[iPhone SDK] Why can't I message UI elements or other classes?

Question

Hi there,
I confess to being a bit of a new hand at Cocoa -- I've been working through Aaron Hillegass's excellent book on the subject. Still, I haven't had any trouble like what I'm about to describe.
Everything was going swimmingly until I switched from noodling in desktop development over to Cocoa Touch. Here is an example application project using Apple's view-based app template to illustrate:
http://danilocampos.com/development/WTFXcode.zip (1.3 MB)
An IBOutlet, UILabel *label, is declared in the app delegate header. In the app delegate's implementation, several lines are dedicated to logging statements showing that applicationDidFinishLaunching was called and detailing my attempt to send messages to label. Sending setText to label fails, as does sending text to query its data. An NSAssert is called to compare the label's contents to the value it was sent. Assertion fails and app closes. Obviously, even if I comment out my assertion the app still isn't doing what it should. Everything compiles fine and the compiler doesn't log any warnings.
The ViewController nib has a UICustomObject for the app delegate. From there, the app delegate is wired to the UILabel.
Where am I going wrong here? Did Garbage Collection on the desktop environment spoil me and I'm forgetting to allocate something?
Also: It's not included in the example I uploaded, but I'm having the same trouble with sending messages to other NSObject sub-classes I make, even if I properly instantiate them and set them up as properties like in Apple's app templates. If anyone has a thought about that issue, I'd love to hear it too.
Thanks!
Message was edited by: Danilo Campos

Answer 1

I could be wrong on this, but I don't think you should have a reference to the AppDelegate in your NIB file. Get rid of that, and the IBOutlet definition in your AppDelegate.h.
In your viewController is where you should define the IBOutlet, and then wire it to the File's Owner instead of the AppDelegate.
You can still have a label stored in the app delegate, but you'd have to instantiate it using code, and then call an accessor in your view controller to get the pointer.
AppDelegate
-- .h --
@interface WTFXcodeAppDelegate : NSObject <UIApplicationDelegate> {
UIWindow *window;
WTFXcodeViewController *viewController;
UILabel *label;
-- .m --
- (void)applicationDidFinishLaunching:(UIApplication *)application {
// Override point for customization after app launch
[window addSubview:viewController.view];
[window makeKeyAndVisible];
label = [[UILabel alloc] init];
NSLog(@"applicationDidFinishLaunching: %@", application);
NSString *theString = @"Update, **** you!";
NSLog(@"The string: %@",theString);
[label setText:theString];
NSString *labelText = [label text];
NSLog(@"Trying to message the label and ask for its text value: %@", labelText);
NSAssert(labelText == theString, @"The label text should match theString");
- (void)dealloc {
[label release];
// Rest of the releases
WTFViewController
-- .h --
@interface WTFXcodeViewController : UIViewController {
IBOutlet UILabel *label;
@property (nonatomic, retain) UILabel *label;
-- .m --
@synthesize label;
- (void)viewDidLoad {
label = //Some method in the app delegate to return your label
[super viewDidLoad];
- (void)dealloc {
[label release];
[super dealloc];