How to use custom delegates in Objective-C

You will want to declare a delegate protocol for your class. An example of a delegate protocol and interface for class Foo might look like this:

view plain
@class Foo;  
@protocol FooDelegate <NSObject>  
@optional  
- (BOOL)foo:(Foo *)foo willDoSomethingAnimated:(BOOL)flag;  
- (void)foo:(Foo *)foo didDoSomethingAnimated:(BOOL)flag;  
@end  
@interface Foo : NSObject {  
     NSString *bar;  
     id <FooDelegate> delegate;  
}  
  
@property (nonatomic, retain) NSString *bar;  
@property (nonatomic, assign) id <FooDelegate> delegate;  
  
- (void)someAction;  
  
@end  

Don't forget to synthesize your properties in the @implementation.

What this code did was declare a protocol called FooDelegate; a class that conforms to this protocol would be declared like @interface SomeClass : SuperClass <FooDelegate> {}. Because this class conforms to the protocol FooDelegate, it now gets to implement the methods underFooDelegate (to require that these be implemented, use @required instead of @optional). The last step is for a Foo object to be instantiated in the class that conforms to FooDelegate, and for thisFoo object to have its delegate property set:

view plain
Foo *obj = [[Foo alloc] init];  
[obj setDelegate:self];  

Now, your class is prepared to receive messages from Foo objects that have their delegates set correctly.