首先是在AppDelegate.m中设置网络监听

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name:kReachabilityChangedNotification object:nil];

初始化：

_reachability = [Reachability reachabilityForInternetConnection];  [_reachability startNotifier];  [self updateInterfaceWithReachability:_reachability];

实现两个方法：

- (void) reachabilityChanged: (NSNotification* )note;//网络连接改变

- (void) updateInterfaceWithReachability: (Reachability*) curReach;//处理连接改变后的情况

下面是方法的具体实现，可根据情况自行改变：

// 连接改变  - (void) reachabilityChanged: (NSNotification* )note {      Reachability* curReach = [note object];      NSParameterAssert([curReach isKindOfClass: [Reachability class]]);      [self updateInterfaceWithReachability: curReach];  }    //处理连接改变后的情况  - (void) updateInterfaceWithReachability: (Reachability*) curReach {      //对连接改变做出响应的处理动作。      NetworkStatus status = [curReach currentReachabilityStatus];            if (status == NotReachable) {          _isReachable = NO;          //没有连接到网络就弹出提实况          UIAlertView *netAlert = [[UIAlertView alloc] initWithTitle:@"蜂窝移动数据已关闭" message:@"启用蜂窝移动数据或无线局域网来访问数据" delegate:nil cancelButtonTitle:@"确定" otherButtonTitles:nil];          [netAlert show];      } else {          _isReachable = YES;      }  }