Objective-C protocol and Delegation

Objective-C ProtocolAndDelegateThis is the content to be introduced in this article.Objective-CMediumProtocolAndDelegateThrough examples, we can learn more quickly and conveniently.Objective-CFirst, let's look at the details.

Protocol-ProtocolThat is, after using this agreement, we must follow this agreement, and the methods required by the Agreement must be implemented.

Delegate-DelegateAs the name suggests, it is to entrust others to do things, that is, when one thing happens, they will not handle it themselves and let others handle it.

When A view contains B view

B view needs to modify the view interface, so delegation is required at this time.

Several steps are required

1. First define an agreement

2. Methods of a view Implementation Protocol

3. B view sets a delegate variable.

4. Set the delegate variable of B view to a view, which means that B view delegates a view to do things.

5. After an event occurs, use the delegate variable to call the Protocol method in a view.

Example:

 
 

  
  
B _View.h:
  
  
@ Protocol UIBViewDelegate <NSObject>
  
  
@ Optional
  
  
-(Void) ontouch :( UIScrollView *) scrollView; // declares the Protocol method.
  
  
@ End
  
  
 
  
  
@ Interface BView: UIScrollView <UIScrollViewDelegate>
  
  
{
  
  
Id <UIBViewDelegate> _ touchdelegate; // sets the delegate variable.
  
  
}
  
  
@ Property (nonatomic, assign) id <UIBViewDelegate> _ touchdelegate;
  
  
@ End
  
  
 
  
  
B _View.mm:
  
  
 
  
  
@ Synthesize _ touchdelegate;
  
  
-(Id) initWithFrame :( CGRect) frame {
  
  
If (self = [super initWithFrame: frame]) {
  
  
// Initialization code
  
  
_ Touchdelegate = nil;
  
  
}
  
  
Return self;
  
  
}
  
  
 
  
  
-(Void) touchesBegan :( NSSet *) touches withEvent :( UIEvent *) event
  
  
{
  
  
[Super touchesBegan: touches withEvent: event];
  
  
If (_ touchdelegate! = Nil & [_ touchdelegate respondsToSelector: @ selector (ontouch :)] = true)
  
  
[_ Touchdelegate ontouch: self]; // call protocol delegate
  
  
}
  
  
@ End
  
  
 
  
  
A_View.h:
  
  
 
  
  
@ Interface AViewController: UIViewController <UIBViewDelegate>
  
  
{
  
  
BView * m_BView;
  
  
}
  
  
@ End
  
  
 
  
  
A_View.mm:
  
  
 
  
  
-(Void) viewWillAppear :( BOOL) animated
  
  
{
  
  
M_BView. _ touchdelegate = self; // sets the delegate
  
  
[Self. view addSubview: m_BView];
  
  
}
  
  
 
  
  
-(Void) ontouch :( UIScrollView *) scrollView
  
  
{
  
  
// Implementation Protocol
  
  
}
 
 

Summary:Objective-C ProtocolAndDelegateI hope this article will help you!