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POSubclassing UITableviewController to make template for Core Data
 

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    <p>I'm refactoring an application that's already in the app store. </p> <p>In this app, I have a UITabBar with two tabs. Each tab contains a tableview with a list of Customers and Inventory respectively. The tableview is backed by core data and I have methods in place to swipe the table view to change the sorting of the data.</p> <p>These two controllers are just the same bar the names of the entities I pass into the NSFetchedResultsController. My aim was to create a super class that would be a template of these two views (as we re-use these views in other apps) so we can rapidly prototype future projects.</p> <p>However, my attempts have failed. I know the problem lies in the NSFetchedResultsController, but I just don't know why. When I try to run the app it fires the error </p> <pre><code>Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil' </code></pre> <p>Here's my code for the super class and one of the view controllers. If anybody has any insights I'd be really grateful. </p> <p>FocusTableViewController.h</p> <pre><code>#import &lt;UIKit/UIKit.h&gt; @interface FocusTableViewController : UITableViewController&lt;NSFetchedResultsControllerDelegate, UISearchBarDelegate, UISearchDisplayDelegate, UITableViewDelegate, UITableViewDataSource&gt; { @protected //Remembering where the tableview was when you click through on an item CGPoint savedScrollPosition; //Our Shit for sorting NSString *dEntity; NSString *dCacheName; NSString *dSectionKey0; NSString *dSectionKey1; NSString *dSortKey0; NSString *dSortKey1; //The Current sorting criteria //These have to be mutable, so they can change NSMutableString *currentKey; NSMutableString *currentSectionKey; //Filter Predicate For Searching NSString *dFilterPredicate; } @property (nonatomic) BOOL searchIsActive; /** DAO **/ @property (nonatomic, strong) NSFetchedResultsController *fetchedResultsController; @property (nonatomic, strong) NSManagedObjectContext *managedObjectContext; @property (nonatomic, strong) UISearchDisplayController *searchDisplayController; /** Custom Constructor **/ - (id)initWithTitle:(NSString *)title; /** Search Bar **/ - (void)setupSearchBar; - (void)makeSearchBarActive:(id)sender; /** Sorting Methods **/ - (void)sortTableView; - (void)changeFetchData; @end </code></pre> <p>FocusTableViewController.m</p> <pre><code>#import "FocusTableViewController.h" #import "AppDelegate.h" @interface FocusTableViewController () - (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath; @end @implementation FocusTableViewController @synthesize fetchedResultsController = __fetchedResultsController; @synthesize managedObjectContext = __managedObjectContext; @synthesize searchDisplayController = __searchDisplayController; @synthesize searchIsActive; - (id)initWithTitle:(NSString *)title { self = [super initWithStyle:UITableViewStylePlain]; if (self) { self.title = title; [self setupSearchBar]; self.tableView.dataSource = self; self.tableView.delegate = self; } return self; } - (id)initWithStyle:(UITableViewStyle)style { self = [super initWithStyle:style]; if (self) { } return self; } - (void)viewDidLoad { [super viewDidLoad]; if (__managedObjectContext == nil) { __managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; } self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemSearch target:self action:@selector(makeSearchBarActive:)]; } - (void)viewWillAppear:(BOOL)animated { [super viewWillAppear:animated]; if (savedScrollPosition.y == CGPointZero.y) { [self.tableView setContentOffset:CGPointMake(0, 44.f) animated:NO]; } else { [self.tableView setContentOffset:savedScrollPosition animated:NO]; } } - (void)viewDidUnload { [super viewDidUnload]; // Release any retained subviews of the main view. // e.g. self.myOutlet = nil; } - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation { return YES; } #pragma mark - Table view data source - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return [[self.fetchedResultsController sections] count]; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { id &lt;NSFetchedResultsSectionInfo&gt; sectionInfo = [[self.fetchedResultsController 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]; } [self configureCell:cell atIndexPath:indexPath]; return cell; } - (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath { NSManagedObject *managedObject = [self.fetchedResultsController objectAtIndexPath:indexPath]; if ([currentKey isEqualToString:dSortKey0]) { cell.textLabel.text = [[managedObject valueForKey:@"title"] description]; } else { cell.textLabel.text = [NSString stringWithFormat:@"%@ - %@",[[managedObject valueForKey:@"accountno"] description],[[managedObject valueForKey:@"title"] description]]; } } // Support rearranging the table view. - (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath { } // Support conditional rearranging of the table view. - (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath { return YES; } #pragma mark - Table View Customisation // Creates the scrubber on the right hand side of the list - (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView { if (searchIsActive) { return [__fetchedResultsController sectionIndexTitles]; } else { return [[NSArray arrayWithObject:@"{search}"]arrayByAddingObjectsFromArray:[__fetchedResultsController sectionIndexTitles]]; } } - (NSInteger) tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index { if (index == 0) { [tableView setContentOffset:CGPointZero animated:NO]; return NSNotFound; } return index; } - (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { if (!(section == 0 &amp;&amp; [self.tableView numberOfSections] == 1)) { id &lt;NSFetchedResultsSectionInfo&gt; sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section]; return [sectionInfo name]; } return nil; } #pragma mark - Table view delegate #pragma mark - Search Bar - (void)setupSearchBar { UISearchBar *mySearchBar = [[UISearchBar alloc] init]; mySearchBar.delegate = self; [mySearchBar setAutocapitalizationType:UITextAutocapitalizationTypeNone]; [mySearchBar sizeToFit]; self.tableView.tableHeaderView = mySearchBar; __searchDisplayController = [[UISearchDisplayController alloc] initWithSearchBar:mySearchBar contentsController:self]; [self setSearchDisplayController:__searchDisplayController]; [__searchDisplayController setDelegate:self]; [__searchDisplayController setSearchResultsDataSource:self]; } - (void)makeSearchBarActive:(id)sender { [__searchDisplayController setActive:YES animated:YES]; } #pragma mark - #pragma mark Content Filtering - (void)filterContentForSearchText:(NSString*)searchText scope:(NSString*)scope { [NSFetchedResultsController deleteCacheWithName:dCacheName]; NSFetchRequest *aRequest = [[self fetchedResultsController] fetchRequest]; NSPredicate *predicate = [NSPredicate predicateWithFormat:dFilterPredicate, searchText]; [aRequest setPredicate:predicate]; NSError *error = nil; if (![[self fetchedResultsController] performFetch:&amp;error]) { //_ERROR_ Save Error } } #pragma mark - #pragma mark UISearchDisplayController Delegate Methods - (void)searchDisplayControllerWillBeginSearch:(UISearchDisplayController *)controller { [self setSearchIsActive:YES]; } - (void)searchDisplayControllerDidEndSearch:(UISearchDisplayController *)controller { [NSFetchedResultsController deleteCacheWithName:dCacheName]; self.fetchedResultsController = nil; //For some reason the iPad version can't calculate whether there's a navbar or not //see : http://stackoverflow.com/questions/6591674/uisearchdisplaycontroller-gray-overlay-not-fully-covering-table if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone) { [self.tableView setContentOffset:CGPointMake(0, 44.f) animated:NO]; } } - (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchString:(NSString *)searchString { [self filterContentForSearchText:searchString scope:[[self.searchDisplayController.searchBar scopeButtonTitles] objectAtIndex:[self.searchDisplayController.searchBar selectedScopeButtonIndex]]]; // Return YES to cause the search result table view to be reloaded. return YES; } - (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchScope:(NSInteger)searchOption { [self filterContentForSearchText:[self.searchDisplayController.searchBar text] scope:[[self.searchDisplayController.searchBar scopeButtonTitles] objectAtIndex:searchOption]]; // Return YES to cause the search result table view to be reloaded. return YES; } - (void)searchDisplayControllerDidBeginSearch:(UISearchDisplayController *)controller { /* Because the searchResultsTableView will be released and allocated automatically, so each time we start to begin search, we set its delegate here. */ [self.searchDisplayController.searchResultsTableView setDelegate:self]; } #pragma mark - Sort Table View - (void)changeFetchData { self.fetchedResultsController.delegate = nil; __fetchedResultsController = nil; NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:dEntity inManagedObjectContext:__managedObjectContext]; [fetchRequest setEntity:entity]; NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:currentKey ascending:YES selector:@selector(caseInsensitiveCompare:)]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; [fetchRequest setSortDescriptors:sortDescriptors]; NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:__managedObjectContext sectionNameKeyPath:currentSectionKey cacheName:nil]; self.fetchedResultsController = aFetchedResultsController; __fetchedResultsController.delegate = self; NSError *error; if (![[self fetchedResultsController] performFetch:&amp;error]) { //_ERROR_ // Update to handle the error appropriately. NSLog(@"Fetch failed"); NSLog(@"Unresolved error %@, %@", error, [error userInfo]); exit(-1); // Fail } [self.tableView reloadData]; } - (void)sortTableView { if ([currentKey isEqualToString:dSortKey0]) { [currentKey setString:dSortKey1]; [currentSectionKey setString:dSectionKey1]; } else if ([currentKey isEqualToString:dSortKey1]) { [currentKey setString:dSortKey0]; [currentSectionKey setString:dSectionKey0]; } [NSFetchedResultsController deleteCacheWithName:dCacheName]; [self.tableView reloadData]; [self changeFetchData]; } #pragma mark - Fetched results controller - (NSFetchedResultsController *)fetchedResultsController { if (__fetchedResultsController != nil) { return __fetchedResultsController; } // Create the fetch request for the entity. NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; // Configure the Entity NSEntityDescription *entity = [NSEntityDescription entityForName:dEntity inManagedObjectContext:__managedObjectContext]; [fetchRequest setEntity:entity]; [fetchRequest setFetchBatchSize:20]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"deleted == 0"]; [fetchRequest setPredicate:predicate]; //Configure Sort Descriptors NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:currentKey ascending:YES selector:@selector(caseInsensitiveCompare:)]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; [fetchRequest setSortDescriptors:sortDescriptors]; [fetchRequest setReturnsObjectsAsFaults:NO]; // nil for section name key path means "no sections". NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:__managedObjectContext sectionNameKeyPath:currentSectionKey cacheName:dCacheName]; aFetchedResultsController.delegate = self; self.fetchedResultsController = aFetchedResultsController; NSError *error = nil; if (![self.fetchedResultsController performFetch:&amp;error]) { //_ERROR_ NSLog(@"The error is %@",error); } return __fetchedResultsController; } #pragma mark - Fetched results controller delegate - (void)controllerWillChangeContent:(NSFetchedResultsController *)controller { if ([self searchIsActive]) { [[[self searchDisplayController] searchResultsTableView] beginUpdates]; } else { [self.tableView beginUpdates]; } } - (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id &lt;NSFetchedResultsSectionInfo&gt;)sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type { switch(type) { case NSFetchedResultsChangeInsert: [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeDelete:[self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade]; break; } } - (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath { UITableView *tableView = self.tableView; switch(type) { case NSFetchedResultsChangeInsert: [tableView insertRowsAtIndexPaths: [NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeDelete: [tableView deleteRowsAtIndexPaths: [NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeUpdate: [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath]; break; case NSFetchedResultsChangeMove: [tableView deleteRowsAtIndexPaths: [NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; [tableView insertRowsAtIndexPaths: [NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade]; break; } } - (void)controllerDidChangeContent:(NSFetchedResultsController *)controller { if ([self searchIsActive]) { [[[self searchDisplayController] searchResultsTableView] endUpdates]; } else { [self.tableView reloadData]; [self.tableView endUpdates]; } } @end </code></pre> <p>The CustomerViewController_iPhone.h is blank and here's the .m</p> <pre><code>#import "CustomerViewController_iPhone.h" #import "CustomerDetailViewController_iPhone.h" @interface CustomerViewController_iPhone () @end @implementation CustomerViewController_iPhone - (id)initWithTitle:(NSString *)title { self = [super initWithTitle:title]; if (self) { dEntity = @"Customer"; dCacheName = @"Customer_Cache"; dSectionKey0 = @"nameFirstLetter"; dSectionKey1 = @"accountNoFirstNumber"; dSortKey0 = @"title"; dSortKey1 = @"accountno"; dFilterPredicate = @"(title contains[cd] %@ OR accountno contains[cd] %@) AND deleted == 0"; } return self; } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. currentKey = [dSortKey0 mutableCopy]; currentSectionKey = [dSectionKey0 mutableCopy]; } - (void)viewDidUnload { [super viewDidUnload]; // Release any retained subviews of the main view. } -(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { savedScrollPosition = [tableView contentOffset]; CustomerDetailViewController_iPhone *detail = [[CustomerDetailViewController_iPhone alloc] initWithNibName:@"CustomerDetailViewController_iPhone" bundle:nil]; [self.navigationController pushViewController:detail animated:YES]; } @end </code></pre> <h1>EDIT</h1> <p>I can't answer my own question yet for another 3 hours because I don't have enough reputation. Here's what I wrote:</p> <p>I've found the problem. When I instantiate the view controller, the first time the NSFetchedResultsController is being called, the variables requires are null. Stupid I know. Maybe, if I had of posted this snippet of code earlier, someone may have picked up on the answer.</p> <pre><code>/** Set up the Customers TableView **/ NSString *customerTitle = NSLocalizedString(@"Customers", @"The user's list of customers"); CustomerViewController_iPhone *customers = [[CustomerViewController_iPhone alloc] initWithTitle:customerTitle]; UINavigationController *customers_nav = [[UINavigationController alloc] initWithRootViewController:customers]; </code></pre> <p>Thanks to Nikita and Phillip for the help. </p>
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    1. COSo,where specificly does this error occure?It's hard to read all of your code to find it out)
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      1. USNikita Pestrov
    2. COThat's the thing, I don't know. It crashes on launch. Sometimes when simulator/device crashes it just highlights the **return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));** in main and other times it highlights **NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:__managedObjectContext sectionNameKeyPath:currentSectionKey cacheName:dCacheName];** in FocusTableViewController.m
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    3. COIf you use the Breakpoint navigator window to set a break on uncaught Objective-C exceptions, it **should** stop where it encounters the error and show you the stack. If that fails, try wrapping that line in main.m in a @try/@catch block and logging the exception plus its call stack symbols.
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      1. POSubclassing UITableviewController to make template for Core Data
      1. USPhillip Mills
 

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