iOS Tutorial => Objective-C Associated Objects

Introduction

First introduced in iOS 3.1 as part of the Objective-C runtime, associated objects provide a way to add instance variables to an existing class object (w\o subclassing.

This means you'll be able to attach any object to any other object without subclassing.

Syntax

void objc_setAssociatedObject(id object, void *key, id value, objc_AssociationPolicy policy)
id objc_getAssociatedObject(id object, void *key)
void objc_removeAssociatedObjects(id object)

Parameters

Param	Details
object	The existing object you want to modify
key	This can basically be any pointer that has a constant memory address, but a nice practice is to use here a computed property (getter)
value	The object you want to add
policy	The memory policy for this new `value` i.e. should it be retained / assigned, copied etc.. just like any other property you'd declare