Declare protocol before defining it?

I was looking at ways to declare a protocol without defining, if such a thing makes sense. By declare I mean somehow telling the compiler the name of a protocol only, without defining the methods that should be adopted. This is similar to @class for classes,

@class MyClass;

The reason I wanted to do so was because I had a header file that looked like this,

@interface MyClass {
 id mDelegate;
}
@property (nonatomic, retain) id mDelegate;

@end

@protocol MyDelegateProtocol
- (void) doStuff;
@end

This works fine. However, I don’t like the following because I’m not being specific on the type for mDelegate,

id mDelegate;

Being a Java programmer, I instinctively tried MyDelegateProtocol* mDelegate, which doesn’t work. The solution is to move the protocol definition before the interface declaration and use id<MyDelegateProtocol>,

@protocol MyDelegateProtocol
- (void) doStuff;
@end

@interface MyClass {
 id<MyDelegateProtocol> mDelegate;
}
@property (nonatomic, retain) id<MyDelegateProtocol> mDelegate;

@end

I then got the error

-release not found in protocol(s)

Inheriting from NSObject did the trick,

@protocol MyDelegateProtocol <NSObject>

Posted in: Objective C, Uncategorized

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