CODEWITHSUNDEEP
objective-cuikitprotocols
ma11hew28
ma11hew28

Reputation: 126507

Does simply conforming to an Objective-C protocol do anything?

CocoaPlant defines a protocol CPCoreDataTraits, analogous to UITexInputTraits like so:

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

@protocol CPCoreDataTraits <NSFetchedResultsControllerDelegate>

@optional

@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (strong, nonatomic) NSFetchedResultsController *fetchedResultsController;

@end

If I only want to synthesize the managedObjectContext property for one of my view controllers,

@implementation MyViewController
@synthesize managedObjectContext;
@end

i.e., I don't want to synthesize the fetchedResultsController property or implement any of the NSFetchedResultsControllerDelegate methods, should I still conform to the CPCoreDataTraits protocol, like so?

@interface MyViewController : UIViewController <CPCoreDataTraits>
@end

I.e., as long as I don't synthesize the fetchedResultsController property or implement any of the NSFetechedResultsControllerDelegate methods, then will the end result be exactly as if I had just declared the managedObjectContext property normally, like so?

@interface MyViewController : UIViewController
@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@end

Upvotes: 0

Views: 125

Answers (1)

viggio24
viggio24

Reputation: 12366

As you can see in the protocol declaration, the implementation by your class of the two properties is optional because these two properties have been declared under the @optional statement. This means that any other class that will use any object conforming to this protocol, must check the effective implementation of an optional method or property before using it.

In the example, any class that wants to access the fetchedResultsController property has to check for the existence of the getter and/or setter methods, e.g. using the: 


[myController respondsToSelector:@selector(fetchedResultsController)];
[myController respondsToSelector:@selector(setFetchedResultsController:)];

If the calling method doesn't do this preliminary check and your protocol implementation doesn't support any of these methods (because optional) then the app will raise an exception. So your approach is correct, the only difference in the two examples is that if you don't use the notation than any call to conformsToProtocol: on your object will return NO.

Upvotes: 3

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