Question

I’m doing something that involves a collection view with photos in it, and upon selecting one of the cells, it will segue into a new view where it shows a larger image.

Heres prepare for segue

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
    if ([segue.identifier isEqualToString:@"showPhotoSegue"]) {
        NSIndexPath *ip = [self.photoCollectionView indexPathForCell:sender];
        PhotoDisplayViewController *viewController = segue.destinationViewController;
        Photo* photo = [self.fetchedResultsController objectAtIndexPath:ip];
        NSLog(@"setting PHOTO at indexPath %@", ip);
        [viewController setPhoto:[UIImage imageWithContentsOfFile:photo.url]];
    }

}

And heres didSelectItemAtIndexPath

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{
    NSString *identifier = @"showPhotoSegue";
    [self performSegueWithIdentifier:identifier sender:self];
    NSLog(@"Selected item at %@", indexPath);
}

My view is always empty so i added the print line statements, and it seems the output is always something like

Selected cell at <NSIndexPath 0x1e084940> 2 indexes [0, 0], detail view controller 

So my question is, why is NSIndexPath always a pair of 2 indicies, and also how do i use it in my prepareforsegue to set the view for the segue

Thanks

Answer 1

In prepareForSegue:sender:, you expect sender to be a UICollectionViewCell.

In collectionView:didSelectItemAtIndexPath:, you are passing self (your UICollectionViewDelegate) as the sender argument. I suspect your collection view delegate is not a collection view cell.

Instead of sending the collection view delegate as sender, and expecting to receive a cell as sender, why not pass the index path as sender and expect to receive it as sender?

static NSString const *kShowPhotoSegueIdentifier = @"showPhotoSegue";

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    [self performSegueWithIdentifier:kShowPhotoSegueIdentifier sender:indexPath];
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([segue.identifier isEqualToString:kShowPhotoSegueIdentifier]) {
        [self prepareForShowPhotoSegue:segue withIndexPath:sender];
    }
}

- (void)prepareForShowPhotoSegue:(UIStoryboardSegue *)segue withIndexPath:(NSIndexPath *)indexPath {
    PhotoDisplayViewController *viewController = segue.destinationViewController;
    Photo* photo = [self.fetchedResultsController objectAtIndexPath:indexPath];
    [viewController setPhoto:[UIImage imageWithContentsOfFile:photo.url]];
}