Change layout of UICollectionViewCell - ios

Question

I am using a UICollectionViewController to display a collection of UICollectionViewCell that a user can swipe between, on ios 13, swift 5, and UIKit. I ultimatelly want to re-draw the cell if the user has changed the orientation. In my controller, I have noticed that this piece of code gets executed on orientation change:
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cellId", for: indexPath) as! MyCell
return cell
}
In MyCell, I am using this code to monitor then a layout is re-initialized:
override init(frame: CGRect) {
super.init(frame: frame)
setLayout()
print("### orientation:: \(UIDevice.current.orientation.isLandscape) ")
}
Result: This method is called 2 times. When the app starts, and when I change from portrait to landscape. Any subsequent changes, do not call it. I suspect that this is fine, as maybe both versions are cached ( a landscape and a portrait ). If I add code to the setLayout() method based on the UIDevice.current.orientation.isLandscape flag, nothing changes while it executes. Note: The actual result of UIDevice.current.orientation.isLandscape is correct.
Here is an example of what is in my setLayout() method:
let topImageViewContainer = UIView();
topImageViewContainer.translatesAutoresizingMaskIntoConstraints = false
topImageViewContainer.backgroundColor = .yellow
addSubview(topImageViewContainer)
NSLayoutConstraint.activate([
topImageViewContainer.topAnchor.constraint(equalTo: topAnchor),
topImageViewContainer.leftAnchor.constraint(equalTo: leftAnchor),
topImageViewContainer.rightAnchor.constraint(equalTo: rightAnchor),
topImageViewContainer.heightAnchor.constraint(equalTo: heightAnchor, multiplier: 0.5)
])
if (UIDevice.current.orientation.isLandscape) {
let imageView = UIImageView(image: UIImage(named: "photo_a"))
imageView.translatesAutoresizingMaskIntoConstraints = false
imageView.contentMode = .scaleAspectFit
topImageViewContainer.addSubview(imageView)
} else {
let imageView = UIImageView(image: UIImage(named: "photo_b"))
imageView.translatesAutoresizingMaskIntoConstraints = false
imageView.contentMode = .scaleAspectFit
topImageViewContainer.addSubview(imageView)
}
In the example above, the code with "photo_a" is executing, but the ui is still showing photo_b. I suspect I am doing something wrong, and I need to somehow migrate towards an "Adaptive layout" as mentioned here: Different layouts in portrait and landscape mode . However, I am not sure how I could hook in some "viewWillTransition*" functions into a UICollectionViewCell that has a UIView.
How can I adjust my MyCell class, that implements UICollectionViewCell, to allow the cell to be updated when the user changes from landscape to protrait in a Swift intended way?

Answer 1

Hi try to check if is landscape or portrait in cellForItem, my example:
set colloectionView, flowLayaout and cell id:
class ViewController: UIViewController {
private var collectionView: UICollectionView?
let layout = UICollectionViewFlowLayout()
let cellId = "cellId"
now in viewDidLoad set collection view and layout parameters and the collection constraints:
layout.scrollDirection = .horizontal
collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
collectionView?.delegate = self
collectionView?.dataSource = self
collectionView?.backgroundColor = .clear
collectionView?.register(BottomCellTableViewCell.self, forCellWithReuseIdentifier: cellId)
collectionView?.contentInset = UIEdgeInsets(top: 0, left: 10, bottom: 0, right: 10)
collectionView?.showsHorizontalScrollIndicator = false
collectionView?.translatesAutoresizingMaskIntoConstraints = false
guard let collection = collectionView else { return }
view.addSubview(collection)
layout.itemSize = CGSize(width: view.bounds.size.width / 2, height: 200)
collection.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -20).isActive = true
collection.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor, constant: 0).isActive = true
collection.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: 0).isActive = true
collection.heightAnchor.constraint(equalToConstant: 200).isActive = true
after that conform to delegate and datasource in a separate extension (more clean code) and set in it numberOfItems and cellForRow:
extension ViewController: UICollectionViewDelegate, UICollectionViewDataSource {
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 10
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! BottomCellTableViewCell
// check here device orientation
if UIDevice.current.orientation.isLandscape {
let image = UIImage(named: "meB")
cell.imageV.image = image
} else {
let image = UIImage(named: "me")
cell.imageV.image = image
}
// reload the view and the collection
DispatchQueue.main.async {
self.collectionView?.reloadData()
}
return cell
}
}
In collectionViewCell adding a subview directly to the cell, and pinning the image view to the cell, is wrong. You add it to a contentView and pin to it relative constraints:
class BottomCellTableViewCell: UICollectionViewCell {
let imageV: UIImageView = {
let iv = UIImageView()
iv.image = UIImage(named: "me")
iv.contentMode = .scaleAspectFill
iv.clipsToBounds = true
iv.translatesAutoresizingMaskIntoConstraints = false
return iv
}()
override init(frame: CGRect) {
super.init(frame: frame)
contentView.backgroundColor = .red
contentView.addSubview(imageV)
imageV.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
imageV.leadingAnchor.constraint(equalTo: contentView.leadingAnchor).isActive = true
imageV.trailingAnchor.constraint(equalTo: contentView.trailingAnchor).isActive = true
imageV.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
This is the result: