Persistence

UserDefaults API

Store small preferences like flags or last-used values.

Syntax:

• UserDefaults.standard.set(_:forKey:)
• .bool(forKey:)
• SwiftUI @AppStorage("key")

Example

Demo.swift

ContentView.swift

App.swift

import SwiftUI

struct UserDefaultsDemo: View {
  @AppStorage("username") private var username = ""
  var body: some View {
VStack(spacing: 12) {
  Text(username.isEmpty ? "Hello, Guest" : "Hello, " + username)
  TextField("Username", text: $username)
    .textFieldStyle(.roundedBorder)
}
.padding()
  }
}

The UserDefaults API provides a simple way to store small preferences and settings, such as flags or last-used values.

Tip: For larger data or sync, use Core Data or CloudKit.

Avoid storing secrets in UserDefaults.

App Group Shared Defaults (Widget Access)

Share small values between your app and a Widget (or extensions) using an App Group suite.

Syntax:

• UserDefaults(suiteName: "group.id")
• shared.set(_:forKey:)
• shared.integer(forKey:)

Example

Demo.swift

ContentView.swift

App.swift

import SwiftUI
import Foundation

struct AppGroupDemo: View {
  private let suite = UserDefaults(suiteName: "group.com.example.notes")!
  @State private var count: Int = 0
  var body: some View {
VStack(spacing: 12) {
  Text("Notes count: \(count)")
  HStack {
    Button("Increment") { count += 1; suite.set(count, forKey: "notesCount") }
    Button("Load") { count = suite.integer(forKey: "notesCount") }
    Button("Clear") { suite.removeObject(forKey: "notesCount"); count = 0 }
  }
}
.task { count = suite.integer(forKey: "notesCount") }
.padding()
  }
}