Question

I am currently developing an iPhone application which loads data from an RSS feed and displays it in a Tab Bar Application in 2 UITableViews, which we we call TableViewA and TableViewB. In the AppDelegate we have the following method:

- (void)getDataWithContext:(NSManagedObjectContext *)context
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    NSError *parseError = nil;

    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;

    XMLReader *xmlReader = [[[XMLReader alloc] initWithContext:context]autorelease];
    [xmlReader parseXMLFileAtURL:[NSURL URLWithString:@"http://example.com/rss.xml"] parseError:&parseError];
    [pool release];

    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}

In our applicationDidFinishLaunching: method we call detach a new thread with that selector:

if ([self isDataSourceAvailable] == NO) {
    UIAlertView *noConnection = [[[UIAlertView alloc] initWithTitle:@"Connection Unavailable" message:@"The connection to the database is unavailable. The information displayed may be outdated." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil] autorelease];
    [noConnection show];
}
else{
    [NSThread detachNewThreadSelector:@selector(getDatawithContext:) toTarget:self withObject:context];
}

TableViewControllerA is a UITableViewController

with the following methods that load the data and images for the TableView. When the thread of the XML reader from above exits, having placed all entries into CoreData, we receive the notification and reload the entries into the TableView from CoreData.

TableViewControllerB is a TableViewControllerA which inherits these same methods with a few changes to select different entries from the database.

- (IBAction)loadData: (id) sender{
    BroadwayAppDelegate *appDelegate = (BroadwayAppDelegate *) [[UIApplication sharedApplication] delegate];

    checkDate = [NSPredicate predicateWithFormat: @"date <= %@",
                        [NSDate date]];
    if ( [self.showsSegmentedControl selectedSegmentIndex] == UISegmentedControlNoSegment || 
            [self.showsSegmentedControl selectedSegmentIndex] == 0){
        self.listContent = [CoreDataHelper searchObjectsInContext :@"Entry" :self.checkDate :@"title" :YES :appDelegate.managedObjectContext];
    }
    else if ([self.showsSegmentedControl selectedSegmentIndex] == 1){
        self.listContent = [CoreDataHelper searchObjectsInContext :@"Entry" :self.checkDate :@"startDate" :NO :appDelegate.managedObjectContext];
    }
    else if ([self.showsSegmentedControl selectedSegmentIndex] == 2){
        self.listContent = [CoreDataHelper searchObjectsInContext :@"Entry" :self.checkDate :@"endDate" :YES :appDelegate.managedObjectContext];
    }
    else if ([self.showsSegmentedControl selectedSegmentIndex] == 3){
        self.listContent = [CoreDataHelper searchObjectsInContext :@"Entry" :self.checkDate :@"type" :YES :appDelegate.managedObjectContext];
    }

    // create a filtered list that will contain products for the search results table.
    self.filteredContent = [NSMutableArray arrayWithCapacity:[self.listContent count]];

    // restore search settings if they were saved in didReceiveMemoryWarning.
    if (self.savedSearchTerm)
    {
        [self.searchDisplayController setActive:self.searchWasActive];
        [self.searchDisplayController.searchBar setSelectedScopeButtonIndex:self.savedScopeButtonIndex];
        [self.searchDisplayController.searchBar setText:savedSearchTerm];

        self.savedSearchTerm = nil;
    }

    NSError *error;
    [appDelegate.managedObjectContext save:&error];


    [self.tableView reloadData];

}

 - (void)viewDidLoad {
     [super viewDidLoad];
     [self loadData:nil];
     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(threadExited) name:@"NSThreadWillExitNotification" object:nil];

     dateFormatter = [[NSDateFormatter alloc]init];
     [dateFormatter setDateStyle: NSDateFormatterMediumStyle];
     self.title = @"Entries";

 }

- (void)threadExited{
    [self loadData:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    [NSThread detachNewThreadSelector:@selector(loadImages) toTarget:self withObject:nil];
}
- (void) loadImages{

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    NSArray *coreDataEntries = [CoreDataHelper getObjectsFromContext:@"Entry" :@"title" :NO :appDelegate.managedObjectContext];
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
    for (Entry *s in coreDataEntries){
        if (s.image == nil) {
            NSString *URLString = [[Entry imageURLFromLink:s.link withExtension:@".jpg"]absoluteString];
            NSURL *imageURL = [NSURL URLWithString:URLString];
            NSData *imageData = [NSData dataWithContentsOfURL:imageURL];
            s.image = [UIImage imageWithData:imageData];
        }
    }
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
    [self.tableView reloadData];
    [pool release];
}

The application crashes if the user is scrolling either tableview when the data is reloaded or possibly when the XML reader exits. Why is this happening and how can we fix it? We have used the provided tools to check for memory leaks and things of that sort, and we did not find any relevant to the crash.

Answer 1

Run with debug mode! When application is crashes click on “Show Debugger” button

_{(source: gyazo.com)}

and look at the problem

or look on video