Component Templates

TemplateView.swift

import Foundation
import UIKit

import RxSwift
import SnapKit

final class TemplateView: UIView, StatefulComponent {
    var state: State? {
        didSet { stateDidChange(from: oldValue) }
    }

    var handlers = Handlers() {
        didSet { handlersDidChange() }
    }

    var bindBag = DisposeBag()

//    private var subview: Subview!
//    private var component: Component!

    private var pendingLayoutChange: (from: Layout?, to: Layout?)?

    init() {
        super.init(frame: .zero)
        setupSubviews()
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError()
    }

    private func setupSubviews() {
        // ...setup self...
        // layoutMargins =

        // subview = Subview()
        // ...setup subview...
        // addSubview(subview)

        // component = components.makeComponent()
        // ...setup component...
        // addSubview(component.view)
    }

    private func stateDidChange(from oldState: State?) {
        guard state != oldState else { return }

        // ...set substates...

        layoutDidChange(from: oldState?.layout)
        appearanceDidChange(from: oldState?.appearance)
    }

    private func layoutDidChange(from oldLayout: Layout?) {
        guard state?.layout != oldLayout else { return }
        pendingLayoutChange = (from: oldLayout, to: state?.layout)
        setNeedsUpdateConstraints()
    }

    private func appearanceDidChange(from oldAppearance: Appearance?) {
        guard state?.appearance != oldAppearance else { return }
        guard let appearance = state?.appearance else { /* handle nil if needed */ return }

        // applying { ... }
        // subview.applying { ... }
    }

    private func handlersDidChange() {}

    public override func updateConstraints() {
        defer {
            pendingLayoutChange = nil
            super.updateConstraints()
        }
        guard let pendingLayoutChange = pendingLayoutChange else { return }
        guard let _ = pendingLayoutChange.to else { /* handle nil if needed */ return }

        // ...remake (update) snapkit constraints...
    }
}

extension TemplateView {
    struct State: Equatable {
        // var title: String
        // var subcomponent: Subcomponent.State
        var layout = Layout()
        var appearance: Appearance
    }

    struct Layout: Equatable {
        // ...props...
    }

    struct Appearance: Equatable {
        // var backgroundColor: UIColor
    }

    struct Handlers {
        // var onSmth: ...some closure...
    }
}