UINavigationController error crashing my app

I am trying my first UINavigationController app and it is now crashing. If I comment out the line that starts with navController, I don't crash, but if course the app doesn't work either.

(Note: My environment is IOS 4.2 and Xcode 3.2)

(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

    WpglViewController *firstViewController = [[WpglViewController alloc] init];    

    navController = [[UINavigationController alloc] initWithRootViewController:firstViewController];

    [firstViewController release];

    [window addSubview:navController.view];

    [self.window makeKeyAndVisible];

    return YES;
}

Here is the crash information. Can someone point me in the right direction? Thanks for the help.

2011-09-04 07:59:49.309 wpgl[7302:207] -[WpglViewController title]: unrecognized selector sent to instance 0x4b134c0
2011-09-04 07:59:49.313 wpgl[7302:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[WpglViewController title]: unrecognized selector sent to instance 0x4b134c0'
*** Call stack at first throw:

(
    0   CoreFoundation                      0x00ecdbe9 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x00cc25c2 objc_exception_throw + 47
    2   CoreFoundation                      0x00ecf6fb -[NSObject(NSObject) doesNotRecognizeSelector:] + 187
    3   CoreFoundation                      0x00e3f366 ___forwarding___ + 966
    4   CoreFoundation                      0x00e3ef22 _CF_forwarding_prep_0 + 50
    5   UIKit                               0x00375781 -[UINavigationController pushViewController:transition:forceImmediate:] + 743
    6   UIKit                               0x0036e4a0 -[UINavigationController pushViewController:animated:] + 62
    7   UIKit                               0x00370d98 -[UINavigationController initWithRootViewController:] + 78
    8   wpgl                                0x00001df9 -[wpglAppDelegate application:didFinishLaunchingWithOptions:] + 146
    9   UIKit                               0x002b81fa -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1163
    10  UIKit                               0x002ba55e -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 439
    11  UIKit                               0x002c4db2 -[UIApplication handleEvent:withNewEvent:] + 1533
    12  UIKit                               0x002bd202 -[UIApplication sendEvent:] + 71
    13  UIKit                               0x002c2732 _UIApplicationHandleEvent + 7576
    14  GraphicsServices                    0x016e4a36 PurpleEventCallback + 1550
    15  CoreFoundation                      0x00eaf064 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
    16  CoreFoundation         开发者_开发问答             0x00e0f6f7 __CFRunLoopDoSource1 + 215
    17  CoreFoundation                      0x00e0c983 __CFRunLoopRun + 979
    18  CoreFoundation                      0x00e0c240 CFRunLoopRunSpecific + 208
    19  CoreFoundation                      0x00e0c161 CFRunLoopRunInMode + 97
    20  UIKit                               0x002b9fa8 -[UIApplication _run] + 636
    21  UIKit                               0x002c642e UIApplicationMain + 1160
    22  wpgl                                0x00001d44 main + 102
    23  wpgl                                0x00001cd5 start + 53
)
terminate called after throwing an instance of 'NSException'

In my WpglViewController.h file I have the following declared:

@interface WpglViewController : NSObject <UIApplicationDelegate>

{
    UILabel *servingsLabel;
    UILabel *quantityLabel;
    UINavigationController *navigationController;
}

@property (nonatomic, retain) IBOutlet UILabel *servingsLabel;
@property (nonatomic, retain) IBOutlet UILabel *quantityLabel;
@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) UINavigationController *navigationController;

@end

and in my WpglViewController I have the following declared:

#import "WpglViewController.h"

@implementation WpglViewController

@synthesize servingsLabel;
@synthesize quantityLabel;
@synthesize navigationController;

---

WpglViewController needs to be a subclass of UIViewController.

The exception says that WpglViewController doesn't respond to the title method which it expects in a UIViewController.

---

2011-09-04 07:59:49.309 wpgl[7302:207] -[WpglViewController title]: unrecognized selector sent to instance 0x4b134c0

This message says everything: Your WpglViewController does not implement the method "title", maybe you forgot to @synthesize the property in your .m file?

---

Check [WpglViewController title] apparently the problem is here, maybe you are calling this method inside the init of the same class.

---

Make sure your WpglViewController is inherited from UIViewController.

---

either there is no such class as WpglViewController or you havent imported it OR MOST LIKELY you didnt initiliaze it with a nib name. WpglViewController is a class, you have to assign a nib inside initiliazation within another class WpglViewController *firstViewController = [[WpglViewController alloc] initWithNibName:@"the WpglViewController nib name which is probably WpglViewController unless you changed it do not put eh .xib extension"];