如何在iOS 13中检查网络不可用？

Reachability *reachability = [Reachability reachabilityForInternetConnection];

NetworkStatus networkStatus = [reachability currentReachabilityStatus];
if (networkStatus == NotReachable) {
    NSLog(@"网络不可用");
} else {
    NSLog(@"网络可用");
}

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

- (void)networkStatusChanged:(NSNotification *)notification {
    Reachability *reachability = (Reachability *)[notification object];
    NetworkStatus networkStatus = [reachability currentReachabilityStatus];
    if (networkStatus == NotReachable) {
        NSLog(@"网络不可用");
    } else {
        NSLog(@"网络可用");
    }
}