[SwiftUI macOS アプリ] NavigationView List の Detail 画面で TextField を使うサンプル（Optional Binding）

ポイントはオプショナルをバインディングするところです。extension を追加しています。

ContentView.swift

import SwiftUI

struct Person: Identifiable, Hashable {
    var name: String
    var id = UUID()
    var order: Int
}

struct ContentView: View {
    
    @State var persons = [
        Person(name: "taro", order: 2),
        Person(name: "yuki", order: 1),
        Person(name: "hoge", order: 0)
    ]
    
    @State private var selectedPerson: Person?
    
    var body: some View {
        VStack {
            HStack {
                AddButton(persons: $persons, selected: $selectedPerson)
                Button("remove", action: {
                    print(self.selectedPerson)
                    if self.selectedPerson == nil {
                        return
                    }
                    self.persons.removeAll(where: {$0.id == self.selectedPerson!.id})
                    self.selectedPerson = nil
                })
            }
            NavigationView {
                List(persons.sorted{$0.order > $1.order}, id: \.self, selection: $selectedPerson) { person in
                    Text(person.name)
                }.frame(width: 150)

                if selectedPerson != nil {
                    Detail(person: $selectedPerson.bound)
                } else {
                    Text("nothing").frame(maxWidth: .infinity, maxHeight: .infinity)
                }
            }.frame(maxWidth: .infinity, maxHeight: .infinity)
        }
    }
}

struct AddButton: View {
    @Binding var persons: [Person]
    @Binding var selected: Person?
    var body: some View {
        Button("add", action: {
            let names = ["foo", "bar", "baz", "tao", "tee"]
            let newPerson = Person(name: names.randomElement()!, order: self.persons.count)
            self.persons.append(newPerson)
            self.selected = newPerson
        })
    }
}

extension Optional where Wrapped == Person {
    var _bound: Person? {
        get { return self }
        set { self = newValue }
    }
    
    var bound: Person {
        get { return _bound ?? Person(name: "", order: 9999) }
        set { _bound = newValue }
    }
}

struct Detail: View {
    @Binding var person: Person
    var body: some View {
        VStack {
            TextField("", text: $person.name)
            Text(person.name)
        }.frame(maxWidth: .infinity, maxHeight: .infinity)
    }
}

参考