SwiftUI View with a HostingView helper.

CustomIconView.swift

import SwiftUI

// MARK: - CustomIconView

struct CustomIconView: View {
  let containerSize: CGSize
  let imageSize: CGSize
  let nsImage: NSImage?

  @Environment(\.colorScheme) var colorScheme

  var isDarkMode: Bool {
    colorScheme == .dark
  }

  var body: some View {
    Group {
      if let nsImage = nsImage {
        DeadCenterView {
          Image(nsImage: nsImage)
            .resizable()
            .frame(width: imageSize.width, height: imageSize.height)
            .scaledToFit()
            .shadow(
              color: Color.black.opacity(0.15),
              radius: 0,
              x: 0,
              y: 0
            )
        }
      }
    }
    .frame(width: containerSize.width, height: containerSize.height)
    .background(
      ZStack {
        Rectangle().fill(.ultraThinMaterial)
        RadialGradient(
          gradient: Gradient(
            colors: [
              Color.white,
              Color.white.opacity(1),
              Color.white.opacity(0.9),
              Color.white.opacity(0.1),
              Color.white.opacity(0.0),
            ]
          ),
          center: .center,
          startRadius: 0,
          endRadius: 30
        )
        .blendMode(.lighten)
      }
    )
    .brandBorder(
      Color.white.opacity(isDarkMode ? 0.05 : 0.15),
      cornerRadius: 8
    )
    .shadow(
      color: Color.black.opacity(0.05),
      radius: 4,
      x: 0,
      y: 0
    )
  }
}

// MARK: - SomeHostedView

class SomeHostedView<ContentView: View>: NSView {
  private(set) var hostingView: NSHostingView<ContentView>?

  // MARK: Lifecycle

  init(content: ContentView, frame: CGRect) {
    super.init(frame: frame)

    let rootView = NSHostingView(rootView: content)

    if let hostingView = hostingView {
      hostingView.rootView = content
    } else {
      let hostingView = rootView

      addSubview(hostingView)

      hostingView.translatesAutoresizingMaskIntoConstraints = false
      NSLayoutConstraint.activate([
        hostingView.leadingAnchor.constraint(equalTo: leadingAnchor),
        hostingView.trailingAnchor.constraint(equalTo: trailingAnchor),
        hostingView.topAnchor.constraint(greaterThanOrEqualTo: topAnchor),
        hostingView.centerYAnchor.constraint(equalTo: centerYAnchor),
        hostingView.bottomAnchor.constraint(lessThanOrEqualTo: bottomAnchor),
      ])

      self.hostingView = hostingView
    }
  }

  required init?(coder _: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }
}

// MARK: - HostedFavicon

struct HostedFavicon: NSViewRepresentable {
  let view = SomeHostedView(
    content: CustomIconView(
      containerSize: AppSegmentGroupItemDrawingView.AppIconSize,
      imageSize: AppSegmentGroupItemDrawingView.FaviconSize,
      nsImage: NSImage(named: "quick-start-dan-circle")
    ),
    frame: CGRect(
      x: 0,
      y: 0,
      width: AppSegmentGroupItemDrawingView.AppIconSize.width,
      height: AppSegmentGroupItemDrawingView.AppIconSize.height
    )
  )
  func makeNSView(context _: Context) -> some SomeHostedView<CustomIconView> { view }
  func updateNSView(_: NSViewType, context _: Context) { }
}

// MARK: - HostedFavicon_Previews

struct HostedFavicon_Previews: PreviewProvider {
  static var previews: some View {
    HostedFavicon()
      .frame(width: 50, height: 50)
  }
}