iOS UIAlertView提供EXC_BAD_ACCESS

Question

I have searched for awhile and tried many things, but I cannot get this error to go away. I have a table that is refreshed by a pull down method. I also use Apple's Reachability to determine internet connectivity. When I run my application WITH internet, and then while the app is running, shut the internet off, my app crashes trying to display a UIAlertView. Although, when I start my app WITHOUT internet and then turn on internet while the app is running and turn it back off, the app does not crash and everything works as it should. Any help would be greatly appreciated.

The error occurs on the [message show] line.

Edited code:

- (void)loadCallList {

NSURL *theURL = [NSURL URLWithString:@"http://www.wccca.com/PITS/"];

NSURLRequest *theRequest = [NSURLRequest requestWithURL:theURL cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:10.0];
NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];

if (theConnection) {

    NSLog(@"Reachable");

    self.headerHeight = 45.0;

    NSData *data = [[NSData alloc] initWithContentsOfURL:theURL];
    xpathParser = [[TFHpple alloc] initWithHTMLData:data];
    NSArray *elements = [xpathParser searchWithXPathQuery:@"//input[@id='hidXMLID']//@value"];

        if (elements.count >= 1) {

            TFHppleElement *element = [elements objectAtIndex:0];
            TFHppleElement *child = [element.children objectAtIndex:0];
            NSString *idValue = [child content];

            NSString *idwithxml = [idValue stringByAppendingFormat:@".xml"];
            NSString *url = @"http://www.wccca.com/PITS/xml/fire_data_";
            NSString *finalurl = [url stringByAppendingString:idwithxml];

            xmlParser = [[XMLParser alloc] loadXMLByURL:finalurl];

            [callsTableView reloadData];
        }
    }

else {

    NSLog(@"Not Reachable");

    self.headerHeight = 0.0;

    UIAlertView *message = [[UIAlertView alloc] initWithTitle:@"No Internet Connection"
                                                      message:@"Please check your internet connection and pull down to refresh."
                                                     delegate:self
                                            cancelButtonTitle:@"OK"
                                            otherButtonTitles:nil];
    [message show];
    [message release];
}

[pull finishedLoading];
}

Answer 1

You have two problems:

1. You shouldn't be using Reachability to determine whether there is an internet connection. Reachability is only useful to determine when an offline connection comes back online. Really. Making the networking calls is sometimes enough to power up the radios and connect so if you try to pre-check whether there is an internet connection the radios will remain off.

2. The second problem is that no synchronous networking calls can be made on the main thread. This includes Reachability and [NSData dataWithContentsOfURL:xxx]. Make them on a secondary thread using Grand Central Dispatch, NSOperationQueues, NSURLConnections, or NSThreads. Otherwise your application can lock up if the network isn't in good shape and the system watchdog timer will kill your app.

Answer 2

I tested the following method using sendAsynchronousRequest:queue:completionHandler: as the method to download data from the URL. It seems to work fine, I can get the else clause to fire, either by messing up the URL or making the timeout interval .1 seconds.

    NSURL *theURL = [NSURL URLWithString:@"http://www.wccca.com/PITS/"];

    NSURLRequest *theRequest = [NSURLRequest requestWithURL:theURL cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:5];
    [NSURLConnection sendAsynchronousRequest:theRequest queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
        if (error == nil) {
            //do whatever with the data.  I converted it to a string for testing purposes.
            NSString *text = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
            NSLog(@"%@",text);
        }else{
            NSLog(@"%@",error.localizedDescription);
            UIAlertView *message = [[UIAlertView alloc] initWithTitle:@"No Internet Connection" message:@"Please check your internet connection and pull down to refresh." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
            [message show];
        }
    }];