Custom Delegate cannot find declaration

Question

I'm creating a shopping list app, and trying to implement a custom delegate when editing an item. When creating the @protocol at the bottom of the header file, when trying to declare a property of that protocol in the @interface section I'm getting an error of: Cannot find protocol declaration for GEMEditItemViewControllerDelegate

This is what my header file looks like.

#import <UIKit/UIKit.h>
#import "GEMItem.h"

@interface GEMEditItemViewController : UIViewController <UIPickerViewDataSource, UIPickerViewDelegate>

@property GEMItem *item;
@property (weak) id<GEMEditItemViewControllerDelegate> delegate;

@end

@protocol GEMEditItemViewControllerDelegate <NSObject>
@required
- (void)controller:(GEMEditItemViewController *)controller didUpdateItem:(GEMItem *)item;
@end // End of delegate protocol

Alternatively in a separate instance when declaring the protocol above the interface I cannot access the view controller to pass as a parameter for that declaration method.

That header file looks like:

#import <UIKit/UIKit.h>
#import "GEMItemManager.h"

@protocol GEMAddItemViewControllerDelegate <NSObject>
/*
// Tried to add the controller (controller:(GEMAddItemviewController *)controller) as first paramiter, but was getting and errror, so I have omitted it for the time being
- (void)controller:(GEMAddItemViewController *)controller didSaveItemWithName:(NSString *)name andQuantity:(float)quantity andPrice:(float)price andCategory:(NSString *)category andNotes:(NSString *)notes;
*/

- (void)didSaveItemWithName:(NSString *)name andQuantity:(float)quantity andPrice:(float)price andCategory:(NSString *)category andNotes:(NSString *)notes;

@end

@interface GEMAddItemViewController : UIViewController <UIPickerViewDataSource, UIPickerViewDelegate>

@property (weak) id<GEMAddItemViewControllerDelegate> delegate;

@property NSArray *categories;

@end

Any thoughts on how to correct this would be greatly appreciated!!

Answer 1

You can do it like this also

@protocol GEMEditItemViewControllerDelegate;
@interface GEMEditItemViewController : UIViewController <UIPickerViewDataSource, UIPickerViewDelegate>

@property GEMItem *item;
@property (weak) id<GEMEditItemViewControllerDelegate> delegate;

@end

@protocol GEMEditItemViewControllerDelegate <NSObject>
@required
- (void)controller:(GEMEditItemViewController *)controller didUpdateItem:(GEMItem *)item;
@end

Answer 2

Try it this way:

@class GEMEditItemViewController; // forward declaration of class

@protocol GEMEditItemViewControllerDelegate <NSObject>
@required
- (void)controller:(GEMEditItemViewController *)controller didUpdateItem:(GEMItem *)item;
@end // End of delegate protocol

@interface GEMEditItemViewController : UIViewController <UIPickerViewDataSource, UIPickerViewDelegate>

@property GEMItem *item;
@property (weak) id<GEMEditItemViewControllerDelegate> delegate;

@end

BTW - you should move the two picker view protocols from the header file to a class extension in the .m file. The world doesn't need to know this implementation detail.

Answer 3

Your header file should looks like this:

@class GEMEditItemViewController;
@class GEMItem;

@protocol GEMEditItemViewControllerDelegate <NSObject>
@required
- (void)controller:(GEMEditItemViewController *)controller didUpdateItem:(GEMItem *)item;
@end // End of delegate protocol

@interface GEMEditItemViewController : UIViewController <UIPickerViewDataSource, UIPickerViewDelegate>

@property GEMItem *item;
@property (weak) id<GEMEditItemViewControllerDelegate> delegate;

@end

You should not use direct import in your header file. @class directive is used to prevent cycle dependencies. In your case GEMItem import should be in your meta file.