LifeCycleMethods.swift

 override func viewDidLoad() {
        super.viewDidLoad()
        dragDropAreaView.delegate = self
        
        setupView()
    }
    
    override func viewDidAppear() {
        let flowLayout = NSCollectionViewFlowLayout()
        flowLayout.itemSize = NSSize(width: 160.0, height: 120.0)
        flowLayout.sectionInset = EdgeInsets(top: 10.0, left: 20.0, bottom: 10.0, right: 20.0)
        flowLayout.minimumInteritemSpacing = 20.0
        flowLayout.minimumLineSpacing = 20.0
        collectionView.collectionViewLayout = flowLayout
        
        view.wantsLayer = true
        collectionView.layer?.backgroundColor = #colorLiteral(red: 0.9215686275, green: 0.9215686275, blue: 0.9215686275, alpha: 1)
        collectionView.frame = dragDropAreaView.frame
    }