UIWrapping, Wrapping UIKit to SwiftUI

UIWrapping.swift

import SwiftUI

/// Provides a convenient 'wrapper' around a UIView
public struct UIWrapping<V>: View {
    let wrapped: AnyView
    public var body: some View { wrapped }

    // MARK: Initializers

    /// Instantiates a wrapper for a `UIView`
    /// - Parameters:
    ///   - viewProvider: Use this closure to return an instantiated `UIView`
    ///   - updateHandler: Use this closure to configure the view, this is called for all SwiftUI view updates as well
    public init(_ provider: @escaping RepresentableProvider<V>, update handler: RepresentableUpdater<V>? = nil) where V: UIView {
        self.wrapped = AnyView(
            ViewWrapper(
                provider: provider,
                updater: handler
            )
        )
    }

    /// Instantiates a wrapper for a `UIView` – uses `.init(frame:)`
    /// - Parameters:
    ///   - type: The type of `UIView` to wrap
    ///   - updateHandler: Use this closure to configure the view, this is called for all SwiftUI view updates as well
    public init(_ type: V.Type = V.self, update handler: @escaping (V) -> Void) where V: UIView {
        self.wrapped = AnyView(
            ViewWrapper(
                provider: { V(frame: .zero) },
                updater: handler
            )
        )
    }

    /// Instantiates a wrapper for the specified viewProvider
    /// - Parameters:
    ///   - viewProvider: Use this closure to return an instantiated `UIView`
    ///   - updateHandler: Use this closure to configure the view, this is called for all SwiftUI view updates as well
    public init(_ provider: @escaping RepresentableProvider<V>, update handler: RepresentableUpdater<V>? = nil) where V: UIViewController {
        self.wrapped = AnyView(
            ViewControllerWrapper(
                provider: provider,
                updater: handler
            )
        )
    }

    /// Instantiates a wrapper for a `UIViewController` – uses `.init(nibName:bundle:)`
    /// - Parameters:
    ///   - type: The type of `UIViewController` to wrap
    ///   - handler: Use this closure to configure the view, this is called for all SwiftUI view updates as well
    public init(_ type: V.Type = V.self, update handler: @escaping (V) -> Void) where V: UIViewController {
        self.wrapped = AnyView(
            ViewControllerWrapper(
                provider: { V(nibName: nil, bundle: nil) },
                updater: handler
            )
        )
    }
}

// MARK: - Private ViewWrapper

public typealias RepresentableProvider<V> = () -> V
public typealias RepresentableUpdater<V> = (V) -> Void

private struct ViewWrapper<V: UIView>: UIViewRepresentable {
    let provider: RepresentableProvider<V>
    let updater: RepresentableUpdater<V>?

    func makeUIView(context: Context) -> V {
        provider()
    }

    func updateUIView(_ view: V, context: Context) {
        view.backgroundColor = .clear
        updater?(view)
    }
}

// MARK: - Private ViewControllerWrapper

private struct ViewControllerWrapper<V: UIViewController>: UIViewControllerRepresentable {
    public typealias Provider = () -> V
    public typealias Updater = (V) -> Void

    let provider: Provider
    let updater: Updater?

    func makeUIViewController(context: Context) -> V {
        provider()
    }

    func updateUIViewController(_ controller: V, context: Context) {
        controller.view.backgroundColor = .clear
        updater?(controller)
    }
}

// MARK: - Previews

struct UIWrapping_Preview: PreviewProvider {
    static var previews: some View {
        VStack {
            UIWrapping<UILabel> { view in
                view.numberOfLines = 0
                view.text = "Hello 😄"
                view.textAlignment = .center
            }
            .fixedSize()

            UIWrapping<UIActivityIndicatorView> { view in
                view.startAnimating()
            }

            // Note: In case of UICollectionView must be initialized with a non-nil layout parameter.
            UIWrapping { () -> UICollectionView in
                let flowLayout = UICollectionViewFlowLayout()
                flowLayout.scrollDirection = .vertical
                flowLayout.minimumInteritemSpacing = 0
                flowLayout.minimumLineSpacing = 0
                flowLayout.sectionInset = .zero

                let collectionView = UICollectionView(frame: .zero, collectionViewLayout: flowLayout)
                collectionView.backgroundColor = .black
                collectionView.showsVerticalScrollIndicator = true
                return collectionView
            }
        }
    }
}