ArrayUpdater

• Overview
• Usage
  • Serialization
  • Archiving
  • Caching
• Installation

Overview

ArrayUpdater is a framework for calculating the insertions, deletions, and reloads needed to update one array to another. Its main use case is to simply the process of updating table and collection views when the data they are presenting changes. The framework returns a struct containing the required insertions, deletions, and reloads, as well as a convenience function to map them to index paths. These index paths can then be used directly in begin/end updates calls (table views) or performBatchUpdates calls (collection views).

Usage

Protocol Requirements

Code

struct Park: Updatable {

    let id: String
    let name: String

}

Explanation

In order for ArrayUpdater to calculate insertions and deletions, types must conform to the Equatable protocol. However, the framework also needs some way to know when an object or value is equal but updated in a meaningful way (reloads).

ArrayUpdater provides the Updatable protocol for this, which extends Hashable (which in turn extends Equatable. Updatable has one requirement, that types have an id property. Conforming types will implement Equatable, and the framework uses the equality check and the id property to determine which items in the array need to be updated in place.

Updating Arrays

Code

let arches = Park(id: "NPS01", name: "Arches")
let grandCanyon = Park(id: "NPS02", name: "Grand Canyon")
let greatSmoky = Park(id: "NPS03", name: "Great Smoky Mountains")
let greatSmoky2 = Park(id: "NPS03", name: "Great Smokies")
let yosemite = Park(id: "NPS04", name: "Yosemite")
let zion = Park(id: "NPS05", name: "Zion")

let parks1 = [arches, greatSmoky, yosemite, zion]
let parks2 = [zion, grandCanyon, greatSmoky2, yosemite, arches]

let update = parks1.update(to: parks2)
print(update)

Output

▿ Update
  ▿ reloads : 1 element
    - 0 : 1
  ▿ deletions : 2 elements
    - 0 : 0
    - 1 : 3
  ▿ insertions : 3 elements
    - 0 : 0
    - 1 : 1
    - 2 : 4

Explanation

Table and collection views perform updates in a certain order, with reloads and deletions occurring before insertions. Therefore, in the above example, let's start with the first array and see how we get to the second:

1. We have one reload at index 1. "greatSmoky" and "greatSmoky2" are equal because their ids are equal, but their names do not match, so this item needs to be reloaded. Since reloads and deletions happen before insertions, this reload happens with respect to its index in the first array, which is 1.
2. We have two deletions, at indices 0 and 3. Again, deletions occur before insertions. In our example "arches" and "zion" have changed position, and therefore need to be deleted before being reinserted at their new positions.
3. At this point our array is [greatSmoky2, yosemite]. In order to get to parks2, we need to insert "zion", "grandCanyon", and "arches" at indices 0, 1, and 4, respectively.

For more information, see the section Ordering of Operations and Index Paths in the Apple documentation here.

Table & Collection Views

Code

parks = parks1
let update = parks1.update(to: parks2)
parks = parks2

let reloads = update.reloads.indexPaths(inSection: 0)
let deletions = update.deletions.indexPaths(inSection: 0)
let insertions = update.insertions.indexPaths(inSection: 0)

// Table View
tableView.beginUpdates()
tableView.reloadRows(at: reloads, with: .automatic)
tableView.deleteRows(at: deletions, with: .automatic)
tableView.insertRows(at: insertions, with: .automatic)
tableView.endUpdates()

// Collection View
collectionView.performBatchUpdates({ 
    self.collectionView.reloadItems(at: reloads)
    self.collectionView.deleteItems(at: deletions)
    self.collectionView.insertItems(at: insertions)
}, completion: nil)

Explanation

The parks variable represents our data source and is set initially to the original data, parks1. ArrayUpdater then calculates the updates, and parks is set to parks2 before the table or collection view updates begin. Table / collection view updates must happen after the underlying data source has been updated.

ArrayUpdater provides a convenience function for converting Int arrays (the reload, deletion, or insertion indices) to index paths. It includes a section parameter to support data sources with multiple sections. Here the data source only has one section, so the update indices are converted to their corresponding index paths in section 0.

Example Data Source

Code

class ParksTableViewDataSource: NSObject, UITableViewDataSource {

    private(set) var parks: [Park]

    init(parks: [Park]) {
        self.parks = parks
    }

    func update(with parks: [Park]) -> IndexUpdate {
        let update = self.parks.update(to: parks)
        self.parks = parks
        return update
    }

    func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return parks.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "ParkCell")!
        let park = parks[indexPath.row]
        cell.textLabel?.text = park.name
        
        return cell
    }

}

Explanation

The above is an example of how you might implement a table view data source using ArrayUpdater. The key part is the "update:with" function, which returns an IndexUpdate value containing the required reloads, deletions, and insertions. The function simply calculates the updates, replaces the underlying data, and returns the IndexUpdate value. Then the table view can animate the updates as described in Table & Collection Views.

Installation

Note: ArrayUpdater requires Swift 3 (and Xcode 8) or greater.

Targets using ArrayUpdater must support embedded Swift frameworks.

Swift Package Manager

Swift Package Manager is Apple's official package manager for Swift frameworks. To install with Swift Package Manager:

1. Add ArrayUpdater to your Package.swift file:

   import PackageDescription
   
   let package = Package(
       name: "MyAppTarget",
       dependencies: [
           .Package(url: "https://github.com/toddkramer/ArrayUpdater",
                    majorVersion: 1, minor: 4)
       ]
   )
   

2. Run swift build.

3. Generate Xcode project:

   swift package generate-xcodeproj
   

Carthage

Carthage is a decentralized dependency manager for Cocoa projects. To install ArrayUpdater with Carthage:

1. Make sure Carthage is installed.

2. Add ArrayUpdater to your Cartfile:

   github "toddkramer/ArrayUpdater" ~> 1.4.0
   

3. Run carthage update and add the appropriate framework.

CocoaPods

CocoaPods is a centralized dependency manager for Cocoa projects. To install ArrayUpdater with CocoaPods:

1. Make sure the latest version of CocoaPods is installed.

2. Add ArrayUpdater to your Podfile:

   use_frameworks!
   
   pod 'ArrayUpdater', '~> 1.4.0'
   

3. Run pod install.