Objective-c – How to use custom delegates in Objective-C


I need to know about the usage of delegate methods in Objective-C. Can anyone point me to the correct source?

Best Solution

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:

@class Foo;
@protocol FooDelegate <NSObject>
- (BOOL)foo:(Foo *)foo willDoSomethingAnimated:(BOOL)flag;
- (void)foo:(Foo *)foo didDoSomethingAnimated:(BOOL)flag;

@interface Foo : NSObject {
     NSString *bar;
     id <FooDelegate> delegate;

@property (nonatomic, retain) NSString *bar;
@property (nonatomic, assign) id <FooDelegate> delegate;

- (void)someAction;


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 under FooDelegate (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 this Foo object to have its delegate property set:

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.