Get SectionIdentifier from DiffableDataSource using IndexPath

Question

Created Jan ’20

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When using either UICollectionViewDiffableDataSource or UITableViewDiffableDataSource, what is the "correct/safe" way to get the section identifier from an index path?

snapshot().sectionIdentifiers[indexPath.section]

or

guard let item = itemIdentifier(for: indexPath) else { return }
snapshot().sectionIdentifier(containingItem: item)

?

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Answer 1

Claude31 OP

Jan ’20

As far as I can tell, first is correct.

For the second, could it be that itemIdentifier(for: indexPath) be nil if section is empty ?

Not such a risk with the first

May look at this tutorial:

h ttps://medium.com/@jamesrochabrun/uicollectionviewdiffabledatasource-and-decodable-step-by-step-6b727dd2485

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Answer 2

Miguelonce OP

Apr ’20

/* See LICENSE folder for this sample’s licensing information. Abstract: This sample's application delegate. */ import Cocoa @NSApplicationMain class AppDelegate: NSObject, NSApplicationDelegate { }

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Answer 3

John.liedtke OP

Feb ’21

I'd love for this operation to be O(1) like itemIdentifier(for:):

This method is a constant time operation, O(1), which means you can look up an item identifier from its corresponding index path with no significant overhead.

I fear, perhaps unnecessarily, that snapshot() is an O(n) operation meaning retrieving the section identifier turns into an expensive operation.

Can someone from Apple chime in here?

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