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advances_in_ui_data_sources.md

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WWDC19

Table of Contents

=================

Advances In UI Data Sources - Wednesday

Session materials: https://developer.apple.com/videos/play/wwdc2019/220/

Current State-of-the-Art

  • Traditional UICollectionViewDataSource
    • Simple & flexible
  • Generating UI Updates can be challenging
    • Current approach which relies on informing the UI and updating is error prone
    • There is no centralized truth

A New Approach

Diffable Data Source

  • performBatchUpdates() is gone, apply() is the new cool kid in town!
  • Applying a snapshot via UICollectionViewDiffableDataSource & UITableViewDiffableDataSource
  • Call it anytime the UI requires a change
let snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
snapshot.appendSections([.aSection])
snapshot.appendItems(items, toSection: aSection)
// delete, modify etc. is also available

======================

self.dataSource = UITableViewDiffableDataSource<Section, Item>(tableView: tableView) {
  // the code we usually execute at cellForRowAtIndexPath to reflect changes
}

======================

datasource.apply(snapshot)

Considerations

  • Always call apply(), never call performBatchUpdates() ,insertItems()

Constructing Snapshots

  • Empty
    • let snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
  • Current data source snapshot copy
    • datasource.snapshot()

Configuring Snapshots

  • insertItems(_ identifiers: [ItemIdentifierType], beforeItem beforeIdentifier: ItemIdentifierType)
  • moveItems
  • appendItems
  • appendSections

Identifiers

  • Must be unique
  • Conforms to Hashable
  • Data model or identifier

What About IndexPath based APIs?

  • e.g: didSelectItemAt indexpath should be converted to the datasource snapshot selection

Performance

  • Safe to call apply() from a bg thread

    • But, always call from the main queue or a bg queue, don't mix and match

  • The newly designed share sheet on iOS13 uses this new implementation