Using delegate to push data back

Question

I use this code, but "it works" doesn't happen.

DetailViewController.h

[#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>

@protocol ProtocolNameDelegate

-(void)DoSomething;

@end

@interface DetailViewController : UIViewController {
     id<ProtocolNameDelegate> _delegate;
}

@property (strong, nonatomic) id<ProtocolNameDelegate> _delegate;

DetailViewController.m

@synthesize _delegate;

- (void)viewDidLoad
{
    [super viewDidLoad];

    [_delegate DoSomething];
}

MasterViewController.h

@interface MasterViewController : UITableViewController <ProtocolNameDelegate>

MasterViewController.m

-(void)DoSomething
{
    NSLog(@"It works");

}

I think i have to add something like:

MasterViewController* mvc = [[MasterViewController alloc] init];
    mvc._delegate = self;

But it gives an error, and by the way will it create another instance of MasterViewController?

You are creating delegate in detailViewController how could you access it from an object of masterViewController — Satheesh, Jul 23 '13 at 11:11
there is good explanation on SO, check this out http://stackoverflow.com/questions/5210535/passing-data-between-view-controllers — limon, Jul 23 '13 at 11:23

score 1 · Answer 1 · answered Jul 23 '13 at 11:12

1

Instead of

MasterViewController* mvc = [[MasterViewController alloc] init];
mvc._delegate = self;

write this,

DetailViewController* svc = [[DetailViewController alloc] init];
dvc._delegate = self;

You made mistake in implementation.

Abstract of implementation should be.

Create Protocol in DetailVC.
Create Property for Delegate, Synthesize, and make call.
Import DetailVC in MasterVC and include delegate in MasterVC.h
Implement protocol method in MasterVC.m
Create instance of DetailVC and assign DetailVCObj.delegate = self;

answered Jul 23 '13 at 11:12

βhargavḯ

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and i will have 2 instances of DetailViewController? – Horhe Garcia Jul 23 '13 at 11:39
No you need only one at the place from where you are presenting/pushing detailview. – βhargavḯ Jul 23 '13 at 11:40
i think it's because in this case i actually have 2 of them – Horhe Garcia Jul 23 '13 at 11:45
Try to do one thing. place button on detail and on button click call delegate method and test if it is working. – βhargavḯ Jul 23 '13 at 11:48
fixed that using SecondViewController *secondVC = (SecondViewController *) segue.destinationViewController; [secondVC setDelegate:self]; – Horhe Garcia Jul 23 '13 at 13:16

Puneet Sharma · Answer 2 · 2013-07-23T11:54:01.643

0

In MasterViewController.m, you need to allocate and intialise DetailViewController somewhere

DetailViewController* dvc = [[DetailViewControlleralloc] init];
    dvc._delegate = self;

Also, because you have written [_delegate doSomething] in

DetailviewController's viewDidLoad method,

it means you must set dvc._delegate = self; in MasterViewController.m

before loading dvc's view (before addSubview or anything that loads view).

edited Jul 23 '13 at 11:54

answered Jul 23 '13 at 11:12

Puneet Sharma

9,369
1
27
33

this made my code ok: SecondViewController *secondVC = (SecondViewController *) segue.destinationViewController; [secondVC setDelegate:self]; – Horhe Garcia Jul 23 '13 at 13:17

Using delegate to push data back

2 Answers2