Where to set delegate = self? Or should I just use a different design pattern?

Question

EDIT: edited for clarity

Disclaimer: I'm new and pretty bad. But I have tried very hard and read lots of stuff to figure this out, but I have not...

I think my whole delegate pattern would work, except I can't figure out how to set the delegate property of ViewController to self in the MatchLetter class. The reason is because I can't figure out how to call code there. It's not a view controller, so viewDidLoad or prepareForSegue won't work.

This is what I've got:

ViewController.h

#import <UIKit/UIKit.h>

@class ViewController;
@protocol letterMatchProtocol <NSObject>
- (BOOL) isLetterMatch:(char) firstLetter;
@end

@interface ViewController : UIViewController
@property (nonatomic, weak) id <letterMatchProtocol> delegate;
@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

char c = 'a';

// This is the method I want to delegate to MatchLetter, to have a BOOL returned
BOOL returnValue = [self.delegate isLetterMatch:c];
}

@end

MatchLetter.h

#import <Foundation/Foundation.h>
#import "ViewController.h"

@interface Delegate : NSObject <letterMatchProtocol>
@end

MatchLetter.m

#import "MatchLetter.h"

@implementation Delegate

// this is the code I think I need to run here, to set the delegate property...

// ViewController *viewController = [ViewController new];
// viewController.delegate = self;

// ... so that isLetterMatch can be run here from ViewController.m
// But I don't know where to put this code, or how to get it to run before the ViewController
// especially since there are no segues or views to load.

- (BOOL) isLetterMatch:(char)firstLetter {

if (firstLetter == 'a') {
    return YES;
}
else {
        return NO;
    }
}

@end

Can somebody please tell me the best way to proceed? Thanks for reading

Answer 1

You asked "Where to set delegate = self? Or should I just use a different design pattern?".

Answer: Don't. An object should never be it's own delegate.

Your code is quite a mess.

Don't name a class "Delegate". A delegate is a design pattern. The whole point of a delegate is that any object that conforms to a particular protocol ("speaks the language") can serve as the delegate. You don't need to know what class of object is serving as the delegate, but only that it speaks the language you need.

An analogy: When you call the operator, you don't care who is working the operator desk. You don't care about his/her gender, religion, ethnic background, how tall they are, etc. You just care that they speak your language.

Likewise, when you set up a delegate, it doesn't matter what type of object gets set as the delegate. All that matters is that the object that is the delegate conforms to the protocol for that delegate.

A table view can have ANY object serve as it's delegate, as long as that object conforms to the UITableViewDelegate protocol. You usually make you view controller be the table view's delegate, but you don't have to. You could create a custom class that manages your table views, and have it be the delegate. There is no "TableViewDelegate" object class. There is instead a UITableViewDelegate protocol, and any object that conforms to the protocol can act as a table view's delegate.

Edit: Your question is confusing. I think what you're proposing is that your Delegate class would create a view controller and make itself the delegate for the view controller.

If that's what you are talking about, your thinking is backwards. The view controller is using the Delegate class as a helper class. Any given instance of a view controller class can create an instance of the Delegate class and set it as it's delegate if it desires. You might have 3 instances of ViewController at one time, each with it's own instance of your Delegate class.

Thus, the ViewController object is the one that should create and set up an instance of Delegate if it needs one:

- (void) viewDidLoad;
{
  self.delegate = [[Delegate alloc] init];
  //other setup here
}