【SwiftUI】@State と 単方向データフロー 👉 https://android.benigumo.com/20240407/binding-1/

TestDataFlow.swift

import SwiftUI

struct TestDataFlow: View {
  @State var text = ""
  @State var isOn = false

  var stateHolder = StateHolder()

  var body: some View {

    Text("\(text) \(isOn)").bold()

    // 1 双方向 @State + $
    TextField("text", text: $text)
    Toggle("toggle", isOn: $isOn)

    Divider()

    // 2 双方向 @State + Binding()
    TextField(
      "text",
      text: Binding(
        get: { text },
        set: { newValue in text = newValue }
      )
    )
    Toggle("toggle", isOn: Binding(
      get: { isOn },
      set: { newValue in isOn = newValue })
    )

    Divider()
    Divider()
    Divider()

    Text("\(stateHolder.text) \(stateHolder.isOn)").bold()

    // 3 単方向 @Obserevable + Binding()
    TextField("text", text: Binding(
      get: { stateHolder.text },
      set: { newValue in stateHolder.text = newValue })
    )
    Toggle("toggle", isOn: Binding(
      get: { stateHolder.isOn },
      set: { newValue in stateHolder.isOn = newValue })
    )

    Divider()

    // 4 単方向 @Observable + @Bindable
    @Bindable var sh = stateHolder
    TextField("text", text: $sh.text)
    Toggle("toggle", isOn: $sh.isOn)
  }
}

@Observable final class StateHolder {
  var text = ""
  var isOn = false
}

#Preview {
  TestDataFlow()
    .frame(width: 150)
}

【SwiftUI】ModelView は StateHolder なのか ? - ModelView の役割
👉 https://android.benigumo.com/20240407/binding-2/