Delegates: Difference between revisions

Classic Objective-C

return 0;

}</lang>

Objective-C 2.0, modern runtime, Automatic Reference Counting, Autosynthesize (LLVM 4.0+)

{{works with|Cocoa}}

<lang objc>#import <Foundation/Foundation.h>

// Formal protocol for the delegate

@protocol DelegatorDelegatingProtocol

- (NSString *)thing;

@end

@interface Delegator : NSObject

@property (weak) id delegate;

- (NSString *)operation;

@end

@implementation Delegator

- (NSString *)operation {

if ([self.delegate respondsToSelector: @selector(thing)])

return [self.delegate thing];

return @"default implementation";

}

@end

@interface Delegate : NSObject

<DelegatorDelegatingProtocol>

@end

@implementation Delegate

- (NSString *)thing { return @"delegate implementation"; }

@end

// Example usage with Automatic Reference Counting

int main() {

@autoreleasepool {

// Without a delegate:

Delegator *a = [Delegator new];

NSLog(@"%@", [a operation]); // prints "default implementation"

// With a delegate that does not implement thing:

a.delegate = @"A delegate may be any object";

NSLog(@"%@", [a operation]); // prints "default implementation"

// With a delegate that implements "thing":

Delegate *d = [Delegate new];

a.delegate = d;

NSLog(@"%@", [a operation]); // prints "delegate implementation"

}