- Init flowLayout and setup some params.
let waterFlowLayout = RLWaterfallFlowLayout()
waterFlowLayout.columnCount = 3
waterFlowLayout.sectionInset = UIEdgeInsets(top: 20, left: 10, bottom: 20, right: 10)
waterFlowLayout.columSpacing = 10
waterFlowLayout.rowSpacing = 10
waterFlowLayout.delegate = self
2.Make ViewController extends RLWaterfallFlowLayoutDelegate and implement delegate methods
func itemHeight(_ collectionView: UICollectionView?, indexPath: IndexPath) -> CGFloat {
return itemHeight[indexPath.item]
}