How to add an extra static cell to a Diffable Data Source? - swift

Question

With reference to this question, I would like to do something similar. There were two ways I tried to replicate the answer for my diffable data source for my collection view.
The first way was to create another diffable data source but for the same collection view. The actual item cells would be configured when the indexpath.row is less than the count of my array while when it is equals to the count, then it will display my static cell.
//configure cells: categoryCollectionViewDataSource is the actual datasource for the items that I want to display.
categoryCollectionViewDataSource = UICollectionViewDiffableDataSource<Int, MistakeCategory>(collectionView: categoryCollectionView){
(collectionView, indexPath, mistakeCategory) in
if indexPath.row < (subjectSelected?.MistakeCategories.count)! {
let cell = self.categoryCollectionView.dequeueReusableCell(withReuseIdentifier: "CategoryCollectionViewCell", for: indexPath) as! CategoryCollectionViewCell
cell.setProperty(SubjectCategory: nil, MistakeCategory: self.subjectSelected?.MistakeCategories[indexPath.row])
return cell
} else {
return nil
}
}
//configure cells: staticCollectionViewDataSource is the data source for the cell that I want to display no matter what. it is displayed at the last row of the indexpath.
staticCellCollectionViewDataSource = UICollectionViewDiffableDataSource<Int, Int>(collectionView: categoryCollectionView){
(collectionView, indexPath, mistakeCategory) in
if indexPath.row == subjectSelected?.MistakeCategories.count {
let cell = self.categoryCollectionView.dequeueReusableCell(withReuseIdentifier: "StaticCreateNewCategoryCollectionViewCell", for: indexPath) as! StaticCreateNewCategoryCollectionViewCell
return cell
} else {
return nil
}
}
And here is where I update my diffable data source which I run on my viewDidLoad after configuring my cells:
internal func updateCategoryCollectionView() {
var snapshot = NSDiffableDataSourceSnapshot<Int, MistakeCategory>()
snapshot.appendSections([0])
snapshot.appendItems(Array(subjectSelected!.MistakeCategories))
categoryCollectionViewDataSource.apply(snapshot) //error: 'attempt to insert section 0 but there are only 0 sections after the update'
var staticSnapshot = NSDiffableDataSourceSnapshot<Int,Int>()
staticSnapshot.appendSections([0])
staticSnapshot.appendItems([0])
staticCellCollectionViewDataSource.apply(staticSnapshot)
}
This results in the error 'attempt to insert section 0 but there are only 0 sections after the update'. I have tried to implement the functions of UICollectionViewDataSource but ran into the problem of how I can merge these two type of data sources.
As such, I am at a lost to what I can do to create a static custom cell at the end of my row.

Answer 1

I had the same problem with diffable data sources. Instead of creating a different data source and snapshot, I solved it by appending a default [AnyHashable] data to my snapshot where the static cell was wanted. In your case it would be after you append your usual MistakeCategories data.
To do this you need to initialize your data source as
categoryCollectionViewDataSource = UICollectionViewDiffableDataSource<Int, AnyHashable>(collectionView: categoryCollectionView){
(collectionView, indexPath, dataItem) in
and when using the dataItem object you need to cast
if let mistakeCategory = dataItem as? MistakeCategory {
// return your default cell here
}
and after the MistakeCategory cells
if indexPath.row == subjectSelected?.MistakeCategories.count {
let cell = self.categoryCollectionView.dequeueReusableCell(withReuseIdentifier: "StaticCreateNewCategoryCollectionViewCell", for: indexPath) as! StaticCreateNewCategoryCollectionViewCell
return cell
}
And finally when you apply your snapshot, you also need to use it as
var snapshot = NSDiffableDataSourceSnapshot<Int, AnyHashable>()
snapshot.appendSections([0])
snapshot.appendItems(Array(subjectSelected!.MistakeCategories))
//append your static value here
snapshot.appendItems([AnyHashable(0)])
categoryCollectionViewDataSource.apply(snapshot)
Disclaimer: This is an extremely hard-coded solution and I am looking for more elegant methods to do this, but I couldn't find any yet.

Answer 2

DiffableDataSource accepts enums for item and/or section. This allows you to easily have as many cell and section types as you need - just define them in an enum, register cells for them, and then point datasource to the right cell based on the enum value passed in.
The example below only has two types of items and one section, but you can use the same idea for different section types as well.
//Define as many types of items as you need
enum CollectionViewItem: Hashable {
case actualItem(ActualItem.ID) //You must to have a unique associated value if you want the datasource to be able to differentiate items. In this case I'm just using the item ID.
case staticButtonItem
}
//Register cells for each type of item
actualItemCellRegistration = UICollectionView.CellRegistration<YourDesiredCellTypeHere, CollectionViewItem> { (cell, indexPath, item) in
//Register cell
}
staticButtonCellRegistration = UICollectionView.CellRegistration<YourDesiredCellTypeHere, CollectionViewItem> { (cell, indexPath, item) in
//Register cell
}
//Point the datasource at the right registration based on the enum case
dataSource = UICollectionViewDiffableDataSource<Int, CollectionViewItem>(collectionView: collectionView){ (collectionView, indexPath, item) in
switch item {
case .actualItem:
return collectionView.dequeueConfiguredReusableCell(using: actualItemCellRegistration, for: indexPath, item: item)
case .staticButtonItem:
return collectionView.dequeueConfiguredReusableCell(using: staticButtonCellRegistration, for: indexPath, item: item)
}
}
//Make your snapshot with your defined items
func makeNewSnapshot(with data: [YourDataType]) {
var snapshot = NSDiffableDataSourceSnapshot<Int, CollectionViewItem>()
//Add your single section
snapshot.appendSections([0])
//Add your static cell
snapshot.appendItems(CollectionViewItem.staticButtonItem, toSection: 0)
//Add your actual items
let itemsForView = data.map {CollectionViewItem.actualItem($0.ID)}
snapshot.appendItems(itemsForView, toSection: 0)
dataSource.apply(snapshot)
}