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Working with diffable knowledge sources and desk views utilizing UIKit


Mission setup

We’ll use a daily storyboard-based Xcode undertaking, since we’re working with UIKit.


We’re additionally going to want a desk view, for this goal we may go along with a conventional setup, however since we’re utilizing trendy UIKit practices we will do issues only a bit totally different this time.


It is fairly unlucky that we nonetheless have to offer our personal type-safe reusable extensions for UITableView and UICollectionView lessons. Anyway, here is a fast snippet that we’ll use. ⬇️


import UIKit

extension UITableViewCell {
    
    static var reuseIdentifier: String {
        String(describing: self)
    }

    var reuseIdentifier: String {
        kind(of: self).reuseIdentifier
    }
}

extension UITableView {
        
    func register<T: UITableViewCell>(_ kind: T.Sort) {
        register(T.self, forCellReuseIdentifier: T.reuseIdentifier)
    }

    func reuse<T: UITableViewCell>(_ kind: T.Sort, _ indexPath: IndexPath) -> T {
        dequeueReusableCell(withIdentifier: T.reuseIdentifier, for: indexPath) as! T
    }
}


I’ve additionally created a subclass for UITableView, so I can configure every thing contained in the initialize operate that we will want on this tutorial.


import UIKit

open class TableView: UITableView {

    public init(type: UITableView.Fashion = .plain) {
        tremendous.init(body: .zero, type: type)
        
        initialize()
    }

    @accessible(*, unavailable)
    required public init?(coder: NSCoder) {
        fatalError("init(coder:) has not been carried out")
    }
    
    open func initialize() {
        translatesAutoresizingMaskIntoConstraints = false
        allowsMultipleSelection = true
    }
    
    func layoutConstraints(in view: UIView) -> [NSLayoutConstraint] {
        [
            topAnchor.constraint(equalTo: view.topAnchor),
            bottomAnchor.constraint(equalTo: view.bottomAnchor),
            leadingAnchor.constraint(equalTo: view.leadingAnchor),
            trailingAnchor.constraint(equalTo: view.trailingAnchor),
        ]
    }
}


We’re going to construct a settings display with a single choice and a a number of choice space, so it is good to have some extensions too that’ll assist us to handle the chosen desk view cells. 💡


import UIKit

public extension UITableView {
    
    func choose(_ indexPaths: [IndexPath],
                animated: Bool = true,
                scrollPosition: UITableView.ScrollPosition = .none) {
        for indexPath in indexPaths {
            selectRow(at: indexPath, animated: animated, scrollPosition: scrollPosition)
        }
    }
    

    func deselect(_ indexPaths: [IndexPath], animated: Bool = true) {
        for indexPath in indexPaths {
            deselectRow(at: indexPath, animated: animated)
        }
    }
    
    func deselectAll(animated: Bool = true) {
        deselect(indexPathsForSelectedRows ?? [], animated: animated)
    }

    func deselectAllInSection(besides indexPath: IndexPath) {
        let indexPathsToDeselect = (indexPathsForSelectedRows ?? []).filter {
            $0.part == indexPath.part && $0.row != indexPath.row
        }
        deselect(indexPathsToDeselect)
    }
}


Now we will give attention to making a customized cell, we’re going to use the brand new cell configuration API, however first we want a mannequin for our customized cell class.


import Basis

protocol CustomCellModel {
    var textual content: String { get }
    var secondaryText: String? { get }
}

extension CustomCellModel {
    var secondaryText: String? { nil }
}


Now we will use this cell mannequin and configure the CustomCell utilizing the mannequin properties. This cell could have two states, if the cell is chosen we will show a stuffed examine mark icon, in any other case simply an empty circle. We additionally replace the labels utilizing the summary mannequin values. ✅


import UIKit

class CustomCell: UITableViewCell {

    var mannequin: CustomCellModel?

    override func updateConfiguration(utilizing state: UICellConfigurationState) {
        tremendous.updateConfiguration(utilizing: state)
        
        var contentConfig = defaultContentConfiguration().up to date(for: state)
        contentConfig.textual content = mannequin?.textual content
        contentConfig.secondaryText = mannequin?.secondaryText
        
        contentConfig.imageProperties.tintColor = .systemBlue
        contentConfig.picture = UIImage(systemName: "circle")

        if state.isHighlighted || state.isSelected {
            contentConfig.picture = UIImage(systemName: "checkmark.circle.fill")
        }
        contentConfiguration = contentConfig
    }
}


Contained in the ViewController class we will simply setup the newly created desk view. Since we’re utilizing a storyboard file we will override the init(coder:) technique this time, however if you’re instantiating the controller programmatically then you may merely create your individual init technique.


By the way in which I additionally wrapped this view controller inside a navigation controller so I am show a customized title utilizing the big type by default and there are some lacking code items that we now have to put in writing.


import UIKit

class ViewController: UIViewController {
    
    var tableView: TableView
    
    required init?(coder: NSCoder) {
        self.tableView = TableView(type: .insetGrouped)

        tremendous.init(coder: coder)
    }
    
    override func loadView() {
        tremendous.loadView()
        
        view.addSubview(tableView)

        NSLayoutConstraint.activate(tableView.layoutConstraints(in: view))
    }

    override func viewDidLoad() {
        tremendous.viewDidLoad()
        
        title = "Desk view"
        navigationController?.navigationBar.prefersLargeTitles = true

        tableView.register(CustomCell.self)
        tableView.delegate = self

    }
    
    override func viewDidAppear(_ animated: Bool) {
        tremendous.viewDidAppear(animated)
        
        reload()
    }
    
    func reload() {
        
    }

}

extension ViewController: UITableViewDelegate {

    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        
    }

    func tableView(_ tableView: UITableView, didDeselectRowAt indexPath: IndexPath) {
        
    }
}


We do not have to implement the desk view knowledge supply strategies, however we will use a diffable knowledge supply for that goal, let me present you the way it works.




Diffable knowledge supply


I’ve already included one instance containing a diffable knowledge supply, however that was a tutorial for creating trendy assortment views. A diffable knowledge supply is actually a knowledge supply tied to a view, in our case the UITableViewDiffableDataSource generic class goes to behave as a knowledge supply object 4 our desk view. The great take into consideration these knowledge sources is which you could simply manipulate the sections and rows contained in the desk view with out the necessity of working with index paths.


So the primary concept right here is that we might wish to show two sections, one with a single choice possibility for choosing a quantity, and the second possibility group goes to include a multi-selection group with some letters from the alphabet. Listed below are the information fashions for the part objects.


enum NumberOption: String, CaseIterable {
    case one
    case two
    case three
}

extension NumberOption: CustomCellModel {
 
    var textual content: String { rawValue }
}

enum LetterOption: String, CaseIterable {
    case a
    case b
    case c
    case d
}

extension LetterOption: CustomCellModel {
 
    var textual content: String { rawValue }
}


Now we must always be capable to show this stuff contained in the desk view, if we implement the common knowledge supply strategies, however since we will work with a diffable knowledge supply we want some further fashions. To get rid of the necessity of index paths, we will use a Hashable enum to outline our sections, we will have two sections, one for the numbers and one other for the letters. We’ll wrap the corresponding kind inside an enum with type-safe case values.


enum Part: Hashable {
    case numbers
    case letters
}

enum SectionItem: Hashable {
    case quantity(NumberOption)
    case letter(LetterOption)
}

struct SectionData {
    var key: Part
    var values: [SectionItem]
}


We’re additionally going to introduce a SectionData helper, this manner it may be easier to insert the required sections and part objects utilizing the information supply.


remaining class DataSource: UITableViewDiffableDataSource<Part, SectionItem> {
    
    init(_ tableView: UITableView) {
        tremendous.init(tableView: tableView) { tableView, indexPath, itemIdentifier in
            let cell = tableView.reuse(CustomCell.self, indexPath)
            cell.selectionStyle = .none
            change itemIdentifier {
            case .quantity(let mannequin):
                cell.mannequin = mannequin
            case .letter(let mannequin):
                cell.mannequin = mannequin
            }
            return cell
        }
    }
    
    override func tableView(_ tableView: UITableView, titleForHeaderInSection part: Int) -> String? {
        let id = sectionIdentifier(for: part)
        change id {
        case .numbers:
            return "Decide a quantity"
        case .letters:
            return "Decide some letters"
        default:
            return nil
        }
    }

    func reload(_ knowledge: [SectionData], animated: Bool = true) {
        var snapshot = snapshot()
        snapshot.deleteAllItems()
        for merchandise in knowledge {
            snapshot.appendSections([item.key])
            snapshot.appendItems(merchandise.values, toSection: merchandise.key)
        }
        apply(snapshot, animatingDifferences: animated)
    }
}


We are able to present a customized init technique for the information supply, the place we will use the cell supplier block to configure our cells with the given merchandise identifier. As you’ll be able to see the merchandise identifier is definitely the SectionItem enum that we created a couple of minutes in the past. We are able to use a change to get again the underlying mannequin, and since these fashions conform to the CustomCellModel protocol we will set the cell.mannequin property. It is usually attainable to implement the common titleForHeaderInSection technique and we will change the part id and return a correct label for every part.


The ultimate technique is a helper, I am utilizing it to reload the information supply with the given part objects.


import UIKit

class ViewController: UIViewController {
    
    var tableView: TableView
    var dataSource: DataSource
    
    required init?(coder: NSCoder) {
        self.tableView = TableView(type: .insetGrouped)
        self.dataSource = DataSource(tableView)

        tremendous.init(coder: coder)
    }
    
    override func loadView() {
        tremendous.loadView()
        
        view.addSubview(tableView)

        NSLayoutConstraint.activate(tableView.layoutConstraints(in: view))
    }

    override func viewDidLoad() {
        tremendous.viewDidLoad()
        
        title = "Desk view"
        navigationController?.navigationBar.prefersLargeTitles = true

        tableView.register(CustomCell.self)
        tableView.delegate = self

    }
    
    override func viewDidAppear(_ animated: Bool) {
        tremendous.viewDidAppear(animated)
        
        reload()
    }
    
    func reload() {
        dataSource.reload([
            .init(key: .numbers, values: NumberOption.allCases.map { .number($0) }),
            .init(key: .letters, values: LetterOption.allCases.map { .letter($0) }),
        ])
    }

}

extension ViewController: UITableViewDelegate {

    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        
    }

    func tableView(_ tableView: UITableView, didDeselectRowAt indexPath: IndexPath) {
        
    }
}


So contained in the view controller it’s attainable to render the desk view and show each sections, even the cells are selectable by default, however I would like to point out you easy methods to construct a generic strategy to retailer and return chosen values, after all we may use the indexPathsForSelectedRows property, however I’ve slightly helper device which is able to permit single and a number of choice per part. 🤔


struct SelectionOptions<T: Hashable> {

    var values: [T]
    var selectedValues: [T]
    var multipleSelection: Bool

    init(_ values: [T], chosen: [T] = [], a number of: Bool = false) {
        self.values = values
        self.selectedValues = chosen
        self.multipleSelection = a number of
    }

    mutating func toggle(_ worth: T) {
        guard multipleSelection else {
            selectedValues = [value]
            return
        }
        if selectedValues.comprises(worth) {
            selectedValues = selectedValues.filter { $0 != worth }
        }
        else {
            selectedValues.append(worth)
        }
    }
}


Through the use of a generic extension on the UITableViewDiffableDataSource class we will flip the chosen merchandise values into index paths, this may assist us to make the cells chosen when the view masses.


import UIKit

extension UITableViewDiffableDataSource {

    func selectedIndexPaths<T: Hashable>(_ choice: SelectionOptions<T>,
                                         _ rework: (T) -> ItemIdentifierType) ->  [IndexPath] {
        choice.values
            .filter { choice.selectedValues.comprises($0) }
            .map { rework($0) }
            .compactMap { indexPath(for: $0) }
    }
}


There is just one factor left to do, which is to deal with the one and a number of choice utilizing the didSelectRowAt and didDeselectRowAt delegate strategies.


import UIKit

class ViewController: UIViewController {
    
    var tableView: TableView
    var dataSource: DataSource
    
    var singleOptions = SelectionOptions<NumberOption>(NumberOption.allCases, chosen: [.two])
    var multipleOptions = SelectionOptions<LetterOption>(LetterOption.allCases, chosen: [.a, .c], a number of: true)

    required init?(coder: NSCoder) {
        self.tableView = TableView(type: .insetGrouped)
        self.dataSource = DataSource(tableView)

        tremendous.init(coder: coder)
    }
    
    override func loadView() {
        tremendous.loadView()
        
        view.addSubview(tableView)

        NSLayoutConstraint.activate(tableView.layoutConstraints(in: view))
    }

    override func viewDidLoad() {
        tremendous.viewDidLoad()
        
        title = "Desk view"
        navigationController?.navigationBar.prefersLargeTitles = true

        tableView.register(CustomCell.self)
        tableView.delegate = self

    }
    
    override func viewDidAppear(_ animated: Bool) {
        tremendous.viewDidAppear(animated)
        
        reload()
    }
    
    func reload() {
        dataSource.reload([
            .init(key: .numbers, values: singleOptions.values.map { .number($0) }),
            .init(key: .letters, values: multipleOptions.values.map { .letter($0) }),
        ])

        tableView.choose(dataSource.selectedIndexPaths(singleOptions) { .quantity($0) })
        tableView.choose(dataSource.selectedIndexPaths(multipleOptions) { .letter($0) })
    }

}

extension ViewController: UITableViewDelegate {

    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        guard let sectionId = dataSource.sectionIdentifier(for: indexPath.part) else {
            return
        }

        change sectionId {
        case .numbers:
            guard case let .quantity(mannequin) = dataSource.itemIdentifier(for: indexPath) else {
                return
            }
            tableView.deselectAllInSection(besides: indexPath)
            singleOptions.toggle(mannequin)
            print(singleOptions.selectedValues)
            
        case .letters:
            guard case let .letter(mannequin) = dataSource.itemIdentifier(for: indexPath) else {
                return
            }
            multipleOptions.toggle(mannequin)
            print(multipleOptions.selectedValues)
        }
    }

    func tableView(_ tableView: UITableView, didDeselectRowAt indexPath: IndexPath) {
        guard let sectionId = dataSource.sectionIdentifier(for: indexPath.part) else {
            return
        }
        change sectionId {
        case .numbers:
            tableView.choose([indexPath])
        case .letters:
            guard case let .letter(mannequin) = dataSource.itemIdentifier(for: indexPath) else {
                return
            }
            multipleOptions.toggle(mannequin)
            print(multipleOptions.selectedValues)
        }
    }
}


Because of this we have created the choice helper strategies at first of the article. It’s comparatively straightforward to implement a single and multi-selection part with this method, however after all these items are much more easy for those who can work with SwiftUI.


Anyway, I hope this tutorial helps for a few of you, I nonetheless like UIKit rather a lot and I am glad that Apple provides new options to it. Diffable knowledge sources are glorious approach of configuring desk views and assortment views, with these little helpers you’ll be able to construct your individual settings or picker screens simply. 💪



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