What is the difference of implementation between UITableView & UICollectionView when using Xib? - ios

Question

I try to implement TableView and CollectionView with Xib Files. I implement UITableview properly but when I try to implement ColletionView I get an error "libc++abi.dylib: terminating with uncaught exception of type NSException". I got this error in var collectionView = UICollectionView() line.
Why I dont get this error this line var tableView = UITableView() ? And where is my mistake ? And What is the solution ? Thanks in advance.
var tableView = UITableView()
var collectionView = UICollectionView()
override func viewDidLoad() {
super.viewDidLoad()
let headerMenu = UIView()
headerMenu.translatesAutoresizingMaskIntoConstraints = false
headerMenu.backgroundColor = .green
self.view.addSubview(headerMenu)
headerMenu.heightAnchor.constraint(equalToConstant: 48.0).isActive = true
headerMenu.widthAnchor.constraint(equalToConstant: UIScreen.main.bounds.width).isActive = true
headerMenu.topAnchor.constraint(equalTo: view.safeTopAnchor).isActive = true
collectionView.delegate = self
collectionView.dataSource = self
collectionView.translatesAutoresizingMaskIntoConstraints = false
headerMenu.addSubview(collectionView)
collectionView.topAnchor.constraint(equalTo: headerMenu.topAnchor, constant: 0).isActive = true
collectionView.bottomAnchor.constraint(equalTo: headerMenu.bottomAnchor, constant: -10).isActive = true
collectionView.rightAnchor.constraint(equalTo: headerMenu.rightAnchor, constant: -10).isActive = true
collectionView.leftAnchor.constraint(equalTo: headerMenu.leftAnchor, constant: 10).isActive = true
collectionView.register(UINib(nibName: "MenuCollectionViewCell", bundle: nil), forCellWithReuseIdentifier: "MenuCollectionViewCell")
let mainView = UIView()
mainView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(mainView)
mainView.topAnchor.constraint(equalTo: headerMenu.bottomAnchor, constant: 0).isActive = true
mainView.bottomAnchor.constraint(equalTo: view.safeBottomAnchor, constant: 0).isActive = true
mainView.rightAnchor.constraint(equalTo: view.safeRightAnchor, constant: 0).isActive = true
mainView.leftAnchor.constraint(equalTo: view.safeLeftAnchor, constant: 0).isActive = true
mainView.backgroundColor = UIColor.white
tableView.delegate = self
tableView.dataSource = self
tableView.translatesAutoresizingMaskIntoConstraints = false
tableView.estimatedRowHeight = UITableViewAutomaticDimension
mainView.addSubview(tableView)
tableView.topAnchor.constraint(equalTo: mainView.topAnchor, constant: 0).isActive = true
tableView.bottomAnchor.constraint(equalTo: mainView.bottomAnchor, constant: -10).isActive = true
tableView.rightAnchor.constraint(equalTo: mainView.rightAnchor, constant: -10).isActive = true
tableView.leftAnchor.constraint(equalTo: mainView.leftAnchor, constant: 10).isActive = true
tableView.separatorStyle = .none
tableView.register(UINib(nibName: "ProductTableViewCell", bundle: nil), forCellReuseIdentifier: "ProductTableViewCell")
}

Answer 1

You need to use other init to create UICollectionView instance:
let layout = UICollectionViewFlowLayout()
let collectionView = UICollectionView(frame: rect, collectionViewLayout: layout)

Answer 2

UICollectionView requires a UICollectionViewLayout in order to render. When creating a collection view via the storyboard this is already set with a default value.
You can initialise it like this:
let flowLayout = UICollectionViewFlowLayout()
let collectionView = UICollectionView(frame: self.view.bounds, collectionViewLayout: flowLayout)
Flow layout
A concrete layout object that organizes items into a grid with optional header and footer views for each section.
The flow layout is one of the default/built in options and is useful for creating a 'bookshelf' style grid in which the columns fill left to right and then top to bottom (unless you change the width).
There is a good tutorial on the Ray Wenderlich website which explains more about collection views and their layouts