Any Reachability Experts out there?

Question

My App was working perfectly well until I incorporated the Reachability .h and .m files to it to check for internet connectivity. While for the most part everything still runs perfectly well (all web pages load correctly, and when I purposefully turn-off my Airport to test things, Reachability catches it gracefully) - I do now get inexplicable crashes at odd times, with the dreaded "Exc-Bad-Access" error... I ran Instruments and found the Zombie - see screen-grab:

Looking at the "RefCt" column, you can see it reaches 15 - and I've seen it go higher than 20! In the "Responsible Caller" column (far right), I see all sorts of methods that I don't recognize - and who's call I certainly didn't initiate -- I'm assuming they're called by the system internally during run-time?

Either way, I followed Apple's Reachability code & instructions very carefully, as well as the tips from this very highly-ranked stackoverflow thread: How to check for an active Internet connection on iOS or OSX?

But I'm still getting these inexplicable crashes.

Can anyone offer any advice?

Here's the code:

#import "Reachability.h"


-(void) viewWillAppear:(BOOL)animated
{
   // check for internet connection
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(checkNetworkStatus:) name:kReachabilityChangedNotification object:nil];

internetReachable = [[Reachability reachabilityForInternetConnection] retain];
[internetReachable startNotifier];

// check if a pathway to a random host exists
hostReachable = [[Reachability reachabilityWithHostName: @"www.apple.com"] retain];
[hostReachable startNotifier];

// now patiently wait for the notification
}



-(void) viewDidLoad {

    url = [NSURL URLWithString: @"http://www.google.com"];
    NSURLRequest *req = [NSURLRequest requestWithURL: url];
    [webPageView loadRequest:req];
    [super viewDidLoad];
}



-(void) checkNetworkStatus:(NSNotification *)notice
{
        // called after network status changes

    NetworkStatus internetStatus = [internetReachable currentReachabilityStatus];

    switch (internetStatus) 
    {
        case NotReachable:
        {
            [self displayMessageWithTitle:@"ERROR"
                               andMessage:@"Unable To Connect to Internet"
                              andOKButton:@"OK"];
            [self dismissModalViewControllerAnimated:YES];
            break;

        }
        case ReachableViaWiFi:
        {
            NSLog(@"The internet is working via WIFI.");

            break;

        }
        case ReachableViaWWAN:
        {
            NSLog(@"The internet is working via WWAN.");

            break;

        }
    }

    NetworkStatus hostStatus = [hostReachable currentReachabilityStatus];
    switch (hostStatus)
    {
        case NotReachable:
        {
            // NSLog(@"A gateway to the host server is down.");

            [self displayMessageWithTitle:@"ERROR"
                               andMessage:@"Host Not Reachable"
                              andOKButton:@"OK"];
            [self dismissModalViewControllerAnimated:YES];
            break;

        }

        case ReachableViaWiFi:
        {
            NSLog(@"A gateway to the host server is working via WIFI.");

            break;

        }

        case ReachableViaWWAN:
        {
            NSLog(@"A gateway to the host server is working via WWAN.");

            break;

        }
    }
}



- (void)webViewDidStartLoad:(UIWebView *)webView {
    [activityIndicator startAnimating];
}


- (void)webViewDidFinishLoad:(UIWebView *)webView {
    [activityIndicator stopAnimating];
}


// Since this ViewController is presented Modally, this method removes it 
// via a button click:
-(IBAction) dismissWebTixView:(id)sender {
    [self dismissModalViewControllerAnimated:YES];
}




-(void) viewWillDisappear:(BOOL)animated {
    NSLog(@"In webForTix's 'viewWillDisappear' method....");
    [[NSNotificationCenter defaultCenter] removeObserver:self
name:kReachabilityChangedNotification
                                              object:nil];
}


// Was told it might be good to put "removeObserver" here and not in viewWillDisappear
// well neither worked - the App still crashes....
- (void)dealloc
{
    //NSLog(@"In webForTix's dealloc method....");
//    [[NSNotificationCenter defaultCenter] removeObserver:self
//                                                        name:kReachabilityChangedNotification
//                                                  object:nil];
NSLog(@"In webForTix's dealloc method - removedObserver...");
[super dealloc];

}

Answer 1

You have to carefully balance calls to addObserver and removeObserver.

If you add an observer for a notification in vieWillAppear, you need to remove it in viewWillDisappear.

If you add observer twice, you will get called twice for the same notification, and have to call removeObserver twice in order to get rid of both notifications.

I didn't see any obvious memory management problems. It looks like all the code you posted is creating auto-released objects, which should be fine.