how to extend a protocol for a delegate in objective C, then subclass an object to require a conforming delegate

Question

I want to subclass UITextView, and send a new message to the delegate. So, I want to extend the delegate protocol. What's the correct way to do this?

I started out with this:

interface:

#import <Foundation/Foundation.h>  @class MySubClass;  @protocol MySubClassDelegate <UITextViewDelegate> - (void) MySubClassMessage: (MySubClass *) subclass; @end   @interface MySubClass : UITextView { }  @end 

implementation:

#import "MySubClass.h"   @implementation MySubClass  - (void) SomeMethod; {      if ([self.delegate respondsToSelector: @selector (MySubClassMessage:)]) {          [self.delegate MySubClassMessage: self];     } }  @end 

however with that I get the warning: '-MySubClassMessage:' not found in protocol(s).

I had one way working where I created my own ivar to store the delegate, then also stored the delegate using [super setDelegate] but that seemed wrong. perhaps it's not.

I know I can just pass id's around and get by, but My goal is to make sure that the compiler checks that any delegate supplied to MySubClass conforms to MySubClassDelegate protocol.

To further clairfy:

@interface MySubClassTester : NSObject {  }  @implementation MySubClassTester  - (void) one {      MySubClass *subclass = [[MySubClass alloc] init];     subclass.delegate = self; }  @end 

will produce the warning: class 'MySubClassTester' does not implement the 'UITextViewDelegate' protocol

I want it to produce the warning about not implementing 'MySubClassDelegate' protocol instead.

Answer 1

The UITextView defines its delegate as

@property(nonatomic, assign) id<UITextViewDelegate> delegate 

meaning it conforms to UITextViewDelegate, and that's what compiler checks. If you want to use the new protocol, you need to redefine delegate to conform to your protocol:

@interface MySubClass : UITextView { } @property(nonatomic, assign) id<MySubClassDelegate> delegate    @end 

The compiler shouldn't give any more warnings.

[Update by fess]

... With this the compiler will warn that the accessors need to be implemented... [I implemented this:]

-(void) setDelegate:(id<MySubClassDelegate>) delegate { [super setDelegate: delegate]; } - (id) delegate { return [super delegate]; } 

"

[My update]

I believe it should work if you only make a @dynamic declaration instead of reimplementing the method, as the implementation is already there:

@dynamic delegate; 

Answer 2

For anyone still interested, this can be done quite simply like this (for sake of the example, I subclass UIScrollView):

@protocol MySubclassProtocol <UIScrollViewDelegate> @required -(void)myProtocolMethod; @end  @interface MySubClass : UIScrollView  @property (nonatomic, weak) id <MySubclassProtocol> delegate; 

The most important detail here is the part between the <> after your protocol's name which, put in a simple manner, signals you're extending that protocol. In your implementation, all you need to do then is:

@synthesize delegate; 

And you're done.