Question

I am loading in data to a UITableView, from a custom UITableViewCell (own class and nib). It works great, until I try to access the objectAtIndex:indexPath.row for some arrays.

I’ll post my code first, it will probably be easier for you to understand what I mean then.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *CellIdentifier = @"CustomCell";
    CustomCell *cell = (CustomCell *) [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil){
        NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:@"CustomCell" owner:self options:nil];
        for (id currentObject in topLevelObjects){
            if ([currentObject isKindOfClass:[CustomCell class]]){
                cell = (CustomCell *) currentObject;
                break;
            }
        }
    }
    // Configure the cell...
    NSUInteger row = indexPath.row;
    cell.titleLabel.text = [postsArrayTitle objectAtIndex:indexPath.row];
    cell.dateLabel.text = [postsArrayDate objectAtIndex:indexPath.row];
    cell.cellImage.image = [UIImage imageWithContentsOfFile:[postsArrayImgSrc objectAtIndex:indexPath.row]];

    return cell;
}

The odd thing is, it does work when it loads in the first three cells (they are 130px high), but crashes when I try to scroll down. (Aka, the log shows three numbers before it crashes, 0, 1, 2)

So, as a summary, the objectAtIndex:indexPath.row runs 3*3 times successfully, but when I try to scroll down in the app, loading in new cells, the app crashes with the following error:

2010-05-30 14:00:43.122 app[2582:207] -[NSCFString objectAtIndex:]: unrecognized selector sent to instance 0x5a44bf0
2010-05-30 14:00:43.124 app[2582:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString objectAtIndex:]: unrecognized selector sent to instance 0x5a44bf0'
// Stack
    0   CoreFoundation                   0x02398c99 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x024e65de objc_exception_throw + 47
    2   CoreFoundation                  0x0239a7ab -[NSObject(NSObject) doesNotRecognizeSelector:] + 187
    3   CoreFoundation                  0x0230a496 ___forwarding___ + 966
    4   CoreFoundation                  0x0230a052 _CF_forwarding_prep_0 + 50
    5   myappname                        0x00002ab1 -[HomeTableViewController tableView:cellForRowAtIndexPath:] + 605

---

Additional information on the arrays:

The arrays are created in the .h file:

NSArray *postsArrayDate;
NSArray *postsArrayTitle;
NSArray *postsArrayComments;
NSArray *postsArrayImgSrc;

And filled in the viewDidLoad::

NSURL *urlPosts = [NSURL URLWithString:@"http://mysite/myphpfile.php?posts=2"]; //returns data in this format: DATA1#Data1.1#data1.2~DATA2#data2.1#~ and so on.
NSError *lookupError = nil;
NSString *data = [[NSString alloc] initWithContentsOfURL:urlPosts encoding:NSUTF8StringEncoding error:&lookupError];
postsData = [data componentsSeparatedByString:@"~"];
[data release], data = nil;
urlPosts = nil;
postsArrayDate = [[postsData objectAtIndex:2] componentsSeparatedByString:@"#"];
postsArrayTitle = [[postsData objectAtIndex:3] componentsSeparatedByString:@"#"];
postsArrayComments = [[postsData objectAtIndex:4] componentsSeparatedByString:@"#"];
postsArrayImgSrc = [[postsData objectAtIndex:5] componentsSeparatedByString:@"#"];

How can I fix this crash?

Answer 1

The actual error is this:

-[NSCFString objectAtIndex:]: unrecognized selector sent to instance 0x5d10c20

In other words, you tried to run objectAtIndex: on an NSString (NSCFString), which of course does not support this method.

You call objectAtIndex: three times, in these lines:

cell.titleLabel.text = [postsArrayTitle objectAtIndex:indexPath.row];
cell.dateLabel.text = [postsArrayDate objectAtIndex:indexPath.row];
cell.cellImage.image = [UIImage imageWithContentsOfFile:[postsArrayImg objectAtIndex:indexPath.row]];

So it appears that postsArrayTitle, postsArrayDate, or postsArrayImg isn’t an NSArray, but an NSString.