An approach for simplified wrapping of AppKit and UIKit views in SwiftUI

SwiftUI WrapView handler approach.swift

import SwiftUI

#if os(macOS)
typealias OSView = NSView
typealias OSViewRepresentable = NSViewRepresentable

#elseif os(iOS)
typealias OSView = UIView
typealias OSViewRepresentable = UIViewRepresentable
#endif

/// Example usage:
/// ```
/// WrapView(handlers: .handlers(
///     makeView: { (context) -> NSTextField in
///         let view = NSTextField()
///         view.delegate = context.coordinator
///         return view
///     },
///     updateView: { (view, context) in
///         // ...
///     }
/// )
/// ```
struct WrapView<ViewType: OSView>: OSViewRepresentable {
    typealias MakeView = (Context) -> ViewType
    typealias UpdateView = (ViewType, Context) -> Void
    
    let handlers: Handlers
    
    init(handlers: Handlers) {
        self.handlers = handlers
    }
    
    struct Handlers {
        let makeView: MakeView
        let updateView: UpdateView?
        static func handlers(makeView: @escaping MakeView, updateView: UpdateView? = nil) -> Handlers {
            return Handlers(makeView: makeView, updateView: updateView)
        }
    }
    
    #if os(macOS)
    func makeNSView(context: Context) -> ViewType { self.handlers.makeView(context) }
    func updateNSView(_ view: ViewType, context: Context) { self.handlers.updateView?(view, context) }

    #elseif os(iOS)
    func makeUIView(context: Context) -> ViewType { self.handlers.makeView(context) }
    func updateUIView(_ view: ViewType, context: Context) { self.handlers.updateView?(view, context) }
    #endif
}

/// Example usage:
/// ```
/// WrapViewWithCoordinator(handlers: .handlers(
///     makeView: { (context) -> NSTextField in
///         let view = NSTextField()
///         view.delegate = context.coordinator
///         return view
///     },
///     updateView: { (view, context) in
///         // ...
///     },
///     makeCoordinator: {
///         Coordinator()
///     })
/// )
/// ```
struct WrapViewWithCoordinator<ViewType: OSView, Coordinator>: OSViewRepresentable {
    typealias MakeView = (_ context: Context) -> ViewType
    typealias UpdateView = (_ View: ViewType, _ context: Context) -> Void
    typealias MakeCoordinator = () -> Coordinator

    let handlers: Handlers
    
    init(handlers: Handlers) {
        self.handlers = handlers
    }
    
    struct Handlers {
        let makeView: MakeView
        let updateView: UpdateView
        let makeCoordinator: MakeCoordinator
        static func handlers(makeView: @escaping MakeView, updateView: @escaping UpdateView, makeCoordinator: @escaping MakeCoordinator) -> Handlers {
            return Handlers(makeView: makeView, updateView: updateView, makeCoordinator: makeCoordinator)
        }
    }
    
    #if os(macOS)
    func makeNSView(context: Context) -> ViewType { self.handlers.makeView(context) }
    func updateNSView(_ view: ViewType, context: Context) { self.handlers.updateView(view, context) }
    func makeCoordinator() -> Coordinator { self.handlers.makeCoordinator() }

    #elseif os(iOS)
    func makeUIView(context: Context) -> ViewType { self.handlers.makeView(context) }
    func updateUIView(_ view: ViewType, context: Context) { self.handlers.updateView(view, context) }
    func makeCoordinator() -> Coordinator { self.handlers.makeCoordinator() }
    #endif
}