UITableView dataSource must return a cell from tableView: cellForRowAtIndexPath

Question

I have set up a UIViewController with a table view and cell added. The delegate and data source are linked to the table view. However I getting this error and I am confused as to why. The code works when I use it with a UITableViewController but not with a UIViewcontroller. The reason for wanting to use a UIViewController is that the navigation bar scrolls with the table when using a UITableViewController and I was advised on here to use a UIViewController and add the Table view.

#import "ObViewControllerObservationsTable.h"
#import "ObAppDelegate.h"
#import "Observations.h"
#import "ObViewControllerTableDetail.h"
#import "ObViewControllerMainMenu.h"

@interface ObViewControllerObservationsTable ()

@property (nonatomic, strong) NSArray *teacherNames;
@property (nonatomic, readonly) NSManagedObjectContext *managedObjectContext;
@property (weak, nonatomic) IBOutlet UIBarButtonItem *detailsButton;
@end

@implementation ObViewControllerObservationsTable

- (void)viewDidLoad
{
[super viewDidLoad];
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Observations"];
fetchRequest.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"obsTeacherName" ascending:YES]];
NSError *error = nil;
self.teacherNames = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
[self.tableView reloadData];
}

- (NSManagedObjectContext *) managedObjectContext
{
return [(ObAppDelegate *) [[UIApplication sharedApplication] delegate] managedObjectContext];
}

- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return self.teacherNames.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"teacherCell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
Observations *currentList = [self.teacherNames objectAtIndex:indexPath.row];
cell.textLabel.text = currentList.obsID;
return cell;
}

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
if (editingStyle == UITableViewCellEditingStyleDelete) {
[self.managedObjectContext deleteObject:[self.teacherNames objectAtIndex:indexPath.row]];
    [self.managedObjectContext save:nil];

    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Observations"];
    fetchRequest.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"obsTeacherName" ascending:YES]];
    NSError *error = nil;
    self.teacherNames = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
    if (self.teacherNames.count == 0)
    {
        self.detailsButton.enabled = NO;
    }
    else
    {
        self.detailsButton.enabled = YES;
    }
    [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
}
else if (editingStyle == UITableViewCellEditingStyleInsert) {
}
}

#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
obsID = [[self.teacherNames objectAtIndex:indexPath.row] obsID];
self.detailsButton.enabled = YES;
}

Answer 1

dequeueReusableCellWithIdentifier: returns nil if no reusable object exists in the reusable-cell queue. (See UITableView reference).

Here is how it should be:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"teacherCell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
        // More initializations if needed.
    }
    Observations *currentList = [self.teacherNames objectAtIndex:indexPath.row];
    cell.textLabel.text = currentList.obsID;
    return cell;
}

Answer 2

I think the problem is the dequeueReusableCellWithIdentifier method. I tried a quick sample project with a tableView in a view controller rather than in a UITableViewController and encountered the error you describe. When I manually generated the cell using

[UITableViewCell *cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"testCell"];

it worked fine.