iOS: Reachability - startNotifier fails after returning to app

Question

I have Reachability working exactly as suggested as in this thread.

I am using the open source Reachability. However I am not using blocks but notifications, hence the process is pretty similar to the Apple's Reachability code.

The first time I start the app, I run this and it works great.

Reachability *reachability = [reach hostReachability];
[reachability startNotifier];

The reachabilityChanged: event is firing:

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

However once I press the home button and come back to the app, the startNotifier returns internally a NO instead of a YES.

    // Set it as our reachability queue, which will retain the queue
    if(!SCNetworkReachabilitySetDispatchQueue(self.reachabilityRef, self.reachabilitySerialQueue))
    {
#ifdef DEBUG
        NSLog(@"SCNetworkReachabilitySetDispatchQueue() failed: %s", SCErrorString(SCError()));
#endif
      ...
      return NO;

and hence the event above is never fired again.

Unless I am using this wrongly and startNotifier should only be called once in init when reachability is instantiated and never again?

self.hostReachability = [Reachability reachabilityWithHostname:_HOST];

Answer 1

You should only need to call [self.hostReachability startNotifier] once on init/load. Here's a rundown of your basic needs, using notifications rather than the block method on the linked thread:

1. Add the tonymillion/Reachability library to your project.

2. Create property for your Reachability object to make sure it's retained, eg.

   @interface ViewController () {
     NSString *_HOST;
   }
   @property Reachability *hostReachability;
   @end
   

3. Register for change notifications, and start the notifier, eg.

   - (void)viewDidLoad
   {
     [super viewDidLoad];
   
     [[NSNotificationCenter defaultCenter] addObserver:self
                                              selector:@selector(reachabilityChanged:)
                                                  name:kReachabilityChangedNotification
                                                object:nil];
   
     _HOST = @"www.google.com";
     self.hostReachability = [Reachability reachabilityWithHostname:_HOST];
     [self.hostReachability startNotifier];
   }
   
   - (void)viewDidUnload
   {
     [super viewDidUnload];
   
     [[NSNotificationCenter defaultCenter] removeObserver:self];
   }
   

4. Finally, create a reachabilityChanged: method to handle your response to Reachability changes, eg.

   - (void)reachabilityChanged:(NSNotification*)notification
   {
     Reachability *notifier = [notification object];
     NSLog(@"%@", [notifier currentReachabilityString]);
   }
   

Note: If you press the Home button and unload the app, changes in Reachability should fire a notification immediately upon returning to the app.