Animate CollectionViewCell after deleting item - ios

Question

For my CollectionView I have this animation inside willDisplay :
func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
// Add animations here
let animation = AnimationFactory.makeMoveUpWithFade(rowHeight: cell.frame.height, duration: 0.5, delayFactor: 0.1)
let animator = Animator(animation: animation)
animator.animate(cell: cell, at: indexPath, in: collectionView)
}
This is how the animation works (I implemented it for CollectionView) if you need it for more info.
Probelm:
Inside my project the user can create and delete an item.
Right now the collectionView is not animating after deleting even though I am calling reloadData:
extension MainViewController: DismissWishlistDelegate {
func dismissWishlistVC(dataArray: [Wishlist], dropDownArray: [DropDownOption]) {
self.dataSourceArray = dataArray
self.dropOptions = dropDownArray
self.makeWishView.dropDownButton.dropView.tableView.reloadData()
// reload the collection view
theCollectionView.reloadData()
theCollectionView.performBatchUpdates(nil, completion: nil)
}
}
This is where I call the delegate inside my other ViewController:
func deleteTapped(){
let alertcontroller = UIAlertController(title: "Wishlist löschen", message: "Sicher, dass du diese Wishlist löschen möchtest?", preferredStyle: .alert)
let deleteAction = UIAlertAction(title: "Löschen", style: .default) { (alert) in
DataHandler.deleteWishlist(self.wishList.index)
self.dataSourceArray.remove(at: self.currentWishListIDX)
self.dropOptions.remove(at: self.currentWishListIDX)
// change heroID so wishlist image doesnt animate
self.wishlistImage.heroID = "delete"
self.dismiss(animated: true, completion: nil)
// update datasource array in MainVC
self.dismissWishlistDelegate?.dismissWishlistVC(dataArray: self.dataSourceArray, dropDownArray: self.dropOptions)
}
let cancelAction = UIAlertAction(title: "Abbrechen", style: .default) { (alert) in
print("abbrechen")
}
alertcontroller.addAction(cancelAction)
alertcontroller.addAction(deleteAction)
self.present(alertcontroller, animated: true)
}
When creating the animation works just fine. This is how my createDelegateFunction looks like this:
func createListTappedDelegate(listImage: UIImage, listImageIndex: Int, listName: String) {
// append created list to data source array
var textColor = UIColor.white
if Constants.Wishlist.darkTextColorIndexes.contains(listImageIndex) {
textColor = UIColor.darkGray
}
let newIndex = self.dataSourceArray.last!.index + 1
self.dataSourceArray.append(Wishlist(name: listName, image: listImage, wishData: [Wish](), color: Constants.Wishlist.customColors[listImageIndex], textColor: textColor, index: newIndex))
// append created list to drop down options
self.dropOptions.append(DropDownOption(name: listName, image: listImage))
// reload the collection view
theCollectionView.reloadData()
theCollectionView.performBatchUpdates(nil, completion: {
(result) in
// scroll to make newly added row visible (if needed)
let i = self.theCollectionView.numberOfItems(inSection: 0) - 1
let idx = IndexPath(item: i, section: 0)
self.theCollectionView.scrollToItem(at: idx, at: .bottom, animated: true)
})
}

Answer 1

Animation of IUCollectionView elements insertion and deletion is correctly done using finalLayoutAttributesForDisappearingItem(at:) and initialLayoutAttributesForAppearingItem(at:)
Little excerpt from Apple's documentation on finalLayoutAttributesForDisappearingItem(at:)
This method is called after the prepare(forCollectionViewUpdates:) method and before the finalizeCollectionViewUpdates() method for any items that are about to be deleted. Your implementation should return the layout information that describes the final position and state of the item. The collection view uses this information as the end point for any animations. (The starting point of the animation is the item’s current location.) If you return nil, the layout object uses the same attributes for both the start and end points of the animation.

Answer 2

I solved the problem by removing performBatchUpdates ... I have no idea why it works now and what exactly performBatchUpdates does but it works so if anyone wants to explain it to me, feel free :D
The final function looks like this:
func dismissWishlistVC(dataArray: [Wishlist], dropDownArray: [DropDownOption], shouldDeleteWithAnimation: Bool, indexToDelete: Int) {
if shouldDeleteWithAnimation {
self.shouldAnimateCells = true
self.dataSourceArray.remove(at: self.currentWishListIDX)
self.dropOptions.remove(at: self.currentWishListIDX)
// reload the collection view
theCollectionView.reloadData()
} else {
self.shouldAnimateCells = false
self.dataSourceArray = dataArray
self.dropOptions = dropDownArray
// reload the collection view
theCollectionView.reloadData()
theCollectionView.performBatchUpdates(nil, completion: nil)
}
self.makeWishView.dropDownButton.dropView.tableView.reloadData()
}