AFN检測网络情况

[[AFNetworkReachabilityManager sharedManager] setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status) {
    NSLog(@"Reachability: %@", AFStringFromNetworkReachabilityStatus(status));
}];

-startMonitoring
-stopMonitoring

答：

The -startMonitoring method of AFNetworking is used to make your
AFNetworkReachabilityManager start monitoring the network connection. If you do not call
-startMonitoring, your setReachabilityStatusChangeBlock will
never be called (regardless of where you put it) since AFNetworking isn‘t monitoring your connection.

As you probably assumed, -stopMonitoring does the exact opposite of
-startMonitoring - it stops the manager from checking network connectivity. I normally don‘t use this method in my apps, but if your app doesn‘t need a network connection for a certain part of it, feel free to call it (just make sure you start
monitoring the network again when you need to).

The setReachabilityStatusChangeBlock is called whenever the network status changes. You can put this wherever you want to make changes if/when the network changes. An example of this would be putting it in your app delegate and sending out a
NSNotification when the network status changes so that any view controller observing the notification can react appropriately.

You can also manually check to see if the network is online (as long as
-startMonitoring was called and AFNetworking is monitoring your network) using something like this:

if ([[AFNetworkReachabilityManager sharedManager] isReachable]) {
    NSLog(@"Online");
}

You can read more on AFNetworking‘s official documentation on GitHub.