How to improve SwiftUI Picker performance on macOS

Question

In an ongoing exercise of migrating a small form app from AppKit to SwiftUI I have encountered a significant performance difference between AppKit PopUpButton and SwiftUI Picker. It is a Picker with a longish list (433 items - ISO639 language list). Under AppKit the PopUpButton opens instantly for all intents and purposes. Under SwiftUI the picker is taking 4-5 seconds from click to list being presented. Sufficiently long for the spinning beachball to appear.

I am guessing that it is dynamically creating the subview of items after the mouse click. Has anyone experience with long picker lists and encountered performance issues? I did an experiment with unrolling the ForEach loop that the picker is built from into a view with Groups within Groups within Groups (that did work) ....however, it took fractionally longer.

The PickerView is:

struct ISO639Picker: View {
  @Binding var selection: ISO639LanguageCode
  var body: some View {
    Picker("", selection: $selection) {
      ForEach(codeSet.codes) { code in
        Text(code.alpha3B).tag(code)
      }
    }
  }
}

For completeness, codeSet is a global instance of Class that populates from an ISO639 text source and it is instantiated at app startup. The "codes" member is an array of structures as below.

public struct ISO639LanguageCode: Hashable,Identifiable {
  public var id = UUID()
  public var alpha3B: String
  public var alpha3T: String
  public var alpha2: String
  public var name: String
  public var family: String
}

Any suggestions on where the performance issue may be would be appreciated.

Answer 1

I have found coercing a Menu to behave like a Picker to be more performant.

Menu {
    ForEach(codeSet.codes) { code in
        Button("\(code.alpha3B)", action: { self.selection = code })
    }
} label: {
    Text("\(self.selection.alpha3B)")
}

Answer 2

For anyone encountering the same issue, the resolution, for me, is to use Adams' suggestion of an NSPopupButton wrapped in an NSViewRepresentable. It took a while to determine the right notification to hook up with. An implementation that is sufficient for my needs is offered below;

struct NSPopUpButtonView<ItemType>: NSViewRepresentable where ItemType:Equatable {
  @Binding var selection: ItemType
  var popupCreator: () -> NSPopUpButton
  
  typealias NSViewType = NSPopUpButton
  
  func makeNSView(context: NSViewRepresentableContext<NSPopUpButtonView>) -> NSPopUpButton {
    let newPopupButton = popupCreator()
    setPopUpFromSelection(newPopupButton, selection: selection)
    return newPopupButton
  }
  
  func updateNSView(_ nsView: NSPopUpButton, context: NSViewRepresentableContext<NSPopUpButtonView>) {
    setPopUpFromSelection(nsView, selection: selection)
  }
  
  func setPopUpFromSelection(_ button:NSPopUpButton, selection:ItemType)
  {
    let itemsList = button.itemArray
    let matchedMenuItem = itemsList.filter{($0.representedObject as! ItemType) == selection}.first
    if matchedMenuItem != nil
    {
      button.select(matchedMenuItem)
    }
  }
  
  func makeCoordinator() -> Coordinator {
    return Coordinator(self)
  }
  
  class Coordinator:NSObject {
    var parent: NSPopUpButtonView!
    
    init(_ parent: NSPopUpButtonView)
    {
      super.init()
      self.parent = parent
      NotificationCenter.default.addObserver(self,
                                             selector: #selector(dropdownItemSelected),
                                             name: NSMenu.didSendActionNotification,
                                             object: nil)
    }
    
    @objc func dropdownItemSelected(_ notification: NSNotification)
    {
      let menuItem = (notification.userInfo?["MenuItem"])! as! NSMenuItem
      parent.selection = menuItem.representedObject as! ItemType
    }
  }
}