@Binding for child communication in iOS Swift

Introduction

@Binding lets a child view read and write a value owned by its parent. This helps keep data in sync between views.

When a parent view owns some data but a child view needs to update it.

When you want to share state between views without duplicating it.

When building forms where child inputs change parent data.

When you want a child view to control a toggle or slider that affects parent state.

Syntax

iOS Swift

struct ChildView: View {
  @Binding var isOn: Bool

  var body: some View {
    Toggle("Switch", isOn: $isOn)
  }
}

Use @Binding in the child to declare a variable that links to the parent's state.

Pass the binding from the parent using the $ prefix.

Examples

The parent owns the isOn state and passes a binding to the child.

iOS Swift

struct ParentView: View {
  @State private var isOn = false

  var body: some View {
    ChildView(isOn: $isOn)
  }
}

The child can modify the parent's count state through the binding.

iOS Swift

struct ChildView: View {
  @Binding var count: Int

  var body: some View {
    Button("Increment") {
      count += 1
    }
  }
}

Sample App

This app shows a toggle switch controlled by the child view. The parent displays the current state text. Changing the toggle updates the parent's state instantly.

iOS Swift

import SwiftUI

struct ParentView: View {
  @State private var isOn = false

  var body: some View {
    VStack {
      Text(isOn ? "Switch is ON" : "Switch is OFF")
        .font(.title)
        .padding()
      ChildView(isOn: $isOn)
        .padding()
    }
  }
}

struct ChildView: View {
  @Binding var isOn: Bool

  var body: some View {
    Toggle("Toggle Switch", isOn: $isOn)
      .padding()
  }
}

struct ContentView: View {
  var body: some View {
    ParentView()
  }
}

Important Notes

Always prefix the parent's state with $ when passing to a @Binding variable.

Bindings keep data in sync both ways: child changes update parent and parent changes update child.

Use @State in the parent and @Binding in the child for this pattern.

Summary

@Binding lets child views read and write parent state.

Pass bindings from parent to child using $ prefix.

This keeps data synchronized between views easily.