SwiftUI 中的 @AppStorage — 它是什么、UserDefaults 和存储设置

enum AppTheme: String {
    case system, light, dark
}

struct SettingsView: View {
    @AppStorage("username") var username: String = "Guest"
    @AppStorage("launchCount") var launchCount: Int = 0
    @AppStorage("isDarkMode") var isDarkMode: Bool = false
    @AppStorage("appTheme") var theme: AppTheme = .system
    @AppStorage("lastOpened") var lastOpened: Date? = nil

    var body: some View {
        Form {
            TextField("Username", text: $username)
            Toggle("Dark mode", isOn: $isDarkMode)
            Text("已启动 \(launchCount) 次")
        }
    }
}

struct ThemeSettingView: View {
    @AppStorage("isDarkMode") var isDarkMode: Bool = false

    var body: some View {
        VStack {
            Toggle("Dark Mode", isOn: $isDarkMode)
                .onChange(of: isDarkMode) { oldValue, newValue in
                    print("深色模式已更改为 \(newValue)")
                }
        }
    }
}

struct AppSettingsView: View {
    @AppStorage("displayName") var displayName = ""
    @AppStorage("notificationsEnabled") var notificationsEnabled = true
    @AppStorage("maxResults") var maxResults = 25
    @AppStorage("selectedTab") var selectedTab = "home"

    var body: some View {
        NavigationStack {
            Form {
                Section(header: Text("个人资料")) {
                    TextField("Display name", text: $displayName)
                }

                Section(header: Text("偏好设置")) {
                    Toggle("Enable notifications",
                           isOn: $notificationsEnabled)
                    Stepper("Max results: \(maxResults)",
                           value: $maxResults,
                           in: 10...100,
                           step: 5)
                }

                Section {
                    Button("重置设置") {
                        UserDefaults.standard.removePersistentDomain(
                            forName: Bundle.main.bundleIdentifier!)
                    }
                    .tint(.red)
                }
            }
            .navigationTitle("Settings")
        }
    }
}

struct SharedSettingsView: View {
    let sharedDefaults = UserDefaults(suiteName: "group.com.example.app")

    @AppStorage("widgetTheme", store: UserDefaults(suiteName: "group.com.example.app")!)
    var widgetTheme: String = "系统"

    @AppStorage("widgetColor", store: UserDefaults(suiteName: "group.com.example.app")!)
    var widgetColor: String = "蓝色"

    var body: some View {
        Form {
            Picker("Widget theme", selection: $widgetTheme) {
                Text("系统").tag("system")
                Text("浅色").tag("浅色")
                Text("深色").tag("深色")
            }
            Picker("Accent color", selection: $widgetColor) {
                Text("蓝色").tag("blue")
                Text("绿色").tag("绿色")
                Text("红色").tag("红色")
            }
        }
    }
}