Question

After setting up the following protocol, I have noticed that I am getting a warning when I try and access properties from the object:

// PROTOCOL
@protocol PetProtocol <NSObject>
- (void)printType;
@end

// CLASS
#import "PetProtocol.h"

@interface Animal : NSObject <PetProtocol> {
    NSString *type;
}
@property (nonatomic, copy) NSString *type;
@end

The following is from a ViewController/viewDidLoad which I am using for testing.

// WARNING: setType not found in protocol
id <PetProtocol> pet_001 = [[Animal alloc] init];
[pet_001 setType:@"DOG"];
[pet_001 printType];

I think I can see why I am getting this warning as neither “id” nor “PetProtocol” define the “type” property. I have two solutions, but I just wanted to check I am getting this right. I am leaning towards 001 as using id and then casting before accessing the method seems like the better option, would anyone care to comment?

// 001
id <PetProtocol> pet_002 = [[Animal alloc] init];
[(Animal *)pet_002 setType:@"DOG"];
[pet_002 printType];

// 002
Animal <PetProtocol> *pet_003 = [[Animal alloc] init];
[pet_003 setType:@"CAT"];
[pet_003 printType];

EDIT:

I have just been looking at this and it seems to work better (i.e. no warning) without adding the protocol after the id?

// 003
id pet_002 = [[Animal alloc] init];
[pet_002 setType:@"HAMSTER"];
[pet_002 printType];

much appreciated

gary.

Answer 1

You need to add getter & setter to the protocol also (not only the class):

// PROTOCOL
@protocol PetProtocol <NSObject>
- (void)printType;
- (void)setType:(NSString*)val;
- (NSString*)type;
@end