Confused about addTarget pointer behavior for addTarget:action:forControlEvents: - ios

Question

I have a UIView subclass with a delegate property. In the init method, I set
self.delegate = nil.
The view also has a button, so in the init method, I also set the target of the button to be self.delegate, which is nil:
[myButton addTarget:self.delegate action:#selector(buttonAction) forControlEvents:UIControlEventTouchUpInside]
In the UIViewController that sets up my UIView subclass, I call a method in the UIView that sets the UIView's self.delegate to the UIViewController. When I click the button, the change in target seems to be reflected.
I am wondering how this ends up working, as my understanding is that addTarget:action:forControlEvents takes an id as the target, and pointers should be pass by value in Obj-C. Thus, I am pretty confused about why the originally nil-valued pointer was updated after the addTarget method was already called.

Answer 1

The right way to do that is declaring a protocol for your view, which will delegate for button's tap action, i.e.
YourView.h
#class YourView;
#protocol YourViewDelegate
#optional
- (void)customView:(YourView *)view didSelectButton:(id)button;
#end
#interface YourView : UIView
//...
#property (weak, nonatomic) id <YourViewDelegate> delegate;
#end
YourView.m
#interface YourView()
#end
#implementation
- (id)init
{
if (self = [super init]) {
//...
[self setup];
}
return self;
}
- (void)awakeFromNib
{
//...
// setup logic when this view created from storyboard
[self setup];
}
- (void)setup
{
[myButton addTarget:self
action:#selector(buttonTapped:)
forControlEvents:UIControlEventTouchUpInside];
}
- (void)buttonTapped:(id)sender
{
if (self.delegate && [self.delegate respondsToSelector:#selector(customVIew:didSelectButton)] {
[self.delegate customView:self didSelectButton:sender];
}
}
#end
Then, in your view controller implement YourViewDelegate category:
#interface YourViewController()
//...
#end
#implementation
- (void)viewDidLoad
{
[super viewDidLoad];
//...
self.yourView.delegate = self;
}
//...
- (void)customView:(YourView *)view didSelectButton:(id)button
{
//do your stuff
}
#end

Answer 2

Objective-C uses Dynamic binding. Method to invoke is determined at runtime instead of at compile time. Which is why it is also referred to as late binding.
Reference link -
https://developer.apple.com/library/ios/documentation/general/conceptual/DevPedia-CocoaCore/DynamicBinding.html
So what will be the delegate and which method is being called is defined at runtime.