UICollectionViewCell not updating view after selection - ios

Question

Have an issue where:
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath)
is called when an item is selected, but I cannot change any cell properties from this method.
I created a new project with a stripped down UICollectionViewController to change the background color of a cell when selected. It also doesn't work. Here it is:
import UIKit
private let reuseIdentifier = "Cell"
class CollectionViewController: UICollectionViewController {
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 5
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath)
cell.backgroundColor = UIColor.blue
return cell
}
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let cell = self.collectionView(self.collectionView, cellForItemAt: indexPath)
cell.backgroundColor = UIColor.green
}
}
The only thing I did in Storyboard is delete the standard View Controller and replace it with a UICollectionViewController, create a subclass of UICollectionViewController and set the controller in the storyboard as that class.
Also, I can confirm that the cell's index path is returned from this method when called from inside the didSelectItemAt method:
self.collectionView.indexPathsForSelectedItems

Answer 1

You are using the wrong API. Never call the delegate method collectionView(_ cellForItemAt:, use cellForItem(at:
if let cell = collectionView.cellForItem(at: indexPath) {
cell.backgroundColor = UIColor.green
}
But be aware that this change is not persistent. When the user scrolls the color will change back to blue.

Answer 2

You can achieve that as below,
ViewController
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ColoursViewCell", for: indexPath) as! ColoursViewCell
return cell
}
UICollectionViewCell
class ColoursViewCell: UICollectionViewCell {
#IBOutlet var photoImageView: UIImageView?
override var bounds: CGRect {
didSet {
self.layoutIfNeeded()
}
}
override var isSelected: Bool{
didSet{
if self.isSelected{
self.photoImageView?.backgroundColor = UIColor.random
}else{
self.photoImageView?.backgroundColor = UIColor.lightGray
}
}
}
}
you can have sample projects from this link I have in GitHub
https://github.com/hadanischal/RandomColors/tree/develop