Properly declare delegation in Objective C (iPhone) - iphone

Question

Ok, This has been explained a few times (I got most of the way there using this post on SO), but I am missing something. I am able to compile cleanly, and able to set the delegate as well as call methods from the delegate, but I'm getting a warning on build:
No definition of protocol 'DetailViewControllerDelegate' is found
I have a DetailViewController and a RootViewController only. I am calling a method in RootViewController from DetailViewController. I have the delegate set up as so:
In RootViewController.h:
#import "DetailViewController.h"
#interface RootViewController : UITableViewController <NSFetchedResultsControllerDelegate, DetailViewControllerDelegate> //Error shows up here
{
//Some Stuff Here
}
//Some other stuff here
#end
In RootViewController.m I define the delegate when I create the view using detailViewController.delegate = self
In DetailViewController.h:
#protocol DetailViewControllerDelegate;
#import "RootViewController.h"
#interface DetailViewController : UITableViewController <UITextFieldDelegate>
{
id <DetailViewControllerDelegate> delegate;
}
#property (nonatomic, assign) id <DetailViewControllerDelegate> delegate;
#end
#protocol DetailViewControllerDelegate
//some methods that reside in RootViewController.m
#end
I feel weird about declaring the protocol above the import in DetailViewController.h, but if I don't it doesn't build. Like I said, the methods are called fine, and there are no other errors going on. What am I missing here?

Answer 1

pheelicks is pretty much there but it looks like some of your protocol methods also use the DetailViewController class, I imagine it looks something like this :
#protocol DetailViewControllerDelegate <NSObject>
- (void) controller:(DetailViewController *)controller hasSomething:(id)thing;
#end
#class DetailViewController : UITableViewController <UITextFieldDelegate> {
id <DetailViewControllerDelegate> delegate;
}
#property (nonatomic, assign) id <DetailViewControllerDelegate> delegate;
#end
and you haven't defined DetailViewController yet so you will get an error in the protocol definition.
You can fix this in two ways :
a) Declare (but don't define yet) the class before the protocol
#class DetailViewController;
#protocol DetailViewControllerDelegate <NSObject>
- (void) controller:(DetailViewController *)controller hasSomething:(id)thing;
#end
b) Just use UITableViewController instead of DetailViewController in your protocol methods.
#protocol DetailViewControllerDelegate <NSObject>
- (void) controller:(UITableViewController *)controller hasSomething:(id)thing;
#end
Personally, I choose solution (a) but it really depends on what you're trying to do.
Hope that helps.

Answer 2

Try:
In DetailViewController.h:
#import "RootViewController.h"
#protocol DetailViewControllerDelegate <NSObject>
//some methods that reside in RootViewController.m
#end
#interface DetailViewController : UITableViewController <UITextFieldDelegate>
{
id <DetailViewControllerDelegate> delegate;
}
#property (nonatomic, assign) id <DetailViewControllerDelegate> delegate;
#end

Answer 3

Here is another way that you could tackle this, similar to the solution proposed by deanWombourne.
#protocol DetailViewControllerDelegate;
#interface DetailViewController : UITableViewController <UITextFieldDelegate> {
id <DetailViewControllerDelegate> delegate;
}
#property (nonatomic, assign) id <DetailViewControllerDelegate> delegate;
#end
#protocol DetailViewControllerDelegate <NSObject>
- (void) controller:(DetailViewController *)controller hasSomething:(id)thing;
#end