How to create and use UIcollectionView programmatically?

There is not alternative to create or allocate cells in itemAtIndex method. We need to register the customised class to create any views inside the custom class. something like this :

[UICollectionView registerClass:[CustomCollectionViewClass class] forCellWithReuseIdentifier:@"cellIdentifier"];

here is the best link which I found useful. Hope it helps others