Core Data Crashing When Pushing to View - ios

Question

So this is my first time working with core data, and so far it hasn't been the best experience. My application so far consists of two UITableView controllers and a single ViewController. The app simply asks the user to enter the name of a list on UIAlert and it saves to core data, and the name of the list is put into the first tableview. So far so good. Then the user clicks on the name of the list and it pushes them to the contents on the list, which is empty because it hasn't been populated yet. So my problem is when I go to populate it my app just crashes. I don't even get to the the ViewController. I'm really lost I'll put the necessary code here if there's any more let me know. Thanks!
Error argv char ** 0xbfffeda8 0xbfffeda8
Data Model:
The .m To Add Items to the list:
- (NSManagedObjectContext *)managedObjectContext {
NSManagedObjectContext *context = nil;
id delegate = [[UIApplication sharedApplication] delegate];
if ([delegate performSelector:#selector(managedObjectContext)]) {
context = [delegate managedObjectContext];
}
return context;
}
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization
}
return self;
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (IBAction)cancel:(id)sender {
[self dismissViewControllerAnimated:YES completion:nil];
}
- (IBAction)save:(id)sender {
NSManagedObjectContext *context = [self managedObjectContext];
// Create a new managed object
NSManagedObject *newItem = [NSEntityDescription insertNewObjectForEntityForName:#"Item" inManagedObjectContext:context];
[newItem setValue:self.name.text forKey:#"itemName"];
[newItem setValue:self.price.text forKey:#"price"];
[newItem setValue:self.desc.text forKey:#"description"];
NSError *error = nil;
// Save the object to persistent store
if (![context save:&error]) {
NSLog(#"Can't Save! %# %#", error, [error localizedDescription]);
}
[self dismissViewControllerAnimated:YES completion:nil];
}
#end
The .m to show all the items in a list:
- (NSManagedObjectContext *)managedObjectContext {
NSManagedObjectContext *context = nil;
id delegate = [[UIApplication sharedApplication] delegate];
if ([delegate performSelector:#selector(managedObjectContext)]) {
context = [delegate managedObjectContext];
}
return context;
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
// Fetch the lists from persistent data store
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:#"Item"];
self.lists = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
self.items = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
[self.tableView reloadData];
}
- (id)initWithStyle:(UITableViewStyle)style
{
self = [super initWithStyle:style];
if (self) {
// Custom initialization
}
return self;
}
- (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;
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#pragma mark - Table view data source
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// Return the number of sections.
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
// Return the number of rows in the section.
return self.items.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
// Configure the cell...
NSManagedObject *item = [self.items objectAtIndex:indexPath.row];
[cell.textLabel setText:[item valueForKey:#"itemName"]];
return cell;
}
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
// Return NO if you do not want the specified item to be editable.
return YES;
}
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
NSManagedObjectContext *context = [self managedObjectContext];
if (editingStyle == UITableViewCellEditingStyleDelete) {
// Delete object from database
[context deleteObject:[self.items objectAtIndex:indexPath.row]];
NSError *error = nil;
if (![context save:&error]) {
NSLog(#"Can't Delete! %# %#", error, [error localizedDescription]);
return;
}
// Remove device from table view
[self.items removeObjectAtIndex:indexPath.row];
[self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
}
}
#pragma mark - Segue
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([[segue identifier] isEqualToString:#"ShowDetails"]) {
NSManagedObject *selectedItem = [self.items objectAtIndex:[[self.tableView indexPathForSelectedRow] row]];
AddViewController *destViewController = segue.destinationViewController;
destViewController.items = selectedItem;
}
}
#end
And the .m displaying all the lists:
- (NSManagedObjectContext *)managedObjectContext {
NSManagedObjectContext *context = nil;
id delegate = [[UIApplication sharedApplication] delegate];
if ([delegate performSelector:#selector(managedObjectContext)]) {
context = [delegate managedObjectContext];
}
return context;
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
// Fetch the lists from persistent data store
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:#"List"];
self.lists = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
self.items = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
[self.tableView reloadData];
}
- (id)initWithStyle:(UITableViewStyle)style
{
self = [super initWithStyle:style];
if (self) {
// Custom initialization
}
return self;
}
- (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;
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#pragma mark - Table view data source
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// Return the number of sections.
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
// Return the number of rows in the section.
return self.lists.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
// Configure the cell...
NSManagedObject *list = [self.lists objectAtIndex:indexPath.row];
[cell.textLabel setText:[list valueForKey:#"name"]];
return cell;
}
-(IBAction)add:(id)sender {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Add List" message:#"Create a New Wish List" delegate:self cancelButtonTitle:#"Cancel" otherButtonTitles:#"Save", nil];
[alert setAlertViewStyle:UIAlertViewStylePlainTextInput];
[alert setTag:2];
[alert show];
alert.delegate = self;
}
- (void) alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
if (buttonIndex != 0 && alertView.tag == 2) {
UITextField *tf = [alertView textFieldAtIndex:0];
NSManagedObjectContext *context = [self managedObjectContext];
// Create a new managed object
NSManagedObject *newList = [NSEntityDescription insertNewObjectForEntityForName:#"List" inManagedObjectContext:context];
[newList setValue:tf.text forKey:#"name"];
NSError *error = nil;
// Save the object to persistent store
if (![context save:&error]) {
NSLog(#"Can't Save! %# %#", error, [error localizedDescription]);
}
[self dismissViewControllerAnimated:YES completion:nil];
}
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:#"List"];
self.lists = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
self.items = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
[self.tableView reloadData];
}
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
// Return NO if you do not want the specified item to be editable.
return YES;
}
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
NSManagedObjectContext *context = [self managedObjectContext];
if (editingStyle == UITableViewCellEditingStyleDelete) {
// Delete object from database
[context deleteObject:[self.lists objectAtIndex:indexPath.row]];
NSError *error = nil;
if (![context save:&error]) {
NSLog(#"Can't Delete! %# %#", error, [error localizedDescription]);
return;
}
// Remove list from table view
[self.lists removeObjectAtIndex:indexPath.row];
[self.items removeObjectAtIndex:indexPath.row];
[self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
}
}
#end

Answer 1

You should consider using an NSFetchedResultsController to make your life easier, and your app more efficient.
This is incorrect:
self.lists = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
self.items = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
because these sets should contain different types of entity instance. But, you don't actually need self.items. The model contains a relationship between List and Item and you should just get the items for a specified list using that relationship (or a fetch request using the relationship) when you need it. And remove self.items, it's just confusing you. In the list view controller you don't need the items anyway.
When you push to show the items, you should be getting the selected List and passing that. So where you have destViewController.items = selectedItem; you should have something like destViewController.list = selectedList;, and then the item controller uses the relationship again to display the appropriate items.
And, when you add a new item, you have to associated it with self.list:
[newItem setValue:self.list forKey:#"list"];
You should also use managed object subclasses, and the best way to manage them is by using mogenerator.
Aside: Where you have if ([delegate performSelector: it should be if ([delegate respondsToSelector:, and probably log if you don't get a context back...