Delegate method not firing?

Question

Just when I thought I had my head around how delegates work, it seems I am missing something.

I've setup a delegate like so:

ViewControllerA.h

@protocol LoginDelegate <NSObject>

-(void)userLoginSuccessful;

@end
@interface BBLoginViewController : BBBaseViewController
@property (weak, nonatomic) id <LoginDelegate> delegate; 

@end

ViewControllerA.m

-(void)someMethod 
{
    if ([self.delegate respondsToSelector:@selector(userLoginSuccessful)]){
                [self.delegate userLoginSuccessful];
            }
        [self dismissViewControllerAnimated:YES completion:nil];

}

ViewControllerB.m

    #import "ViewControllerA.h"

    @interface ViewControllerB () <UITableViewDataSource, UITableViewDelegate, LoginDelegate>


    -(void)viewWillAppear:(BOOL)animated
    {

        ViewControllerA *loginViewController = [[ViewControllerA alloc]init];
        loginViewController.delegate = self;

    }

#pragma mark - Login Delegate

-(void) userLoginSuccessful
{
  NSLog (@"Delegate fired!");
}

After all this my delegate method does not fire. What am I doing wrong? I looked at this SO answer and when checking the delegate is not nil - it is not. Its set to ViewControllerB.

Check your delegate method. you have defined this protocol method `userLoginSuccessful` and you are calling `-(void)expanItemImage:(UITapGestureRecognizer *)tap` — ChintaN -Maddy- Ramani, May 20 '14 at 07:42
And you do not need to check if your delegate responds to the protocol selector since you defined it correctly as a type conforming to the LoginDelegate protocol. — giorashc, May 20 '14 at 07:42
Copy and paste error - updated the question. Sorry gents. I removed the IF statement checking if the selector responds to the delegate and it still doesn't get called — Robert J. Clegg, May 20 '14 at 07:44
Do you reach the line [self.delegate userLoginSuccessful]; ? — streem, May 20 '14 at 07:45
I reach the if statement. Which never executes. Removing the statement and just calling [self.delegate userLoginSuccessful]; doesn't work either. — Robert J. Clegg, May 20 '14 at 07:46
@giorashc why? Its always better to check your delegate respond to the corresponding selector. You can avoid a crash some times. — Anil Varghese, May 20 '14 at 07:48
It's probably not the same instance of ViewControllerA. How do you add ViewControllerA to ViewControllerB ? — streem, May 20 '14 at 07:49
@Anil true for optional methods declared in a protocol but in his case he has only one required method. — giorashc, May 20 '14 at 07:50
Its better if you follow some conventions, will help you future :) — Anil Varghese, May 20 '14 at 07:52
I've always used the if statement to check the selector as I have had crashes before due to that very reason. Now I just implement it and know 100% I will never get a crash because it was sent to a class that has no idea what its about. — Robert J. Clegg, May 21 '14 at 08:53
@Tander this can go either way since now you will not know you have a problem espcially if the selector does not preform something that is visible — giorashc, May 21 '14 at 11:17

score 3 · Answer 1 · answered May 20 '14 at 07:49

3

This code:

-(void)viewWillAppear:(BOOL)animated
{

    ViewControllerA *loginViewController = [[ViewControllerA alloc]init];
    loginViewController.delegate = self;

}

Will create a ViewControllerA object and then (almost) immediately destroy it and is not what you intended.

You probably want to be setting the delegate in the prepareForSegue: method anyway...

answered May 20 '14 at 07:49

trojanfoe

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+1 - **(almost) immediately destroy it and is not what you intended.** – Kumar KL May 20 '14 at 07:54
ViewControllerB is present modally over viewControllerA. I am not using pprepareForSegue method. – Robert J. Clegg May 20 '14 at 07:54
@Tander Well your code is not how you create and use view controllers is it. – trojanfoe May 20 '14 at 07:55
@Tander try to set the delegate before presenting `ViewControllerB` – Anil Varghese May 20 '14 at 07:56
@Anil when would be the best time to set the delegate? – Robert J. Clegg May 20 '14 at 07:57
That depends. I would prefer setting delegate before moving to the next view. If you are presenting modally just before `presentViewController` of if you are using segue in `prepareForSegue` – Anil Varghese May 20 '14 at 08:00
Anyway currently what you are doing is wrong. if you can show me the presentation code i will point out – Anil Varghese May 20 '14 at 08:02
@Anil You're correct. I was setting the delegate incorrectly while presenting the view controller. I needed to set it just before presentViewController method - it works perfectly now. Make your comment an answer and I will accept it. Thank you! – Robert J. Clegg May 20 '14 at 08:06

score 2 · Accepted Answer · answered May 20 '14 at 08:12

2

Set the delgate before presenting ViewControllerB. The below code is not required anymore

-(void)viewWillAppear:(BOOL)animated
  {
     ViewControllerA *loginViewController = [[ViewControllerA alloc]init];
     loginViewController.delegate = self;

  }

Dont do like that. It will give you unexpected results. Remember always set the delegate before moving to the next view. If you are presenting modally just before presentViewController of if you are using segue in prepareForSegue

answered May 20 '14 at 08:12

Anil Varghese

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"It will give you unexpected results". Errr, I think the results can be predicted exactly. – trojanfoe May 20 '14 at 08:20
1

@trojanfoe lol:) yeah exactly.. not the result what you intended! – Anil Varghese May 20 '14 at 08:35

Delegate method not firing?

2 Answers2