How to converting following Swift code in Objective-C?

Question

I am trying to learn self-sizing UICollectionView Cell techniques using a certain tutorial. I can't figure out how to write this following swift code in objective-c:

if let cvl = collectionViewLayout as? UICollectionViewFlowLayout {
    cvl.estimatedItemSize = CGSize(width: 150, height: 75)
  }

Can someone please help?

Answer 1

In Swift, the if-let construction is equivalent to nil-checking in Obj-C. The as keyword is used for casting. The question mark makes it an optional type, which is a value that can hold nil or a value. Non-optional values cannot hold nil, and if you attempt to "unwrap" a nil optional you will get a runtime error.

In Obj-C (this should be equivalent):

UICollectionViewFlowLayout * cvl = (UICollectionViewFlowLayout)collectionViewLayout;
if (cvl){
    cvl.estimatedItemSize = CGSizeMake(150, 75);
}

CGGeometry documentation