Selected cell is deselected when switch to other page - ios

Question

I make a custom calendar using UICollectionView. From the calendar when I selected some dates and move forward to next month, then back again to the previous month, the selected item is deselected. Maybe it happens for reusable cell. How can I solve this problem.
For better understand what I want:
From September I select 4,5 then move to August/July/November (In this month maybe select some other dates or not)
Then return to September. In September I want to showed 4,5 as selected
I tried this using didSelectItemAt indexPath, but when return back to the September the selected item is deselected
public func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
if let cell = collectionView.cellForItem(at: indexPath) as? CalendarDateRangePickerCell {
if cell.isSelected == true {
cell.backgroundColor = .blue
cell.label.textColor = .white
cell.isUserInteractionEnabled = true
}
selectedDate = cell.date!
}
}

Answer 1

First create an array of selected Cells. If you are using a model to set data to cell, you can create an array of selected models. or you can create an array of selected rows.
Let's say you are using a model.
var selectedDates: [DateModel] = []
Then
public func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
if let cell = collectionView.cellForItem(at: indexPath) as? CalendarDateRangePickerCell {
selectedDate = cell.date!
if !selectedDates.contains(dataSourceModel[indexPath.row]) {
selectedDates.append(dataSourceModel[indexPath.row])
}
}
}
then in your cellForItem
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
if selectedDates.contains(dataSourceModel[indexPath.row]) {
cell.isSelected = true
}
}
Also make sure you remove you model when unSelected
func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
if selectedDates.contains(dataSourceModel[indexPath.row]) {
selectedDates.remove(dataSourceModel[indexPath.row])
}
}
*may contain some syntax error, but you can follow this path to get where you want.

Answer 2

Cells in UITableView and UICollectionView are reused when you scroll, that is why you should store which days selected in another place. Then, in cellForItem you should set isSelected.

Answer 3

Have you tried setting clearsSelectionOnViewWillAppear to false in viewDidLoad()?
A Boolean value indicating if the controller clears the selection when the collection view appears.
The default value of this property is true. When true, the collection view controller clears the collection view’s current selection when it receives a viewWillAppear(_:) message. Setting this property to false preserves the selection.
Source: Apple Developer Documentation