UICollectionView Always Shows Previous Selection Before Current

Question

I seem to be having a problem I have been trying to solve all day. I have a UICollectionView. Within this view, items from core data are shown(images). You click on the image and it goes to a detail view with more information that was inputted when the image was taken via the camera. The images show fine in the collection view. The problem I am having is that always before showing the current selection, the last selection is shown first. I don't know what to do, here is the code and some output.

{
NSInteger selectedFavoriteIndex;
}


- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
    // Custom initialization
}
return self;
}

- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.

}

- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (NSManagedObjectContext *)managedObjectContext
{
NSManagedObjectContext *context = nil;
id delegate = [[UIApplication sharedApplication]delegate];
if ([delegate performSelector:@selector(managedObjectContext)]) {
    context = [delegate managedObjectContext];
}
return context;

}

- (void)viewDidAppear:(BOOL)animated{
[super viewDidAppear:animated];


//Fetch all the stuff from data store.
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];

NSFetchRequest *fetchRequest =[[NSFetchRequest alloc]initWithEntityName:@"Favorites"];
self.favorites = [[managedObjectContext executeFetchRequest:fetchRequest error:nil]mutableCopy];
[self.collectionView reloadData];
[self.collectionViewLayout invalidateLayout];


}



-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 1;
}

-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:    (NSInteger)section
{
return [self.favorites count];
}

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"Cell";
CustomCollectionCell *customCell = [self.collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];

NSManagedObject *favorite = [self.favorites objectAtIndex:indexPath.row];
[customCell.collectionImageView setImage:[UIImage imageWithData:[favorite valueForKey:@"image"]]];
return customCell;



}
 - (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
selectedFavoriteIndex = indexPath.item;
NSLog(@"Index path: %@", indexPath);
NSLog(@"Selected Favorite Index: %ld", (long)selectedFavoriteIndex);
NSLog(@"IndexPath.row: %ld", (long)indexPath.row);
NSLog(@"IndexPath.item: %ld", (long)indexPath.item);


}  



-(void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath
{

}

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{

if ([[segue identifier]isEqualToString:@"moment"]) {
    NSManagedObject *selectedFavorite = [self.favorites objectAtIndex:selectedFavoriteIndex];
    ViewMomentViewController *viewMomentViewController = segue.destinationViewController;
    viewMomentViewController.favorite = selectedFavorite;
    viewMomentViewController.hidesBottomBarWhenPushed = YES;



}


}

The formatting kind of got messed up when pasting it here. The format is correct in Xcode though. Here is some output.

Index path: {length = 2, path = 0 - 1}

I am also confused as why the path is always subtracting, whether it be 0-0 or 0-2. Can someone explain that to me?

Answer 1

Sounds like prepareForSegue gets called before didSelectItemAtIndexPath. So prepareForSegue sees the value of selectedFavoriteIndex from the previous call to didSelectItemAtIndexPath.

This is really easy to confirm by placing NSLog statements in both methods to see the order in which the log message appear in the console.

There are a couple of ways to solve this:

1. Rather than using a storyboard-defined segue, do a programatic segue in didDeselectItemAtIndexPath after setting selectedFavoriteIndex using [self.storyboard instantiateViewControllerWithIdentifier:].

2. Instead of relying on didSelectItemAtIndexPath to set the selected index, determine the selected index in prepareForSegue by calling [self.collectionView indexPathForCell:sender] (when you use a storyboard segue from a collection view cell, the value of sender in prepareForSegue will be the cell itself, which you can use to determine the index path).

Approach (2) would look something like this:

NSIndexPath *indexPath = [self.collectionView indexPathForCell:sender];
NSManagedObject *selectedFavorite = [self.favorites objectAtIndex:indexPath.item];