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

Here is a simple method to create delegates

Create Protocol in .h file. Make sure that is defined before the protocol using @class followed by the name of the UIViewController < As the protocol I am going to use is UIViewController class>.

Step : 1 : Create a new class Protocol named "YourViewController" which will be the subclass of UIViewController class and assign this class to the second ViewController.

Step : 2 : Go to the "YourViewController" file and modify it as below:

#import 
@class YourViewController;

@protocol YourViewController Delegate 

 @optional
-(void)defineDelegateMethodName: (YourViewController *) controller;

@required
-(BOOL)delegateMethodReturningBool: (YourViewController *) controller;

  @end
  @interface YourViewController : UIViewController

  //Since the property for the protocol could be of any class, then it will be marked as a type of id.

  @property (nonatomic, weak) id< YourViewController Delegate> delegate;

@end

The methods defined in the protocol behavior can be controlled with @optional and @required as part of the protocol definition.

Step : 3 : Implementation of Delegate

    #import "delegate.h"

   @interface YourDelegateUser ()
     
   @end

   @implementation YourDelegateUser

   - (void) variousFoo {
      YourViewController *controller = [[YourViewController alloc] init];
      controller.delegate = self;
   }

   -(void)defineDelegateMethodName: (YourViewController *) controller {
      // handle the delegate being called here
   }

   -(BOOL)delegateMethodReturningBool: (YourViewController *) controller {
      // handle the delegate being called here
      return YES;
   }

   @end

//test whether the method has been defined before you call it

 - (void) someMethodToCallDelegate {
     if ([[self delegate] respondsToSelector:@selector(defineDelegateMethodName:)]) {
           [self.delegate delegateMethodName:self]; 
     }
  }