How to move UITableView cells while using UITableViewDiffableDataSource?

Question

I am trying to make my tableView cells movable, but it needs 2 or 3 functions from UITableViewDataSource protocol, If I tried to implement the delegate in my viewController It will ask for numberOfRowsInSection and cellForRowAtIndexPath functions which are already covered by the new UITableViewDiffableDataSource.

How can I achieve this behavior while using the new UITableViewDiffableDataSource?

Answer 1

To flesh out Tung Fam's answer, here is a complete implementation:

class MovableTableViewDataSource: UITableViewDiffableDataSource<Int, Int> {

    override func tableView(_ tableView: UITableView, moveRowAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {
        super.tableView(tableView, moveRowAt: sourceIndexPath, to: destinationIndexPath)

        var snapshot = self.snapshot()
        if let sourceId = itemIdentifier(for: sourceIndexPath) {
            if let destinationId = itemIdentifier(for: destinationIndexPath) {
                guard sourceId != destinationId else {
                    return // destination is same as source, no move.
                }
                // valid source and destination
                if sourceIndexPath.row > destinationIndexPath.row {
                    snapshot.moveItem(sourceId, beforeItem: destinationId)
                } else {
                    snapshot.moveItem(sourceId, afterItem: destinationId)
                }
            } else {
                // no valid destination, eg. moving to the last row of a section
                snapshot.deleteItems([sourceId])
                snapshot.appendItems([sourceId], toSection: snapshot.sectionIdentifiers[destinationIndexPath.section])
            }
        }

        apply(snapshot, animatingDifferences: false, completion: nil)
    }
}

It will crash if animatingDifferences is set true (animating is not really desirable here anyway).

I'm not sure whether calling super.tableView(move…) is necessary, but it doesn't seem to do any harm.