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 an inventory 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 that you would be able to present your individual UIContentConfiguration, similar to the built-in ones that you should use to setup cells to seem like checklist gadgets. For those who check out the trendy assortment views pattern code, which I extremely advocate, you may see how you can implement customized content material configurations with the intention to create your individual cell sorts. There are some things that I do not like about this method. 😕

Initially, your view has to evolve to the UIContentView protocol, so you must deal with extra config associated stuff contained in the view. I choose 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 must 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 supply the same old initialize technique that I all the time use for my subclasses. Apple usually calls this technique configure of their samples, however they’re kind of the identical. 😅

import UIKit

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

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

}

All proper, that is only a primary subclass so we do not have to cope with the init strategies anymore. Let’s create another subclass primarily based on this object. The ReusableCell sort goes to be a generic sort, it’ll 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),
        ])
    }
}

By utilizing this reusable cell sort, it’ll be doable so as to add a customized view to the cell. We simply have to create a brand new customized view, however that is fairly a straightforward process to do. ✅

import UIKit

extension UIColor {

    static var random: UIColor {
        .init(purple: .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 practice view has a label, which we will pin to the superview with some further padding. You possibly can retailer all of your subviews as robust properties, since Apple goes to care for the deinit, although the addSubview creates a powerful reference, you do not have to fret about it anymore.

If you wish to create a cell that helps dynamic top, you need to merely pin the sting structure constraints, however if you would like to make use of a hard and fast top cell you possibly can add your individual top anchor constraint with a continuing worth. It’s a must 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 mandatory constraints.

Compositional structure fundamentals

The UICollectionViewCompositionalLayout class is a extremely adaptive and versatile structure device that you should use to construct trendy assortment view layouts. It has three fundamental parts that you would be able to configure to show your customized person interface components in many alternative methods.

You mix the parts by increase from gadgets into a bunch, from teams into a bit, and eventually right into a full structure,
like on this instance of a primary checklist structure:

There are many nice assets and tutorials about this matter, 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) gadgets in a full width group, by utilizing and estimated top to assist dynamic cell sizes. I suppose that is fairly a standard use-case for many people. We are able to create an extension on the UICollectionViewLayout object to instantiate a brand new checklist 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 doable 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 can even create your individual auto structure helper extensions, or use SnapKit to shortly setup your structure constraints. It’s comparatively simple to work with anchors, you need 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 nearly every little thing we speak about this tutorials is just out there on iOS14+ so if you’re planning to assist an older model you will not be capable to use these options.

If you wish to be taught extra in regards to the matter, I might prefer to advocate an article by Donny Wals and there’s a nice, however a bit longer submit by John Sundell about trendy 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 number 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 gadgets 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 gadgets. There’s a nice tutorial by AppCoda about diffable information sources.

Lengthy story quick, you need to make a brand new cell configuration the place now you should use the ReusableCell with a CustomView, then it’s doable 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 gadgets to the snapshot. You possibly can replace the information supply with the snapshot and the good factor about is it that you would be able to 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 must implement a delegate technique if you would like to deal with cell choice, however happily the diffable information supply has an itemIdentifier technique to lookup components inside the information supply.

As you possibly can see it is fairly simple to provide you with a generic cell that can be utilized to render a customized view inside a set view. I consider that the “official” cell configuration primarily based method is a little more sophisticated, plus you must write numerous code if it involves trendy assortment views.

I’ll 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 movement layouts, diffable information sources are additionally superb and the brand new cell registration API can be good. I consider that the gathering view staff at Apple did a tremendous job through the years, it is nonetheless considered one of my favourite parts if it involves UIKit improvement. I extremely advocate studying these trendy strategies. 👍