【SwiftUI】@State を 子 View でどう受けるか 🤔 - @binding 👉 https://android.benigumo.com/20231224/state-binding/

State-Binding.swift

import SwiftUI
import PlaygroundSupport

struct ParentView: View {
  @State private var text: String = ""

  var body: some View {
    VStack {
      TextField("Parent", text: $text)
      Text(text)
      Divider()

      ChildView(text: $text)

    }
    .padding()
  }
}

//struct ChildView: View {
//  private var text: Binding<String>
//
//  init(text: Binding<String>) {
//    self.text = text
//  }
//
//  var body: some View {
//    TextField("Child", text: text)
//    Text(text.wrappedValue)
//  }
//}

//struct ChildView: View {
//  var text: Binding<String>
//
//  var body: some View {
//    TextField("Child", text: text)
//    Text(text.wrappedValue)
//  }
//}

// NG
//struct ChildView: View {
//  @Binding private var text: String
//
//  init(text: Binding<String>) {
//    self.text.projectedValue = text  // NG
//  }
//
//  var body: some View {
//    TextField("Child", text: $text)
//    Text(text)
//  }
//}

// NG
//struct ChildView: View {
//  @State private var text: String
//
//  init(text: Binding<String>) {
//    self.text = text.wrappedValue
//  }
//
//  var body: some View {
//    TextField("Child", text: $text)
//    Text(text)
//  }
//}

// 主流?
//struct ChildView: View {
//  @Binding private var text: String
//
//  init(text: Binding<String>) {
//    _text = text
//  }
//
//  var body: some View {
//    TextField("Child", text: $text)
//    Text(text)
//  }
//}

struct ChildView: View {
  @Binding var text: String

  var body: some View {
    TextField("Child", text: $text)
    Text(text)
  }
}

PlaygroundPage.current.setLiveView(
  ParentView()
    .frame(width: 300, height: 300)
)