How to use custom delegates in Objective-C

cocoa-touch, delegates, objective-c

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>
@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 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.

Problem

Original source