Swift 3 Warning in UICollectionViewDelegate

I am using Xcode 8 and Swift 3. I was designing the UICollectionView and wanted to set height and width dynamically so wanted for some answers. On the way I got this solution(Correct or not - I have No Idea):

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {

    let Labell : UILabel = UILabel()
    Labell.text =   self.items[indexPath.item]
    let labelTextWidth =   Labell.intrinsicContentSize.width
    return CGSize(width: labelTextWidth + 20, height: 35)

}

But this answer was in swift 2.0 And person who gave this answer claims that it is solved one. I pasted it in Xcode and changed some thing that Xcode suggested me.

Now here I am getting following warning:

instance method 'collectionView:layout:sizeForItemAtIndexPath:)' nearly matches optional requirement 'collection(_:willDisplaySupplementaryView:forElement:at:)' of protocol 'UICollectionViewDelegate'

Xcode suggests me 2 solutions 1) add private ahead of func keyword 2) add @nonobjc in front of fun keyword

I tried both solutions and it suppresses the warning but none the above is never called. I tried putting break point and tried many ways. If anyone can pull me out of this pit.

There is no sizeForItemAtIndexPath delegate method for UICollectionViewDelegate.

What you're probably looking for is

optional func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize

which can be found on the UICollectionViewDelegateFlowLayout protocol.

Try replacing your code with this:

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

    let Labell : UILabel = UILabel()
    Labell.text =   self.items[indexPath.item]
    let labelTextWidth =   Labell.intrinsicContentSize.width
    return CGSize(width: labelTextWidth + 20, height: 35)

}