NSFetchedResultsController Help - objective-c

Question

My table view is showing nothing (even though there is data), and when I switch back to it from a tab bar I get an error:
2011-06-28 11:25:20.043 Paparazzi[7773:207] -[__NSCFArray sections]: unrecognized selector sent to instance 0x592d2d0
2011-06-28 11:25:20.048 Paparazzi[7773:207] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFArray sections]: unrecognized selector sent to instance 0x592d2d0'
What am I doing wrong?
You can get the full code at:
https://github.com/blasto333/Paparazzi
Header
#interface PersonListViewController : UITableViewController {
NSFetchedResultsController *fetchResultsController;
}
#end
Implementation
- (void)viewDidLoad
{
[super viewDidLoad];
// Uncomment the following line to preserve selection between presentations.
// self.clearsSelectionOnViewWillAppear = NO;
// Uncomment the following line to display an Edit button in the navigation bar for this view controller.
// self.navigationItem.rightBarButtonItem = self.editButtonItem;
fetchResultsController = [[FlickrFetcher sharedInstance] fetchedResultsControllerForEntity:#"Person" withPredicate:nil];
}
- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
}
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
}
- (void)viewDidDisappear:(BOOL)animated
{
[super viewDidDisappear:animated];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
// Return YES for supported orientations
return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
#pragma mark - Table view data source
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return [[fetchResultsController sections] count];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
id <NSFetchedResultsSectionInfo> sectionInfo = [[fetchResultsController sections] objectAtIndex:section];
return [sectionInfo numberOfObjects];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
// Configure the cell...
Person *person = [fetchResultsController objectAtIndexPath:indexPath];
[cell.textLabel setText:person.name];
return cell;
}

Answer 1

You need to retain the fetchResultsController because it's being released as soon as it is created. The method fetchedResultsControllerForEntity:withPredicate returns an autoreleased object. Change the line to read:
fetchResultsController = [[[FlickrFetcher sharedInstance] fetchedResultsControllerForEntity:#"Person" withPredicate:nil] retain];
Intense memory management on iOS and Mac OS is going to be a thing of the past soon enough though. If you're a paying ADC member, go check out some of the beta releases of Xcode and test drive the automatic reference counting stuff. I've been using it for a few weeks and it's been great.
EDIT: You're not getting any rows to show up because your fetchResultsController doesn't have any data in it. The method numberOfSectionsInTableView: is returning zero, so none of your other methods for the TableViewDataSource protocol are even being called.