UICollectionView Not Appearing - objective-c

Question

I am trying to set up UICollectionView programatically in my view controller which extends UIViewController. For some reason, my collection view is not showing up at all. Below is what I have.
Why is it not appearing? I am hooking it up to the delegate and data source and adding it as a subview to self.view. What's missing in my code?
In my .h file:
#interface MainViewController : UIViewController
{
#private
UICollectionView *_collectionView;
NSMutableArray *_results; // data source array
}
#end
In my .m file:
#interface MainViewController () <UICollectionViewDataSource, UICollectionViewDelegateFlowLayout>
#property (nonatomic, retain) UICollectionView *collectionView;
#property (nonatomic, retain) NSMutableArray *results;
#end
#implementation MainViewController
#synthesize collectionView = _collectionView;
#synthesize results = _results;
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// some init stuff - nothing to do with collection view.
}
return self;
}
- (void)loadView
{
self.results = [NSMutableArray array];
UIImage *image1 = [UIImage imageNamed:#"img1.jpg"];
UIImage *image2 = [UIImage imageNamed:#"img2.jpg"];
[self.results addObject:image1];
[self.results addObject:image2];
self.collectionView.dataSource = self;
self.collectionView.delegate = self;
UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) collectionViewLayout:flowLayout];
self.collectionView = collectionView;
[self.view addSubview:self.collectionView];
[self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:#"Cell"];
[self.collectionView reloadData];
}
- (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section
{
return [self.results count];
}
- (NSInteger)numberOfSectionsInCollectionView: (UICollectionView *)collectionView
{
return 1;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"Cell" forIndexPath:indexPath];
cell.backgroundColor = [UIColor colorWithPatternImage:[self.results objectAtIndex:indexPath.row]];
return cell;
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
UIImage *image = [self.results objectAtIndex:indexPath.row];
return CGSizeMake(image.size.width, image.size.height);
}
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
return UIEdgeInsetsMake(50, 20, 50, 20);
}

Answer 1

I got errors trying to run your code unless I changed the loadView method to viewDidLoad -- according to the docs you're not supposed to directly call loadView. To get the data source and delegate methods to run, I moved the lines setting the delegate and data source to self below where you set self.collectionView = collectionView
self.collectionView = collectionView;
self.collectionView.dataSource = self;
self.collectionView.delegate = self;

Answer 2

Your numberOfSectionsInCollectionView: returns 0. For a collection view with one section, you should either return 1 or just not implement this method.
Also I cannot see where you alloc/init self.collectionView.

Answer 3

I ended up subclassing UICollectionViewController instead of UIViewController and changing the init method to:
- (id)initWithCollectionViewLayout:(UICollectionViewLayout *)layout
and it worked.

Answer 4

You only had to bind your CollectionView delegate, and dataSource to ViewController in the StoryBoard.enter image description here