ios – 持续检测互联网连接

- (void)applicationDidBecomeActive:(UIApplication *)application {

    Reachability *networkReachability = [Reachability reachabilityForInternetConnection];
    NetworkStatus networkStatus = [networkReachability currentReachabilityStatus];
    if (networkStatus == NotReachable) {
        [Settings hideSpinner];
         //Show no internet connectivity dialog.
    } else {
    }
}

但问题是它不是在不断检查互联网连接.
它仅在应用程序变为活动状态时进行检查.如何在整个应用程序生命周期内持续检查互联网连接,并在互联网自动关闭时发出警告？

1)[[NSNotificationCenter defaultCenter] addObserver：self selector：@selector(reachabilityChanged