How do I create delegates in Objective-C?

Question

I know how delegates work, and I know how I can use them.

But how do I create them?

Answer 1

Ok, this is not really an answer to the question, but if you are looking up how to make your own delegate maybe something far simpler could be a better answer for you.

I hardly implement my delegates because I rarely need. I can have ONLY ONE delegate for a delegate object. So if you want your delegate for one way communication/passing data than you are much better of with notifications.

NSNotification can pass objects to more than one recipients and it is very easy to use. It works like this:

MyClass.m file should look like this

#import "MyClass.h"
@implementation MyClass 

- (void) myMethodToDoStuff {
//this will post a notification with myClassData (NSArray in this case)  in its userInfo dict and self as an object
[[NSNotificationCenter defaultCenter] postNotificationName:@"myClassUpdatedData"
                                                    object:self
                                                  userInfo:[NSDictionary dictionaryWithObject:selectedLocation[@"myClassData"] forKey:@"myClassData"]];
}
@end

To use your notification in another classes: Add class as an observer:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(otherClassUpdatedItsData:) name:@"myClassUpdatedData" object:nil];

Implement the selector:

- (void) otherClassUpdatedItsData:(NSNotification *)note {
    NSLog(@"*** Other class updated its data ***");
    MyClass *otherClass = [note object];  //the object itself, you can call back any selector if you want
    NSArray *otherClassData = [note userInfo][@"myClassData"]; //get myClass data object and do whatever you want with it
}

Don't forget to remove your class as an observer if

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}