Table View in View Controller using Core Data - core-data

Question

I am using core data and am trying to add table view cells to a table view in a view controller. When I implement it in a table view controller the app runs. When I run it when the table view is part of another view controller, the app does not run. It shows an error in the code: property tableview not found on object of type DeviceViewController. DeviceViewController.h has a table view data source and delegate. My code is:
#import "DeviceViewController.h"
#import "DeviceDetailViewController.h"
#interface DeviceViewController ()
#property (strong) NSMutableArray *devices;
#end
#implementation DeviceViewController
- (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];
// self.navigationItem.rightBarButtonItem = self.editButtonItem;
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
// Fetch the devices from persistent data store
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:#"Device"];
self.devices = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
[self.tableView reloadData];
}
- (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.devices.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
// Configure the cell...
NSManagedObject *device = [self.devices objectAtIndex:indexPath.row];
[cell.textLabel setText:[NSString stringWithFormat:#"%# ", [device valueForKey:#"name"]]];
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.devices objectAtIndex:indexPath.row]];
NSError *error = nil;
if (![context save:&error]) {
NSLog(#"Can't Delete! %# %#", error, [error localizedDescription]);
return;
}
// Remove device from table view
[self.devices removeObjectAtIndex:indexPath.row];
[self. otableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
}
}

Answer 1

As I see it, in this case, it has nothing to do with CoreData.
You should add the UITableViewDataSource and UITableViewDelegate protocols to your VC.
After that you should create a UITableView (you can do it in interface builder) and connect the datasource and delegate to your view controller.
You can also add a property for the UITableView in your VC.
When you use UITableViewController, all this is done from Xcode, but if you use UITableView inside a regular UIViewController you should take care of this stuff.
Good Luck!
EDIT:
Add this as a propert
#property (nonatomic, strong) UITableView *deviceTableView;
Change the viewDidLoad method to this:
- (void)viewDidLoad {
[super viewDidLoad];
_deviceTableView = [[UITableView alloc] initWithFrame:self.view.frame];
_deviceTableView.delegate = self;
_deviceTableView.dataSource = self;
[self.view addSubview:_deviceTableView];
[_deviceTableView reloadData];
}
Delete what you have written in viewDidAppear and replace self.tableView with _deviceTableView everywhere in this file.

Answer 2

Another problem that could be causing the crashes is if your NSManagedObjectContext is nil when you are trying to execute the fetch request. I would add an if([self managedObjectContext])
before using it in any of your view hierarchy methods.
Also, you should be careful when using views instantiated from storyboards. Nikola's answer said to add the code configuring the view controller in viewDidLoad, and that is ok as long as you did not drag a UITableView onto your UIViewController instance in interface builder. If you already have created and linked a tableview in interface builder, you will be needlessly replacing it with a new one, so before the
_deviceTableView = [[UITableView alloc] initWithFrame:self.view.frame];
line, you should add an if(!_deviceTableView)
statement because it will prevent you from adding a second table view to your view. The issue is that if you have already added a tableview in IB, it will be retained by your view even after you change your tableview property, so it is possible to have two tables show up.
Alternatively, you could use "lazy instantiation" in your getter method for the table view property to make sure it is initialized when you access it.
Lastly, in order to help give us a better idea of why your app is crashing it would be helpful to get the exception log from the console in Xcode.