Drill down picker for Caseiterable & RawRepresentable collections

picker.swift

//  Created by Andrew Cowley on 01/12/2021.
//
import SwiftUI

enum Priority: String, Pickable {
   case none, low, medium, high           // any raw type can be used
}

struct ContentView: View {
   @State var priority: Priority = .none
   let link = Image(systemName: "chevron.right")
   var body: some View {
      NavigationView {
         Form {
            Section {
               // Custom picker:
            	InsetPicker("Priority", selection: $priority)

               // Compare with Apple picker code:
               Picker("Priority", selection: $priority) {
                  ForEach(Priority.allCases) { p in
                     Text(p.description).tag(p)
                  }
               }
            }
         } .navigationTitle("Details")
      }
   }
}
/// Drill down picker with a grouped list style
struct InsetPicker<T: Pickable>: View where T.AllCases: RandomAccessCollection {
   /* Argument */
   @Binding var selectedValue: T
   let title: String
   /* Configuration */
   @State private var showPicker = false

   var body: some View {
      formText
      	// Add .padding to create space for the chevron overlayed by navlink
         .padding(.trailing, 20)
         .overlay {
            NavigationLink("", isActive: $showPicker ) {
               listPicker
            }
         }
   }

   /// The row on the calling view that will be clicked to trigger the picker
   var formText: some View {
      HStack {
         Text("\(title)")
         Spacer()
         Text("\(selectedValue.description)")
            .foregroundColor(Color.secondary)
      }
   }

   /// Picker styled on an insetGrouped List
   var listPicker: some View {
      List {
         ForEach(T.allCases) { t in
            HStack {
               Text(t.description)
               Spacer()
               checkmark(for: t)
            }
            // Overlay an invisible button across each row
            .overlay(selectionButton(t: t))
         }
      }
      .listStyle(.insetGrouped)
      .toolbar {
         ToolbarItem(placement: .principal) {
            Text(title)
         }
      }
   }

   func selectionButton(t: T) -> some View {
      Button(" ") {
         // Replicate slightly annoying feature where the current row cannot
         // be selected to dismiss the picker
         guard selectedValue != t else { return }
         selectedValue = t
         showPicker = false
      }
   }
	/// Return a checkmark if the supplied value matches the selectedValue
   func checkmark(for t: T) -> some View {
      Group {
         if t == selectedValue {
            Text(Image(systemName: "checkmark"))
               .foregroundColor(Color.accentColor)
               .bold()
         } else {
            EmptyView()
         }
      }
   }

   init(_ title: String, selection v: Binding<T>) {
      self.title = title
      self._selectedValue = v
      self.showPicker = true
   }
}

protocol Pickable: Identifiable, Equatable, CaseIterable, RawRepresentable {
   var description: String {get}
}

extension Pickable {
   var id: String { "\(self.rawValue)" }
   var description: String { "\(self.rawValue)".capitalized }
}