有网时自动刷新数据

这需要检测网络状态，只需要有网和没网两种状态即可(处理多种状态时可以在下边的通知方法netChanged中添加)。这里用到的是第三方框架Reachability

地址是这里
在viewController的viewDidLoad中添加监控网络的方法

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor lightGrayColor];
    [self monitorNetworkState];
}

/** 监控网络状态 */
-(void)monitorNetworkState{
    //kReachabilityChangedNotification是Reachability中的通知名称
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(netChanged:) name:kReachabilityChangedNotification object:nil];
    Reachability *net = [Reachability reachabilityForInternetConnection];
    [net startNotifier];
}

-(void)netChanged:(NSNotification *)notification{
    Reachability *reachability = (Reachability *)notification.object;
    NetworkStatus status = reachability.currentReachabilityStatus;
    if (status != NotReachable) {
        UIAlertView *alert = [[UIAlertView alloc]initWithTitle:nil message:@"有网了" delegate:nil cancelButtonTitle:@"取消" otherButtonTitles:nil, nil];
        [alert show];
    }
}

上边的代码即可满足需求