回忆一下 collectionView 上的 didSelectItemAt

Question

In my project, there is label inside the collectionView cell that when user taps on it, the color of the label will change I did that with these codes

public func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
      if let cell = collectionView.cellForItem(at: indexPath) as? CaseCell {
         cell.selectCell()
      }
   }
   
   public func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
      if let cell = collectionView.cellForItem(at: indexPath) as? CaseCell {
         cell.deSelectCell()
      }
   }

Now, I want when user open this page and he/she already tap on any of them before, the selectCell will be called again. I can say in the cellForRowAt if the cell is the selected cell, call that function, but it wont behave like didSelectItemAt and didSelectItemAt . So how can I set when the page gets opened, it call didSelectItemAt and tap on the specific index? Then I when I add on the another cell, didSelectItemAt is also called. Thank you so much

---

here is my sulation, I don't know it's acceptable or not

for example, I set the selected row to index.row == 2

public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
      let cell = collectionView.dequeueReusableCell(reusableType: CaseCell.self, indexPath: indexPath)
      cell.configure(text: cases[indexPath.row])
      if indexPath.row == 2 {
         cell.selectCell()
      } else {
         cell.deSelectCell()
      }
      return cell
   }
   
   public func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
      if let cell = collectionView.cellForItem(at: indexPath) as? CaseCell {
         
         for index in 0..<cases.count {
            let index = IndexPath(row: index, section: 0)
            let deselctCell = collectionView.cellForItem(at: index) as? CaseCell
            deselctCell?.deSelectCell()
         }
         
         cell.selectCell()
      }
   }

Answer 1

A better approach would be to use both didSelect and didDeselect method to handle the selection and deselection of cells instead of interating through the entire collection of cells.

public func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
    if let cell = collectionView.cellForItem(at: indexPath) as? CaseCell {
        cell.deSelectCell()
    }
}

public func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    if let cell = collectionView.cellForItem(at: indexPath) as? CaseCell {
        cell.selectCell()
    }
}

Answer 2

My suggestion is to create a property for the currently selected index path. You can set it to a default value

var selectedIndexPath : IndexPath? = IndexPath(row: 2, section: 0)

The most reliable way is to modify the cells only in cellForItemAt , nowhere else. Depending on selectedIndexPath select or deselect the sell.

public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
   let cell = collectionView.dequeueReusableCell(reusableType: CaseCell.self, indexPath: indexPath)
   cell.configure(text: cases[indexPath.row])
   indexPath == selectedIndexPath ? cell.selectCell() : cell.deSelectCell()
   return cell
}

In didSelectItemAt change the value of selectedIndexPath and reload both the current and the previous cell.

public func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
{
    if selectedIndexPath != indexPath  {
        let indexPathsToReload = selectedIndexPath == nil ? [indexPath] : [selectedIndexPath!, indexPath]
        selectedIndexPath = indexPath
        collectionView.reloadItems(at: indexPathsToReload)
    } else {
        selectedIndexPath = nil
        collectionView.reloadItems(at: [indexPath])
    }
}

didDeselectedItemAt is not needed.

The code considers also the case of an empty selection. If you don't want this declare selectedIndexPath as non-optional

var selectedIndexPath = IndexPath(row: 2, section: 0)

and change didSelectItemAt to

public func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
{
    guard selectedIndexPath != indexPath else { return }
    let indexPathsToReload = [selectedIndexPath, indexPath]
    selectedIndexPath = indexPath
    collectionView.reloadItems(at: indexPathsToReload)
}