CODEWITHSUNDEEP
iosobjective-cuiviewcontrollerdelegatesparameter-passing
Jon M
Jon M

Reputation: 664

Passing variables back to a ViewController using a Delegate does not work

I found a really good walk through of how to pass string values back from a ViewController to a calling ViewController and got it working perfectly. The example is really very good.

https://www.youtube.com/watch?v=YVikeoR3gYg

That said, the technique for passing back content seems relatively straight forward now that I have seen it, even if it's not that intuitive.

The example code however only includes two controllers. When I replicated the code using a much more detailed Storyboard, the code simply doesn't work. In my test app, I even embedded the calling Controller inside a NavigationController to see whether this would have an affect, but it still continued to work fine.

In my application, the ViewController is embedded within a NavigationController that is called via a SWRevealController segue class. I don't know if this is important or relevant but I am mentioning it.

I then call a CollectionViewController to choose an icon that should be passed back to the calling ViewController.

When I select the icon, I correctly identify the icon and pop

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    selectedIcon = [placeIcons objectAtIndex:indexPath.row];
    NSLog(@"In IconCollectionViewControlled - selected %@", selectedIcon);

    NSString *itemToPassBack = @"12345";      // Just testing any old string here...

// [self.delegate passBackIcon:selectedIcon]; // commenting out while testing

    [self.delegate passBackIcon:itemToPassBack];
    [self.navigationController popViewControllerAnimated:YES];
}

I get a correct trace suggesting that the right icon is selected. I would then expect that the text '12345' would be passed back to the calling Controller.

In my calling Controller, I have the following:

- (void)passBackIcon:(NSString *)iconName {
    NSLog(@"Icon to use is %@", iconName);
}

But this just isn't being called at all (or at least I'm not seeing the NSLog being shown. It's just being ignored.

The delegate is being correctly declared as far as I can tell.

Am I missing something?

Upvotes: 1

Views: 177

Answers (3)

DookieMan
DookieMan

Reputation: 1044

I've found this to be the easiest way to pass string and other information around using a tableView.

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

ViewControllerYouWantToPassToo *result = [self.storyboard instantiateViewControllerWithIdentifier:@"NameOfTheViewController"];

result.stringName = @"12345" // String Name is a NSString property you set up in the ViewController you want to pass too 

[self.navigationController pushViewController:result animated:YES];

[tableView deselectRowAtIndexPath:indexPath animated:YES];

}

Upvotes: 1

Klinkert0728
Klinkert0728

Reputation: 326

assuming you are working with segues, in the method prepareSegue you should setting the delegate for Example :

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
 {
     if ([segue.identifier isEqualToString:@"YOUR_SEGUE_IDENTIFIER"] ) {
        DestinationVc *vc = (DestinationVc *)segue.destinationViewController;
        [vc setDelegate:self];
     }

}

Hope it works for you

Upvotes: 2

Tommy Devoy
Tommy Devoy

Reputation: 13549

I suggest you wrapping your delegate in a check to see that it is valid and that it has adopted the respective method (if optional). 

if(self.delegate && [self.delegate respondsToSelector:@selector(passBackIcon:)]){
    [self.delegate passBackIcon:itemToPassBack];
}else{
    NSLog(@"Your delegate is not setup correctly");
}

If it enters the else, you have not set the delegate properly..ie you likely never did 

self.delegate = SomeInstanceOfAClassThatAdoptsYourDelegate;

Upvotes: 0

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