网络状态变化时的通知函数
  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:)
                       name:@"kNetworkReachabilityChangedNotification" object:nil];
  [self updateStatus];
}


- (void)reachabilityStatusChange:(NSNotification *)notification
{
  Reachability* curReach = [notification object];
  NSParameterAssert([curReach isKindOfClass:[Reachability class]]);
  [self updateInterfaceWithReachability:curReach];
}

- (void)updateInterfaceWithReachability:(Reachability *)reachability
{
  if (reachability == _reachability)
  {
    NetworkStatus netStatus = [reachability currentReachabilityStatus];
    switch (netStatus)
    {
      case NotReachable:   {
        NSLog(@"没有网络！");
        break;
      }
      case ReachableViaWWAN: {
        NSLog(@"4G/3G");
        break;
      }
      case ReachableViaWiFi: {
        NSLog(@"WiFi");
        break;
      }
    }
  }
}


- (void)dealloc
{
   [_reachability stopNotifier];
  [[NSNotificationCenter defaultCenter] removeObserver:self name:kReachabilityChangedNotification object:nil];
} 

//使用AFN框架来检测网络状态的改变
-(void)AFNReachability
{
  //1.创建网络监听管理者
  AFNetworkReachabilityManager *manager = [AFNetworkReachabilityManager sharedManager];

  //2.监听网络状态的改变
  /*
   AFNetworkReachabilityStatusUnknown     = 未知
   AFNetworkReachabilityStatusNotReachable   = 没有网络
   AFNetworkReachabilityStatusReachableViaWWAN = 3G
   AFNetworkReachabilityStatusReachableViaWiFi = WIFI
   */
  [manager setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status) {
    switch (status) {
      case AFNetworkReachabilityStatusUnknown:
        NSLog(@"未知");
        break;
      case AFNetworkReachabilityStatusNotReachable:
        NSLog(@"没有网络");
        break;
      case AFNetworkReachabilityStatusReachableViaWWAN:
        NSLog(@"3G");
        break;
      case AFNetworkReachabilityStatusReachableViaWiFi:
        NSLog(@"WIFI");
        break;

      default:
        break;
    }
  }];

  //3.开始监听
  [manager startMonitoring];
}