Let only select specific cells with shouldSelectItemAt indexPath function - swift

Question

I want that only four specific cells can be selected at one time. When a button is pressed, I want that the selectable cells are 4 indexPath.row lower.
Example: In the beginning, indexPath.row 44-47 is selectable. If the button is pressed I want, that the indexPath.row 40-43 is selectable and so on.
I thought about making an array with the indexPath and If the button is pressed, the numbers in the array are 4 numbers lower.
Than I don't know, how to add this to the shouldSelectItemAt indexPath function.
How can I realize this?

Answer 1

You can use an IndexSet.
var allowedSelectionRow: IndexSet
allowedSelectionRow.insert(integersIn: 44...47) //Initial allowed selection rows
In collectionView(_:shouldSelectItemAt:)
return allowedSelectionRow.contains(indexPath.row) //or indexPath.item
Whenever you need:
allowedSelectionRow.remove(integersIn: 44...47) //Remove indices from 44 to 47
allowedSelectionRow.insert(integersIn: 40...43) //Add indices from 40 to 43
Advantage from an Array: Like a set, there is unicity of the values (no duplicates). Contains only integers, and you can add in "range" which can be useful (not add all the indices, but a range).
After comments, if you have only 4 rows allowed and consecutive, you can have that method:
func updateAllowedSectionSet(lowerBound: Int) {
let newRange = lowerBound...(lowerBound+3)
allowedSectionRow.removeAll() //Call remove(integersIn:) in case for instance that you want always the 1 row to be selectable for instance
allowedSectionRow.insert(integersIn: newRange)
}
For the first one, you just need to do:
updateAllowedSectionSet(lowerBound: 44) instead of allowedSelectionRow.insert(integersIn: 44...47)

Answer 2

Let's consider that the items form a String array, and you are keeping track of the selected indices as a Range.
var selectedRange: Range<Int>? {
didSet {
collectionView.reloadData()
}
}
var items: [String] = [] {
didSet {
// To make sure that the selected indices are reset everytime this array is modified,
// so as to make sure that nothing else breaks
if items.count >= 4 {
// Select the last 4 items by default
selectedRange = (items.count - 4)..<items.count
} else if !items.isEmpty {
selectedRange = 0..<items.count
} else {
selectedRange = nil
}
}
}
Then, when you are pressing the button to decrement the range, you can use this logic to handle the same:
func decrementRange() {
if var startIndex = selectedRange?.startIndex,
var endIndex = selectedRange?.endIndex {
startIndex = max((startIndex - 4), 0)
endIndex = min(max((startIndex + 4), (endIndex - 4)), items.count)
selectedRange = startIndex..<endIndex
}
}
Then, you can identify whether the the selection is being done on the active range using:
func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool {
if let selectedRange = selectedRange {
return selectedRange.contains(indexPath.item)
}
return false
}
Note: I would advice you to verify whether this covers all the corner cases before trying it out for production code.