How to maintain state of collection view cell after dismissal of view? - ios

Question

So I have a collectionView that holds an array of trends users can click to feature that photo. When the cell is clicked, a checkmark appears letting the user know they have selected that category and their photoId is then entered into the selected childValues in the database.
Users have the option to edit their photo if they decided they want to remove their photo from a certain category. When I select edit profile, the cells that should be selected (ones I choose while uploading the photo) are unselected.
Or lets say for example, I already have a photo uploaded but now I want to feature it, when I go to edit photo and tap on a category the checkmark appears telling me this category is chosen. When I press save the photo is added to the chosen childValue in the database as expected, but when I click edit profile again and the view is presented. The cells I choose 10 seconds ago are now unselected.
How can I maintain a selected or deselected state even after dismissing the view controller?
var selectedCategoryValues = [String]()
var trend: Trend!
var selectedIndex = -1
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
if collectionView == trendCollectionView {
let trendsCell = collectionView.dequeueReusableCell(withReuseIdentifier:
"trendsCell", for: indexPath) as! TrendsCollectionCell
trendsCell.layer.cornerRadius = 9.0
trendsCell.layer.borderWidth = 0.1
trendsCell.layer.borderColor = UIColor.lightGray.cgColor
if selectedIndex == indexPath.row {
trendsCell.isSelected = true
} else {
trendsCell.isSelected = false
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
if collectionView == trendCollectionView {
guard selectedIndex != indexPath.row else{return}
let indexpath = IndexPath(row:selectedIndex, section: 0)
trendCollectionView.cellForItem(at: indexpath)?.isSelected = !trendCollectionView.cellForItem(at: indexpath)!.isSelected
switch selectedSegmentIndex {
case 0: self.trend = femaleTrends[indexPath.row]
print("You selected \(trend.childValue)")
self.selectedCategoryValues.append(trend.childValue)
case 1: self.trend = maleTrends[indexPath.row]
print("You selected \(trend.childValue)")
self.selectedCategoryValues.append(trend.childValue)
default: break
}
Collection View Cell
class TrendsCollectionCell: UICollectionViewCell {
override var isSelected: Bool{
didSet{
if isSelected {
setSelectedUI()
}
else{
setUnSelectedUI()
}
}
}
func setSelectedUI(){
trendCheckmark.isHidden = false
trendCheckmark.tintColor = .white
}
func setUnSelectedUI(){
// reset to deafault, hide checkmark
trendCheckmark.isHidden = true
}
}

Answer 1

You can store the selected index as part of some state and then store / use that state as you wish. You'd do this by having some property selectedIndex, or, if you have more properties, you could have some struct viewState that you update in didSelectItemAt. You then either have some state manager outside of your view controllers (recommended) or you pass the state between view controllers (if you have a simple app).

Answer 2

Three needed steps for maintaining selected state of cell . This applicable for table view and collection view
1. Maintain last selected index for as selected cell .
2. Update cellindex on every did select call .
3. For every cellforrowindex method check if this selected cell or not.
Further explanation is on my previous answer
https://stackoverflow.com/questions/59293617/multiple-cells-selected-on-scrolling-reuse-cells-problem/

Answer 3

I never recommend using cell selected variable to detect cell selection because that variable is not completely describe the state , because of the dequeuing and recycling mechanism that work for UICollectionView and UITableView So I recommend Every time to rely all the state to your models ,
so you have 2 options
add an isSelcted property to every cell ModelObject
add Single property to your view Controller that reserve the selected Index
import Foundation
class NumberCountDataSource: NSObject , UICollectionViewDataSource {
let selectionAction: ((Int)->())
let numbersCount: Int
var selectedIndex: Int?
init(cardsCount: Int,selectionAction: #escaping ((Int)->())) {
self.numbersCount = cardsCount
self.selectionAction = selectionAction
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return numbersCount
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: NumberCollectionViewCell.identiefier, for: indexPath) as! NumberCollectionViewCell
cell.configure(number: indexPath.row + 1, isSelected: indexPath.row == selectedIndex)
return cell
}
}
extension NumberCountDataSource: UICollectionViewDelegate , UICollectionViewDelegateFlowLayout {
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
selectedIndex = indexPath.row
self.selectionAction(indexPath.row)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return CGFloat.init(0.0)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
return CGFloat.init(0.0)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize.init(width: 60, height: 50)
}
}
class NumberCollectionViewCell: UICollectionViewCell {
#IBOutlet weak var numberLable: UILabel!
#IBOutlet weak var backGroundview: AnimatableView!
static let identiefier: String = "NumberCollectionViewCell"
static let nibName: String = "NumberCollectionViewCell"
override func awakeFromNib() {
super.awakeFromNib()
// Initialization code
}
override var isSelected: Bool {
didSet {
setupSelection(iseSelected: isSelected)
}
}
private func setupSelection(iseSelected: Bool) {
backGroundview.backgroundColor = isSelected ? UIColor("#4d8ec5") : UIColor("#ffffff")
backGroundview.borderColor = isSelected ? UIColor.clear : UIColor("#707070")
numberLable.textColor = isSelected ? UIColor("#ffffff") : UIColor("#444e53")
}
func configure(number: Int,isSelected: Bool) {
numberLable.text = "\(number)"
setupSelection(iseSelected: isSelected)
}
}