Associated objects inUIAlertView in iOS - ios

Question

Associated objects are used for creating property in iOS and some cunning changes in iOS. Would anyone care to explain how is this doing any of these?
- (IBAction)doSomething:(id)sender {
UIAlertView *alert = [[UIAlertView alloc]
initWithTitle:#"Alert" message:nil
delegate:self
cancelButtonTitle:#"OK"
otherButtonTitles:nil];
objc_setAssociatedObject(alert, &kRepresentedObject,
sender,
OBJC_ASSOCIATION_RETAIN_NONATOMIC);
[alert show];
}
- (void)alertView:(UIAlertView *)alertView
clickedButtonAtIndex:(NSInteger)buttonIndex {
UIButton *sender = objc_getAssociatedObject(alertView,
&kRepresentedObject);
self.buttonLabel.text = [[sender titleLabel] text];
}
The apple's definition does not help me understand either. "Sets an associated value for a given object using a given key and association policy."

Answer 1

As per my knowledge you can that we can add new property at runtime in existing class object.It allow objects to associate arbitrary values for keys at runtime.
Associated Objects—or Associative References, as they were originally
known—are a feature of the Objective-C 2.0 runtime, introduced in OS X
Snow Leopard (available in iOS 4). The term refers to the following
three C functions declared in , which allow objects to
associate arbitrary values for keys at runtime:
objc_setAssociatedObject
objc_getAssociatedObject
objc_removeAssociatedObjects
Why we use this ? as its allow us to add custom property to existing class and can utilize where it required and after that we will remove that property at runtime.
As per your Usage here you can say that there is no sender property in UIAlertView class and you haven't rights to change UIAlertView so by the use of associateObject you can add run time property which you needed while alert delegate will call.
objc_setAssociatedObject(alert, &kRepresentedObject,
sender,
OBJC_ASSOCIATION_RETAIN_NONATOMIC);
This will add it runtime and we can also remove it after its usage at runtime.
You can find more detail on this link : AssociatedObject
Hope this will helps to understand AssociatedObject concept at runtime.