Can't get UICollectionView to display cells

Question

I'm trying to get a UICollectionView to display inside a modally presented view controller. The app is for iPad iOS 7.

I've created subclass of UIViewController (with a nib) and added it like this:

MyViewController *controller = [[MyViewController alloc] init];
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:controller];
navController.modalPresentationStyle = UIModalPresentationFullScreen;
navController.navigationBar.barStyle = UIBarStyleBlackTranslucent;

[self presentViewController:navController animated:YES completion:nil];

This view controller is to be the delegate and dataSource for my UICollectionView so I've added UICollectionViewDataSource and UICollectionViewDelegate to the header.

I've put a UICollectionView into the nib and added an outlet to MyViewController:

@property (strong, nonatomic) IBOutlet MyCollectionView *collectionViewController;

I've added this in viewDidLoad in MyViewController:

self.collectionViewController.dataSource = self;
self.collectionViewController.delegate = self;

I've also added the following to MyViewController:

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    NSLog(@"Items in section: %d", itemsArray.count); // returns correct amount

    return itemsArray.count;
}


- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    NSLog(@"cellForItemAtIndexPath %@", indexPath); // returns as expected

    static NSString *identifier = @"MyCell";

    [self.collectionViewController registerClass:[MyCollectionCell class] forCellWithReuseIdentifier:identifier];

    MyCollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];

    UIImageView *myImageView = (UIImageView *)[cell viewWithTag:100];
    myImageView.image = [UIImage imageNamed:[itemsArray objectAtIndex:indexPath.row]];

    return cell;
}

I've also set up a subclass of UICollectionViewCell with the identifier set to MyCell and added to it a UIImageView with the tag 100.

Whenever I bring up this view controller I'm getting the navigation bar as expected, but the UICollection view I've added to my nib is nowhere to be seen. All I'm seeing is black where the collection view should be. If I change the background colour of MyCollectionView from default to white, I see white where the collection view ought to be. It seems to be bringing up MyCollectionView, but not showing any cells.

Answer 1

One other point of interest is that if you set the cell's identifier in the nib or storyboard, don't register the nib/class in the collection view controller. Do one or the other, but not both.

Answer 2

If you link your collectionView and its own dataSource and delegate in your xib file, you don't need to set up this on your code.

Next, you need to register your UICollectionViewCell :

- (void)viewDidLoad 
{
    [super viewDidLoad];

    // Register Nib
    [self.collectionView registerNib:[UINib nibWithNibName:CollectionViewCell_XIB bundle:[NSBundle mainBundle]] forCellWithReuseIdentifier:CollectionViewCell_ID];
}

CollectionViewCell_XIB is the name of your cell xib CollectionViewCell_ID is the ID of your cell

And you need to implement cellForItemAtIndexPath like this :

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CollectionViewCell *cell = (CollectionViewCell *)[self.collectionView dequeueReusableCellWithReuseIdentifier:CollectionViewCell_ID forIndexPath:indexPath];

    // Configure cell with data
     UIImageView *myImageView = (UIImageView *)[cell viewWithTag:100];
    myImageView.image = [UIImage imageNamed:[itemsArray objectAtIndex:indexPath.row]];

    // Return the cell
    return cell;
}