Using IBOutletCollections

Question

I have 30 UILabels I wish to use as IBOutlets. However when I try to access their UILabel properties I'm getting errors telling me that property x is not found for object of type 'id'. I'm very rusty with Objective C so suspect I've done something fundamentally wrong. I've assigned all my labels to the IBCollection within the xib file.

.h

@interface ViewController : UIViewController
{
    IBOutletCollection(UILabel) NSArray *statPanels;
}
@property(retain) IBOutletCollection(UILabel) NSArray *statPanels;
@end

.m

@interface ViewController ()
@end

@implementation ViewController
@synthesize statPanels;

- (void)viewDidLoad
{
    [super viewDidLoad];

    statPanels = [[NSArray alloc] initWithObjects:[UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], nil ];

    [statPanels objectAtIndex:3].hidden = YES;
}

Answer 1

If you connected all of the labels in interface builder then you don't have to initialize the statPanels array.

Delete this line:

statPanels = [[NSArray alloc] initWithObjects:[UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], nil ];

That line is creating a new array and a bunch of new labels, and losing your outlets.

Also, you will need to cast like the other answer is saying:

((UILabel *) [statPanels objectAtIndex:3]).property = ....

Answer 2

I think you should use cast; NSArray only knows it contains a bunch of id's. So you need to do something like

((UILabel *)[array objectAtIndex:0]).someProperty

Also you should have alloc init rather than only alloc. Also in your ivar declaration you don't need IBOutlet... and stuff. Just NSArray. (In relatively new versions of XCode you don't need to declare ivar at all.)

Answer 3

When nibs are deserialized, the objects specified in them are instantiated and assigned to their outlets. You don't have to instantiate the objects yourself, and by doing so, you're losing the only reference you have to the labels in question.

Basically, you just need to delete this line:

    statPanels = [[NSArray alloc] initWithObjects:[UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], [UILabel alloc], nil ];

You should also be aware that allocating objects without calling any initialiser is bound to end badly. You aren't supposed to do this. The usual pattern in Objective-C is to call [[Foo alloc] init] or similar.