(iOS) Creating custom delegates

1.CustomClass.h

//Class will be declared later
@class CustomClass;

//Define the protocol for the delegate
@protocol CustomClassDelegate

@required
//Required methods go here

//If there are optional functions, they go here
@optional
-(void)sayHello:(CustomClass *)customClass;

@end

//The NSObject protocol contains a method, respondsToSelector:
//that can be used to ensure the delegate object actually implements an optional method before the method is called

@interface CustomClass : NSObject

//Delegate property
@property (nonatomic, weak) IBOutlet  id <CustomClassDelegate> delegate;

// define public functions
-(void)helloDelegate;

@end

2.CustomClass.mm

#import "CustomClass.h"


@implementation CustomClass

@synthesize delegate;

-(id)init {
    self = [super init];
    return self;
}

//Calling this method will cause the sayHello: method to be triggered
-(void)helloDelegate {
    //Verify that the delegate is set and the delegate optional method is implemented (so app won't crash)
    if (delegate != nil && [delegate respondsToSelector:@selector(sayHello:)]){
        [[self delegate] sayHello:self];
    }
}

-(void)dealloc {
    [super dealloc];
}

@end

3.ViewController.h

// import our custom class
#import "CustomClass.h"

@interface ViewController : UIViewController <CustomClassDelegate>

@end

4.ViewController.mm

@implementation ViewController

//Initialization
- (void)viewDidLoad
{
    [super viewDidLoad];

    CustomClass *custom = [[CustomClass alloc] init];
    //Assign delegate
    custom.delegate = self;

    //Calling the helloDelegate will cause the sayHello: to be triggered
    [custom helloDelegate];
}

-(void)dealloc
{
  [custom release];

  [super dealloc];
}

//Implementing the custom delegate function
-(void)sayHello:(CustomClass *)customClass {
    NSLog(@"Hiya!");
}


@end

Click here for set custom delegate and protocol method in swift 4.0