master-detail-example

//  Created by Marvin Lee Kobert on 29.07.23.
//  
//

import SwiftUI

// MARK: Item Model
struct Item: Identifiable, Hashable {
  let id: UUID
  let title: String
  let subitems: [Item]

  init(id: UUID = .init(), title: String, subitems: [Item] = []) {
    self.id = id
    self.title = title
    self.subitems = subitems
  }
}

// MARK: ViewModel
final class ViewModel: ObservableObject {
  @Published var items: [Item]

  init() {
    self.items = Self.sampleItems()
  }

  func persist(item: Item, withID id: UUID) {
    guard let index = items.firstIndex(where: { $0.id == id }) else {
      print("Cannot find item")
      return
    }

    items[index] = item
  }

  private static func sampleItems() -> [Item] {
    let subItems: [Item] = [.init(title: "First Subitem"), .init(title: "Second Subitem")]

    return [.init(title: "First Item", subitems: subItems)]
  }
}

// MARK: Master View
struct MasterView: View {
  @StateObject private var viewModel = ViewModel()

  var body: some View {
    NavigationStack {
      List {
        // You need to identify the item over the hashValue, so the list will redraw if the title or subitems change,
        // because the id is fixed.
        ForEach(viewModel.items, id: \.hashValue) { item in
          NavigationLink(item.title) {
            DetailView(item: item)
          }
        }
      }
      .navigationTitle("Items")
    }
    .environmentObject(viewModel)
  }
}

struct DetailView: View {
  @EnvironmentObject private var viewModel: ViewModel
  @Environment(\.dismiss) private var dismiss

  let item: Item

  @State private var title: String

  init(item: Item) {
    self.item = item
    self._title = .init(initialValue: item.title)
  }

  var body: some View {
    Form {
      Section {
        Text("Trying to change the text in the title textfield **in the middle of the text** unexpectedly moves the cursor to the end of the text.")
          .font(.caption)
          .padding()
      }

      Section("Title Textfield") {
        TextField("", text: $title)
      }

      Section("Subitems") {
        ForEach(item.subitems) { subitem in
          NavigationLink {
            DetailView(item: subitem)
          } label: {
            Text(subitem.title)
          }
        }
      }

      Section {
        Button("Save") {
          // Generate a new Item with the ID and subitems from the old item, with the new title
          let newItem: Item = .init(id: item.id, title: title, subitems: item.subitems)
          viewModel.persist(item: newItem, withID: item.id)
          dismiss()
        }
      }
    }
  }
}

struct MasterView_Previews: PreviewProvider {
  static var previews: some View {
    MasterView()
  }
}