No type or protocol named

问题

After searching of an the answer to this I found many related questions but after implementing them I am still unable to get rid of this error.
I've a class which is of AFHTTPRequestOperationManager type. In this class .h file right after the Import statements end I have written @protocol apiClientDelegate; and in the @interface there is a @property (weak) id<apiClientDelegate>delegate; and after it @end I've written:

@protocol apiClientDelegate <NSObject>
@required
-(void)finalImageURLs:(NSMutableArray*)array;
@end

So in another class which is a UICollectionViewController I've written it as @interface GalleryCollectionViewController : UICollectionViewController <apiClientDelegate> and it is still showing this error. Here are the screenshots: and in the class where it is giving the error:

UPDATE
After one of the comment I added @protocol apiClientDelegate; in the GalleryCOllectionViewController but now it started showing this warning and the method is not bein executed:

来源：https://stackoverflow.com/questions/36827903/no-type-or-protocol-named