Here’s to the crazy ones…

Introduction

At WWDC 2019 Apple introduced amazing APIs for UITableView and UICollectionView data management. For instance, the barely documented UITableViewDiffableDataSource can be used as a data source of a table view, and all modifications made to its NSDiffableDataSourceSnapshot are automatically applied by that table view.

Watch the official video “Advances in UI Data Sources” to get a better idea.

These diffable APIs were fantastic news for UIKit Developers. Unfortunately AppKit has got only NSCollectionViewDiffableDataSource and NSTableViewDiffableDataSource which means that NSOutlineView is out of luck. Let’s hope that Apple releases NSOutlineViewDiffableDataSource at WWDC21.

OutlineViewDiffableDataSource

This Swift Package is my modest attempt to implement a diffable data source for NSOutlineView with support for nested items. This is how it’s used:

let dataSource = OutlineViewDiffableDataSource (outlineView: outlineView)
var snapshot = dataSource.snapshot()
snapshot.appendItems([folder1, folder2])
snapshot.appendItems([file11, file12], into: folder1)
snapshot.appendItems([file21, file22], into: folder2)
dataSource.applySnapshot(initialSnapshot, animatingDifferences: false)

The accompanying DiffableDataSourceSnapshot API is heavily inspired by Cocoa’s own NSDiffableDataSourceSnapshot and includes many similar methods, but adopted for tree data structures:

// …
mutating func insertItems(_ newItems: [Item], beforeItem: Item) -> Bool
mutating func insertItems(_ newItems: [Item], afterItem: Item) -> Bool
mutating func deleteItems(_ existingItems: [Item]) -> Bool
mutating func deleteAllItems()
mutating func reloadItems(_ items: [Item]) -> Bool
// …

Not sure how this ends, but the DiffableDataSourceSnapshot is a value type. Just like its “official” counterpart, this struct can be built and applied from the background thread, as far as I know 😅

Demo App

The Demo Mac app is a playground for breaking the library. The snapshot API is 100% covered by Tests, but I would much appreciate any help with QA.

Help Wanted

If you download and play with the sample app, it’s already cool. But if you report or even fix one of the issues, you are just awesome. Here is a Roadmap, please join me if you can:

• Add a new section “Quick Start”
• Explain the protocol OutlineViewItem
• Explain how to implement drag-n-drop in your app
• Add versioning because now it’s just a master branch
• Add this project to the Dave’s repository of Swift Packages
• Improve the Demo app, it’s too basic and doesn’t show all the features
• File a Radar requesting a real NSOutlineViewDiffableDataSource, why not
• Make a profile picture from one of WWDC slides about diffable data sources
• Generate documentation using Swift Doc
• Add badges like “Swift 5.2” and “CI Passing”
• Fill the Community Profile
• Add Showcase section if anyone uses this component

Contact Information

You can always find me as @VadimShpakovski in Twitter. If you publish apps in the App Store or in the Mac App Store, check out my native client for the App Store Connect: NativeConnect. Some people like it. Thanks in advance!