How you can create reusable views for contemporary assortment views?

Reusable views inside a generic cell

All of us like to create customized views for constructing numerous person interface components, proper? We additionally love to make use of assortment views to show information utilizing a grid or a listing structure. Assortment view cells are customized views, however what if you would like to make use of the very same cell as a view?

Seems which you could present your personal UIContentConfiguration, identical to the built-in ones that you need to use to setup cells to appear to be listing objects. For those who check out the fashionable assortment views pattern code, which I extremely suggest, you may see implement customized content material configurations with the intention to create your personal cell varieties. There are some things that I do not like about this strategy. 😕

To begin with, your view has to evolve to the UIContentView protocol, so you need to deal with extra config associated stuff contained in the view. I desire the MVVM sample, so this feels a bit unusual. The second factor that you simply want is a customized cell subclass, the place you additionally should care for the configuration updates. What if there was another manner?

Let’s begin our setup by creating a brand new subclass for our future cell object, we’re merely going to offer the same old initialize methodology that I all the time use for my subclasses. Apple usually calls this methodology configure of their samples, however they’re roughly the identical. 😅

import UIKit

open class CollectionViewCell: UICollectionViewCell {
        
    @obtainable(*, unavailable)
    non-public override init(body: CGRect) {
        tremendous.init(body: body)
        
        self.initialize()
    }

    @obtainable(*, unavailable)
    public required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder) isn not obtainable")
    }
    
    open func initialize() {
        
    }

}

All proper, that is only a fundamental subclass so we do not have to take care of the init strategies anymore. Let’s create yet one more subclass based mostly on this object. The ReusableCell sort goes to be a generic sort, it may have a view property, which goes to be added as a subview to the contentView and we additionally pin the constraints to the content material view.

import UIKit

open class ReusableCell<View: UIView>: CollectionViewCell {
    
    var view: View!

    open override func initialize() {
        tremendous.initialize()

        let view = View()
        view.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(view)
        self.view = view
        
        NSLayoutConstraint.activate([
            view.topAnchor.constraint(equalTo: contentView.topAnchor),
            view.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
            view.leadingAnchor.constraint(equalTo: contentView.leadingAnchor),
            view.trailingAnchor.constraint(equalTo: contentView.trailingAnchor),
        ])
    }
}

Through the use of this reusable cell sort, it may be potential so as to add a customized view to the cell. We simply must create a brand new customized view, however that is fairly a simple process to do. ✅

import UIKit

extension UIColor {

    static var random: UIColor {
        .init(pink: .random(in: 0...1),
              inexperienced: .random(in: 0...1),
              blue: .random(in: 0...1),
              alpha: 1)
    }
}

class CustomView: View {

    let label = UILabel(body: .zero)

    override func initialize() {
        label.translatesAutoresizingMaskIntoConstraints = false
        label.numberOfLines = 0
        addSubview(label)
        
        
        backgroundColor = .random

        NSLayoutConstraint.activate([
            
            label.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 8),
            label.trailingAnchor.constraint(equalTo: trailingAnchor, constant: -8),
            label.topAnchor.constraint(equalTo: topAnchor, constant: 8),
            label.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -8),
        ])
    }

}

This tradition view has a label, which we will pin to the superview with some additional padding. You possibly can retailer all of your subviews as sturdy properties, since Apple goes to care for the deinit, although the addSubview creates a robust reference, you do not have to fret about it anymore.

If you wish to create a cell that helps dynamic top, it’s best to merely pin the sting structure constraints, however if you would like to make use of a set top cell you’ll be able to add your personal top anchor constraint with a continuing worth. You need to set a customized precedence for the peak constraint this manner the auto structure system will not break and it is going to have the ability to fulfill all the required constraints.

Compositional structure fundamentals

The UICollectionViewCompositionalLayout class is a extremely adaptive and versatile structure device that you need to use to construct fashionable assortment view layouts. It has three most important elements which you could configure to show your customized person interface components in many alternative methods.

You mix the elements by increase from objects into a gaggle, from teams into a piece, and at last right into a full structure,
like on this instance of a fundamental listing structure:

There are many nice sources and tutorials about this subject, so I will not get an excessive amount of into the small print now, however we will create a easy structure that may show full width (fractional structure dimension) objects in a full width group, through the use of and estimated top to assist dynamic cell sizes. I suppose that is fairly a typical use-case for many people. We will create an extension on the UICollectionViewLayout object to instantiate a brand new listing structure. 🙉

extension UICollectionViewLayout {
    static func createListLayout() -> UICollectionViewLayout {
        let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .estimated(44))
        let merchandise = NSCollectionLayoutItem(layoutSize: itemSize)
      
        let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .estimated(44))
        let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item])
        let part = NSCollectionLayoutSection(group: group)

        let structure = UICollectionViewCompositionalLayout(part: part)
        return structure
    }
}

Now it’s potential so as to add a collectionView to our view hierarchy contained in the view controller.

class ViewController: UIViewController {

    let collectionView = UICollectionView(body: .zero, collectionViewLayout: .createListLayout())

    override func loadView() {
        tremendous.loadView()

        collectionView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(collectionView)
        NSLayoutConstraint.activate([
            view.topAnchor.constraint(equalTo: collectionView.topAnchor),
            view.bottomAnchor.constraint(equalTo: collectionView.bottomAnchor),
            view.leadingAnchor.constraint(equalTo: collectionView.leadingAnchor),
            view.trailingAnchor.constraint(equalTo: collectionView.trailingAnchor),
        ])
    }

    override func viewDidLoad() {
        tremendous.viewDidLoad()

    }
}

You may also create your personal auto structure helper extensions, or use SnapKit to shortly setup your structure constraints. It’s comparatively straightforward to work with anchors, it’s best to learn my different tutorial about mastering auto structure anchors if you do not know a lot about them.

Cell registration and diffable information supply

Apple has a new set of APIs to register and dequeue cells for contemporary assortment views. It’s value to say that just about every little thing we speak about this tutorials is just obtainable on iOS14+ so if you’re planning to assist an older model you will not be capable of use these options.

If you wish to be taught extra concerning the subject, I might wish to suggest an article by Donny Wals and there’s a nice, however a bit longer publish by John Sundell about fashionable assortment views. I am utilizing the identical helper extension to get a cell supplier utilizing a cell registration object, to make the method extra easy, plus we will want some random sentences, so let’s add a couple of helpers. 💡

extension String {
    static func randomWord() -> String {
        (0..<Int.random(in: 1...10)).map { _ in String(format: "%c", Int.random(in: 97..<123)) }.joined(separator: "")
    }

    static func randomSentence() -> String {
        (0...50).map { _ in randomWord() }.joined(separator: " ")
    }
}


extension UICollectionView.CellRegistration {

    var cellProvider: (UICollectionView, IndexPath, Merchandise) -> Cell {
        { collectionView, indexPath, product in
            collectionView.dequeueConfiguredReusableCell(utilizing: self, for: indexPath, merchandise: product)
        }
    }
}

Now we will use the brand new UICollectionViewDiffableData class to specify our sections and objects inside the gathering view. You possibly can outline your sections as an enum, and on this case we will use a String sort as our objects. There’s a nice tutorial by AppCoda about diffable information sources.

Lengthy story brief, it’s best to make a brand new cell configuration the place now you need to use the ReusableCell with a CustomView, then it’s potential to setup the diffable information supply with the cellProvider on the cellRegistration object. Lastly we will apply an preliminary snapshot by appending a brand new part and our objects to the snapshot. You possibly can replace the information supply with the snapshot and the good factor about is it which you could additionally animate the modifications if you need. 😍

enum Part {
    case `default`
}

class ViewController: UIViewController {

    let collectionView = UICollectionView(body: .zero, collectionViewLayout: .createListLayout())
    var dataSource: UICollectionViewDiffableDataSource<Part, String>!
    let information: [String] = (0..<10).map { _ in String.randomSentence() }

    override func loadView() {
        tremendous.loadView()

        collectionView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(collectionView)
        NSLayoutConstraint.activate([
            view.topAnchor.constraint(equalTo: collectionView.topAnchor),
            view.bottomAnchor.constraint(equalTo: collectionView.bottomAnchor),
            view.leadingAnchor.constraint(equalTo: collectionView.leadingAnchor),
            view.trailingAnchor.constraint(equalTo: collectionView.trailingAnchor),
        ])
    }

    override func viewDidLoad() {
        tremendous.viewDidLoad()

        collectionView.delegate = self

        createDataSource()
        applyInitialSnapshot()
    }

    func createDataSource() {
        let cellRegistration = UICollectionView.CellRegistration<ReusableCell<CustomView>, String> { cell, indexPath, mannequin in
            cell.view.label.textual content = mannequin
        }

        dataSource = UICollectionViewDiffableDataSource<Part, String>(collectionView: collectionView,
                                                                         cellProvider: cellRegistration.cellProvider)
    }
    
    func applyInitialSnapshot() {
        var snapshot = NSDiffableDataSourceSnapshot<Part, String>()
        snapshot.appendSections([.default])
        snapshot.appendItems(information)
        dataSource.apply(snapshot, animatingDifferences: true)
    }
}

extension ViewController: UICollectionViewDelegate {

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let merchandise = dataSource.itemIdentifier(for: indexPath)

        print(merchandise ?? "n/a")
    }
}

You continue to should implement a delegate methodology if you would like to deal with cell choice, however thankfully the diffable information supply has an itemIdentifier methodology to lookup components inside the information supply.

As you’ll be able to see it is fairly straightforward to provide you with a generic cell that can be utilized to render a customized view inside a group view. I imagine that the “official” cell configuration based mostly strategy is a little more sophisticated, plus you need to write numerous code if it involves fashionable assortment views.

I will replace my authentic assortment view framework with these new strategies for positive. The brand new compositional structure is far more highly effective in comparison with common circulate layouts, diffable information sources are additionally wonderful and the brand new cell registration API can also be good. I imagine that the gathering view crew at Apple did an incredible job throughout the years, it is nonetheless one in every of my favourite elements if it involves UIKit improvement. I extremely suggest studying these fashionable strategies. 👍