init with delegate protocol

Question

Whenever I create an init that has a delegate conforming to a protocol I write the init as this:

- (id)initWithDelegate:(id<ProtocolToConform>)delegate;

This way I will have a warning if the creating object does not conform to the protocol.

However I noticed that ie UIAlertView init method looks like this:

- (id)initWithTitle:(NSString *)title message:(NSString *)message delegate:(id)delegate cancelButtonTitle:(NSString *)cancelButtonTitle otherButtonTitles:(NSString *)otherButtonTitles, ...

The delegate argument does not specify to conform to the UIAlertViewDelegate protocol? Any clues why Apple has done it that way?

Answer 1

Good question! I do the same thing in the hope of catching more errors at compile time.

Apple appear to be conforming to their own standards; as stated in Concepts in Objective-C:

To implement a delegate for your custom class, complete the following steps:

Declare the delegate accessor methods in your class header file.

- (id)delegate;
- (void)setDelegate:(id)newDelegate;

Implement the accessor methods. In a memory-managed program, to avoid retain cycles, the setter method should not retain or copy your delegate.

- (id)delegate {
    return delegate;
}
 
- (void)setDelegate:(id)newDelegate {
    delegate = newDelegate;
}