iOS UICollectionView init and update custom cell - ios

Question

I'm trying to implement a custom cell with support for user tapping. Previously the functions related are:
func collectionView(collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueResuableCell(withReuseIdentifier: "CustomCell", for: indexPath) as! CustomCell
cell.setEmpty() // to init the cell
return cell
}
func collectionView(collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let cell = collectionView.cellForItem(at: indexPath) as ! CustomCell
//implementations
self.collectionView.reloadItem(at: [indexPath])
}
Then I noticed that after the tapping, the second function gets called first, but the first one also gets called afterwards, which means after tapping my cell will still be set to empty, so I changed the first function to this:
let cell = collectionView.dequeueResuableCell(withReuseIdentifier: "CustomCell", for: indexPath) as! CustomCell
if cell.valueInside == nil {
cell.setEmpty() // this will set valueInside to be a non-nil value
}
return cell
But it's still not working properly. I tracked the process: when loading the UI for the first time, init cell first (with the setEmpty() method); then after the tapping, cell is updated, and then the first function is called, but the cell obtained by this
collectionView.dequeueResuableCell(withReuseIdentifier: "CustomCell", for: indexPath) as! CustomCell
shows that the value inside is still nil, so the cell is not really up-to-date. How should I fix this? Or is my implementation logical (should I init the cell somewhere else instead of using this
check if it's nil -> then init
logic)?

Answer 1

func collectionView(collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
is called every time your inquire for a cell like
collectionView.cellForItem(at: indexPath)
or
self.collectionView.reloadItem(at: [indexPath])
The best way to use is to declare a class level variable like an array to hold the backed data, then for cell creating get data from that array and in your didSelectItemAt update that array and then just force the collection view to update that cell only.
// In your class scope
private var arData: [String] = ["One", "Two", "Three"] // This could be populated in viewDidLoad as well
// .... rest of your code
func collectionView(collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueResuableCell(withReuseIdentifier: "CustomCell", for: indexPath) as! CustomCell
//...
if indexPath.row < arData.count {
cell.valueInside = arData[indexPath.row]
} else {
cell.valueInside = "Default Value"
}
return cell
}
// ....
func collectionView(collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
//implementations
if indexPath.row < arData.count {
arData[indexPath.row] = "newValue"
self.collectionView.reloadItem(at: [indexPath])
}
}
This is the logic on how to correctly change a cell view content now if you want to change it's appearance again you should set the flag or whatever status distinguishing mechanism you have in the didSelectItemAt and just reload the cell considering cellForItemAt will refer to that status and apply's that appearance change.