"Incomplete implementation" warning in XCode 4.0 - objective-c

Question

This application is rewritten code from the Cococa and Objective C Up and Running book.
As I try to understand everything in the beginning, I would like to know, where I made a mistake, in the code below. To me, everything looks fine.
Could you, therefore, help me identify the source of the warning:
Incomplete Implementation
I got this in the #implementation Photo line in Photo.m source code file?
Photo.h
#import <Foundation/Foundation.h>
#interface Photo : NSObject{
NSString* caption;
NSString* photographer;
}
+ (Photo*) photo;
- (NSString*) caption;
- (NSString*) photographer;
- (void) setCaption: (NSString*)input;
- (void) setPhotographer: (NSString*)input;
#end
Photo.m
#import "Photo.h"
#implementation Photo // <- Incomplete Implementation?
- (id)init
{
self = [super init];
if (self) {
[self setCaption:#"Default Caption"];
[self setPhotographer:#"Default Photographer"];
}
return self;
}
+ (Photo*) caption {
Photo* newPhoto = [[Photo alloc] init];
return [newPhoto autorelease];
}
- (NSString*) caption {
return caption;
}
- (NSString*) photographer {
return photographer;
}
- (void) setCaption:(NSString *)input {
[caption autorelease];
caption = [input retain];
}
- (void) setPhotographer: (NSString *)input {
[photographer autorelease];
photographer = [input retain];
}
- (void)dealloc
{
[self setCaption:nil];
[self setPhotographer:nil];
[super dealloc];
}
#end
I use Snow Leopard 10.6.7 and Xcode 4.0.0.

Answer 1

Unless its a typo, your Class method defined as + (Photo*) Photo; is not implemented (there is a + (Photo*) Caption {} method which looks its just an accident.
Edit: A simpler way to do have this functionality is to use properties, which are a shortcut that create the getter and setter for a variable for us, (see this link for a good beginner's tutorial: iPhone 101) for your instance variables like so:
in your .h file:
#interface Photo : NSObject{
NSString* caption;
NSString* photographer;
}
#property (nonatomic, retain) NSString *caption;
#property (nonatomic, retain) NSString *photographer;
#end
in your .m file:
#implementation Photo
#synthesize caption, photographer;
//Other stuff (init and any custom methods for class etc.. NOT getters and setters for variables)
- (void)dealloc
{
[caption release];
[photographer release];
[super dealloc];
}

Answer 2

You are receiving this error because in your header file you declared that there would be a method:
+ (Photo*) photo;
but you didn't implement it in the m file.
EDIT:
It looks like this:
+ (Photo*) caption {
Photo* newPhoto = [[Photo alloc] init];
return [newPhoto autorelease];
}
should be:
+ (Photo*) photo {
Photo* newPhoto = [[Photo alloc] init];
return [newPhoto autorelease];
}

Answer 3

In general, when you mouse over the warning, it will not tell you which method it is missing, but there are at least two other ways to get this information:
Type Cmd-4 or select the Issue Navigator view (the ! in a triangle icon), then expand the "Semantic Issue" warning for this issue. You will then see a message to the effect of "Method definition for "" not found.
Type Cmd-7 or select the Log View (the rightmost icon that looks like a caption bubble), then select the appropriate issue from the list. You will see the same message.

Answer 4

You are missing +photo because you accidentally typed caption:
+ (Photo*) caption {
Photo* newPhoto = [[Photo alloc] init];
return [newPhoto autorelease];
}
should be
+ (Photo*) photo {
Photo* newPhoto = [[Photo alloc] init];
return [newPhoto autorelease];
}

Answer 5

Your .m file does not have the implementation for:
+ (Photo*) photo;
That's the missing method.

Answer 6

try changing
+ (Photo*) caption {
Photo* newPhoto = [[Photo alloc] init];
return [newPhoto autorelease];
}
to
+ (Photo*) photo {
Photo* newPhoto = [[Photo alloc] init];
return [newPhoto autorelease];
}