UICollectionView: must be initialized with a non-nil layout parameter

i got the same problem and mine got solved by using

UICollectionViewFlowLayout *myLayout = [[UICollectionViewFlowLayout alloc]init];
[myLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
[myLayout setMinimumInteritemSpacing:0.0f];
[myLayout setMinimumLineSpacing:0.0f];
UICollectionView *myCollectionView = [[UICollectionView alloc]initWithFrame:viewfame collectionViewLayout:myLayout];

instead of

UICollectionView *myCollectionView = [[UICollectionView alloc]initWithFrame:self.view.frame];
[myLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
[myLayout setMinimumInteritemSpacing:0.0f];
[myLayout setMinimumLineSpacing:0.0f];
[myCollectionView setCollectionViewLayout:myLayout];

This worked for me :

UICollectionViewFlowLayout *aFlowLayout = [[UICollectionViewFlowLayout alloc] init];
    [aFlowLayout setItemSize:CGSizeMake(200, 140)];
    [aFlowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
myCollectionViewController = [[MyCollectionViewController alloc]initWithCollectionViewLayout:flowLayout];

If you are creating UICollectionView programmatically a layout is required.

As it turns out the problem was with registerClass:. I had this:

[self.collectionView registerClass:[UICollectionView class] 
        forCellWithReuseIdentifier:@"MyCell"];

but it should have been this:

[self.collectionView registerClass:[UICollectionViewCell class] 
        forCellWithReuseIdentifier:@"MyCell"];

So the dequeue method was creating a UICollectionView instead of a UICollectionViewCell.

If you are making collection view controller programmatically in UICollectionViewController make sure that UICollectionViewController init method uses [super initWithCollectionViewLayout] instead of [super init], e.g.:

-(id) initWithImages:(NSArray *)pImages {
    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
    [layout setMinimumInteritemSpacing:0.0f];
    [layout setMinimumLineSpacing:0.0f];
    layout.scrollDirection = UICollectionViewScrollDirectionVertical;
    if (self = [super initWithCollectionViewLayout:layout]) {
        _images= [[NSArray alloc] initWithArray:pImages];
    }
    return self;
}

From: UICollectionViewController Class Reference:Overview