problem with "this class is not key value coding-compliant"

Question

Hi,

I know the meaning of this error, but I'm really struggling with it, and I need someone's help :

2010-09-21 15:03:11.562 Stocks[5605:207] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<NSObject 0x499fb20> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key actionText.'

There is my code here :

AlertCell.h

#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>


@interface AlertCell : UITableViewCell {
    IBOutlet UILabel *actionText;
}

@property (retain, nonatomic) UILabel *actionText;

@end

And AlertCell.m

@implementation AlertCell
@synthesize actionText;


- (void)dealloc {
    [actionText release];
    [super dealloc];
}


@end

The problem happens just there :

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    static NSString *CellIdentifier = @"Cell";

    AlertCell *cell = (AlertCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {
        NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"AlertCell" owner:nil options:nil];
        for (id oneObject in nib) {
            if ([oneObject isKindOfClass:[UITableViewCell class]]) {
                cell = (AlertCell *)oneObject;
                break;
            }
        }
    }    


    cell.actionText.text = [arrayAlert objectAtIndex:indexPath.row];
    return cell;
}

On this line :

NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"AlertCell" owner:nil options:nil];

As asked, here is my header for the TableViewCOntroller :

#import <UIKit/UIKit.h>


@interface AlertesViewController : UITableViewController {
    NSMutableArray *arrayAlert;
}

And you can see my XIB file (as XML): http://pastebin.com/FDVzLYZu

@end

Can anyone help me ? Thanks a lot !s

Answer 1

There are a couple of options to resolve this - i'll let you decide which is the most appropriate.

The reason it's failing is because the owner is being passed as nil. You're binding the actionText outlet to the file's owner in IB, but then when loading the nib, the owner is nil. I'd guess that when loading with a nil owner behind the scenes an NSObject is used, which is why you're getting the key/value error.

My previous advice to pass the cell as the owner would also fail as I didn't know how the Nib is constructed; the cell is nil as you've yet to create it (and dequeue is passing nil back, so even pass cell as the owner is still essentially passing nil).

Two options:

• Instantiate a new cell in your -cellForRowAtIndexPath:(NSIndexPath *)indexPath implementation, and pass that new cell as the owner (but i'd guess that this isn't the best solution for you)
• Or, and I'd suggest this is the better solution, change the binding of actionText in your nib file to the Alert Cell and not the file's owner (You have File's Owner and an Alert Cell - bind the UILabel to the actionText outlet of the Alert Cell, and not the File's owner, which is what's being done at present) - I suspect this is what you want. With that in mind file's owner can become an NSObject again.

------- Original answer kept below as the file's owner class is also a common cause for this error -------

It suggests that you've 'instantiated' an AlertCell in InterfaceBuilder, and you're binding something to actiontext, but the class isn't set to AlertCell, it's still NSObject?

Take a look at the class text box on the identify tab of the tool palette for that object in Interface Builder. The class should be AlertCell, but i'd guess it's still set to NSObject.

As an aside, and feel free to ignore this advice, but there are a couple of extra things i'd encourage you to do, purely from an Objective C expectations/conventions point of view:

• Name your files after your class (upper case the first character of the filename).
• Prefix your class names; two uppercase characters, typically your initials (i'd name it DWAlertCell, for example).