How do delegates work in objective c? - ios

Question

I'm trying to figure out delegates because I really need them for a project I'm working on, but for the life of me, I can't figure them out. No matter how much I tweak the code, nothing works
ViewController.h:
#import <UIKit/UIKit.h>
#class ViewController;
#protocol testDelegate
-(void)sayHi;
#end
#interface ViewController : UIViewController
- (IBAction)button:(id)sender;
#property (weak, nonatomic)id <testDelegate> delegate;
#end
ViewController.m:
#import "ViewController.h"
#import "DelegateController.h"
#interface ViewController ()
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
DelegateController *dc = [[DelegateController alloc] init];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (IBAction)button:(id)sender {
[self.delegate sayHi];
}
#end
DelegateController.h:
#import "ViewController.h"
#interface DelegateController : UIViewController <testDelegate>
#end
DelegateController.m:
#import "DelegateController.h"
#interface DelegateController ()
#end
#implementation DelegateController
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
NSLog(#"init");
ViewController *vc = [[ViewController alloc] init];
[vc setDelegate:self];
}
return self;
}
-(void)viewDidLoad
{
[super viewDidLoad];
}
-(void)sayHi
{
NSLog(#"hi");
}
#end
The - (IBAction)button:(id)sender method is connect to a button, but when clicked I get no output. What am I doing wrong?

Answer 1

ViewController.h:
#import <UIKit/UIKit.h>
#protocol testDelegate
-(void)sayHi;
#end
#interface ViewController : UIViewController
#end
ViewController.m:
#import "ViewController.h"
#import "DelegateController.h"
#interface ViewController () <testDelegate>
#end
#implementation ViewController
- (IBAction)pushNewViewController:(id)sender
{
DelegateController *dc = [[DelegateController alloc] init];
dc.delegate = self;
[self.navigationController pushViewController:dc animated:YES];
}
- (void)sayHi
{
NSLog(#"It works!");
}
#end
DelegateController.h:
#import "ViewController.h"
#interface DelegateController : UIViewController
#property (weak, nonatomic) id<testDelegate> delegate;
#end
DelegateController.m:
#import "DelegateController.h"
#implementation DelegateController
- (IBAction)button:(id)sender
{
if([_delegate respondsToSelector:#selector(sayHi)]) {
[_delegate performSelector:#selector(sayHi)];
}
}
#end

Answer 2

Try this:
ViewController.h
#import <UIKit/UIKit.h>
#class ViewController;
#protocol testDelegate
-(void)sayHi;
#end
#interface ViewController : UIViewController
- (IBAction)button:(id)sender;
#property (weak, nonatomic)id <testDelegate> delegate;
#end
ViewController.m
#import "ViewController.h"
#import "DelegateController.h"
#interface ViewController ()
#property (nonatomic, strong) DelegateController *dc;
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
_dc = [[DelegateController alloc] init];
[self setDelegate:_dc];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (IBAction)button:(id)sender
{
[self.delegate sayHi];
}
#end
DelegateController.h
#interface DelegateController : UIViewController <testDelegate>
#end
DelegateController.m
#import "DelegateController.h"
#interface DelegateController ()
#end
#implementation DelegateController
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self)
{
NSLog(#"init");
}
return self;
}
-(void)viewDidLoad
{
[super viewDidLoad];
}
-(void)sayHi
{
NSLog(#"hi");
}
#end

Answer 3

Your problem is that ViewController creates DelegateController, then in DelegateController you're creating a new, different, instance of ViewController, and setting yourself as the delegate of that instance. Normally, the way you set a delegate is that DelegateController would create an instance of ViewController and set itself as the delegate. This assumes that DelegateController is created first, but exactly how to do this depends on your app structure, and how you move from controller to controller.

Answer 4

Replace you button Click method with following
- (IBAction)button:(id)sender {
// Check whether your Delegate method is implemeted or not
if([delegate respondsToSelector:#selector(sayHi)])
{
// Call Delegate Method
[delegate performSelector:#selector(sayHi)];
}
}