Can not outsource UICollectionViewDatasource in extra class - ios

Question

I have a ViewController with a CollectionView and would like to put the UICollectionViewDataSource in an extra-class, so that it can be reused. (I'm not using the interface builder).
Therefore, I created an extra-class:
class MyDataSource: NSObject, UICollectionViewDelegate, UICollectionViewDataSource {
public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 5
}
public func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "MYIDENTIFIER", for: indexPath)
cell.backgroundColor = .blue
return cell
}
}
In the ViewController with the CollectionView, I set it:
override func viewDidLoad() {
super.viewDidLoad()
collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "MYIDENTIFIER")
let myDataSource = MyDataSource()
collectionView.delegate = myDataSource
collectionView.dataSource = myDataSource
}
However, the collectionView will stay empty - there are no cells on it.
However, if I put all the DataSource Functions into the ViewController class itself and set the delegate and DataSource to self, then everything works.
Is it not possible to outsource the UICollectionViewDataSource in other files, or is there anything more you have to do?

Answer 1

Just in case. Here is the reason I was saying about calling the init method. #Andrey Chernukha, sorry if it caused any confusion. This is why I said that it works with the init but I guess it is the same reason as Pascal
import UIKit
class ViewController: UIViewController {
lazy var collectionView : UICollectionView = {
let layout = UICollectionViewFlowLayout()
let cv = UICollectionView(frame: .zero, collectionViewLayout: layout)
cv.backgroundColor = .green
return cv
}()
var dataSource : CustomDataSource!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
self.view.addSubview(collectionView)
collectionView.frame = CGRect(x: 0, y: 0, width: self.view.frame.width, height: self.view.frame.height)
dataSource = CustomDataSource(collectionView: collectionView)
}
}
class CustomDataSource : NSObject, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout, UICollectionViewDelegate {
let collectionView : UICollectionView
init(collectionView: UICollectionView) {
self.collectionView = collectionView
super.init()
self.collectionView.dataSource = self
self.collectionView.delegate = self
self.collectionView.register(Cell.self, forCellWithReuseIdentifier: "cell")
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 3
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
cell.backgroundColor = .red
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: 100, height: 100)
}
}
class Cell : UICollectionViewCell {
override init(frame: CGRect) {
super.init(frame: frame)
setupViews()
}
func setupViews() {
self.backgroundColor = .red
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
I tested it and the reason is that dataSource is weak in a collectionView so it is deallocated immediately after it's instantiated if declared in viewDidLoad()

Answer 2

thanks for the help! I tried what Galo suggested, but for me this didn't work. However, I found the solution:
You have to initialize the delegate as property of the ViewController, and not in its viewDidLoad function! Then everything is working correctly!
let myDataSource = MyDataSource()
override func viewDidLoad() {
super.viewDidLoad()
collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "MYIDENTIFIER")
collectionView.delegate = myDataSource
collectionView.dataSource = myDataSource
}

Answer 3

It's another scope issue often been overlooked.
override func viewDidLoad() {
super.viewDidLoad()
collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "MYIDENTIFIER")
let myDataSource = MyDataSource(). //See the problem here?
collectionView.delegate = myDataSource
collectionView.dataSource = myDataSource
} //myDataSource will be released!