WWDC19

Table of Contents

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• Advances In UI Data Sources - Wednesday
  • Current State-of-the-Art
  • A New Approach
    • Diffable Data Source
  • Considerations
    • Constructing Snapshots
    • Configuring Snapshots
    • Identifiers
    • What About IndexPath based APIs?
    • Performance

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

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

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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