No visible @interface for 'AppDelegate' declares the selector 'displayMessage'

Question

i'm following a tutorial from this book:

http://books.google.co.uk/books?id=6WtVAQAAQBAJ&pg=PA569&lpg=PA569&dq=%5Bself+displayMessage:+kDenied%5D&source=bl&ots=PSj5Nu_QyI&sig=VHOeJtYHARgMOqSEdREyCtcgxc8&hl=en&sa=X&ei=b2rxUv-iN4WQhQfwxIGYDQ&ved=0CC0Q6AEwAA#v=onepage&q=%5Bself%20displayMessage%3A%20kDenied%5D&f=false

But when I put this code into AppDelegate.m I get the error message "No visible @interface for 'AppDelegate' declares the selector 'displayMessage'", however i'm following the code as it is written.

CFErrorRef error = NULL;

switch (ABAddressBookGetAuthorizationStatus()) {
    case kABAuthorizationStatusAuthorized:{
        addressBook = ABAddressBookCreateWithOptions(NULL, &error);
        [ self useAddressBook:addressBook];
        // Do you work and once your finished..
        if (addressBook != NULL) {
            CFRelease(addressBook);
        }
        break;
    }
    case kABAuthorizationStatusDenied:{
        [self displayMessage: kDenied];
        break;
    }
    case kABAuthorizationStatusNotDetermined:{
        addressBook = ABAddressBookCreateWithOptions(NULL, &error);
        ABAddressBookRequestAccessWithCompletion
        (addressBook, ^(BOOL granted, CFErrorRef error)
        {
            if (granted){
                NSLog(@"Access was granted");
                [self useAddressBook:addressBook];
            } else {
                NSLog(@"Access was not granted");
            }
            if (addressBook != NULL){
                CFRelease(addressBook);
            }
        });
        break;
    }
    case kABAuthorizationStatusRestricted:{
        [self displayMessage: kRestricted];
        break;
    }
}

self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];
return YES;

}

Answer 1

You're calling the following instance method:

[self displayMessage: kRestricted];

Which isn't declared in your subclass of UIApplication (AppDelegate).

To solve this, just implement the displayMessage: method:

- (void)displayMessage:(id)message
{
    // do stuff here
}

Answer 2

The message is telling you that you are calling the method displayMessage: and you have not defined it.

Your book is using this method in section 13.1 but there is no definition of it in that section, however what looks like a suitable definition can be found in section 19.1. That definition displays a string in an alert.

HTH

Addendum

The full source of all the examples in the book is available for download from GitHub . The author's definition of your missing method is:

- (void) displayMessage:(NSString *)paramMessage
{
    [[[UIAlertView alloc] initWithTitle:nil
                                message:paramMessage
                               delegate:nil
                      cancelButtonTitle:@"OK"
                      otherButtonTitles:nil] show];
}

You might want to download the full archive as it looks like other examples may be incomplete as well.