Agent skill

swiftui-patterns

SwiftUI 架构模式,使用 @Observable 进行状态管理,视图组合,导航,性能优化,以及现代 iOS/macOS UI 最佳实践。

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SKILL.md

SwiftUI 模式

适用于 Apple 平台的现代 SwiftUI 模式,用于构建声明式、高性能的用户界面。涵盖 Observation 框架、视图组合、类型安全导航和性能优化。

何时激活

  • 构建 SwiftUI 视图和管理状态时(@State@Observable@Binding
  • 使用 NavigationStack 设计导航流程时
  • 构建视图模型和数据流时
  • 优化列表和复杂布局的渲染性能时
  • 在 SwiftUI 中使用环境值和依赖注入时

状态管理

属性包装器选择

选择最适合的最简单包装器:

包装器 使用场景
@State 视图本地的值类型(开关、表单字段、Sheet 展示)
@Binding 指向父视图 @State 的双向引用
@Observable 类 + @State 拥有多个属性的自有模型
@Observable 类(无包装器) 从父视图传递的只读引用
@Bindable 指向 @Observable 属性的双向绑定
@Environment 通过 .environment() 注入的共享依赖项

@Observable ViewModel

使用 @Observable(而非 ObservableObject)—— 它跟踪属性级别的变更,因此 SwiftUI 只会重新渲染读取了已变更属性的视图:

swift
@Observable
final class ItemListViewModel {
    private(set) var items: [Item] = []
    private(set) var isLoading = false
    var searchText = ""

    private let repository: any ItemRepository

    init(repository: any ItemRepository = DefaultItemRepository()) {
        self.repository = repository
    }

    func load() async {
        isLoading = true
        defer { isLoading = false }
        items = (try? await repository.fetchAll()) ?? []
    }
}

消费 ViewModel 的视图

swift
struct ItemListView: View {
    @State private var viewModel: ItemListViewModel

    init(viewModel: ItemListViewModel = ItemListViewModel()) {
        _viewModel = State(initialValue: viewModel)
    }

    var body: some View {
        List(viewModel.items) { item in
            ItemRow(item: item)
        }
        .searchable(text: $viewModel.searchText)
        .overlay { if viewModel.isLoading { ProgressView() } }
        .task { await viewModel.load() }
    }
}

环境注入

@Environment 替换 @EnvironmentObject

swift
// Inject
ContentView()
    .environment(authManager)

// Consume
struct ProfileView: View {
    @Environment(AuthManager.self) private var auth

    var body: some View {
        Text(auth.currentUser?.name ?? "Guest")
    }
}

视图组合

提取子视图以限制失效

将视图拆分为小型、专注的结构体。当状态变更时,只有读取该状态的子视图会重新渲染:

swift
struct OrderView: View {
    @State private var viewModel = OrderViewModel()

    var body: some View {
        VStack {
            OrderHeader(title: viewModel.title)
            OrderItemList(items: viewModel.items)
            OrderTotal(total: viewModel.total)
        }
    }
}

用于可复用样式的 ViewModifier

swift
struct CardModifier: ViewModifier {
    func body(content: Content) -> some View {
        content
            .padding()
            .background(.regularMaterial)
            .clipShape(RoundedRectangle(cornerRadius: 12))
    }
}

extension View {
    func cardStyle() -> some View {
        modifier(CardModifier())
    }
}

导航

类型安全的 NavigationStack

使用 NavigationStackNavigationPath 来实现程序化、类型安全的路由:

swift
@Observable
final class Router {
    var path = NavigationPath()

    func navigate(to destination: Destination) {
        path.append(destination)
    }

    func popToRoot() {
        path = NavigationPath()
    }
}

enum Destination: Hashable {
    case detail(Item.ID)
    case settings
    case profile(User.ID)
}

struct RootView: View {
    @State private var router = Router()

    var body: some View {
        NavigationStack(path: $router.path) {
            HomeView()
                .navigationDestination(for: Destination.self) { dest in
                    switch dest {
                    case .detail(let id): ItemDetailView(itemID: id)
                    case .settings: SettingsView()
                    case .profile(let id): ProfileView(userID: id)
                    }
                }
        }
        .environment(router)
    }
}

性能

为大型集合使用惰性容器

LazyVStackLazyHStack 仅在视图可见时才创建它们:

swift
ScrollView {
    LazyVStack(spacing: 8) {
        ForEach(items) { item in
            ItemRow(item: item)
        }
    }
}

稳定的标识符

ForEach 中始终使用稳定、唯一的 ID —— 避免使用数组索引:

swift
// Use Identifiable conformance or explicit id
ForEach(items, id: \.stableID) { item in
    ItemRow(item: item)
}

避免在 body 中进行昂贵操作

  • 切勿在 body 内执行 I/O、网络调用或繁重计算
  • 使用 .task {} 处理异步工作 —— 当视图消失时它会自动取消
  • 在滚动视图中谨慎使用 .sensoryFeedback().geometryGroup()
  • 在列表中最小化使用 .shadow().blur().mask() —— 它们会触发屏幕外渲染

遵循 Equatable

对于 body 计算昂贵的视图,遵循 Equatable 以跳过不必要的重新渲染:

swift
struct ExpensiveChartView: View, Equatable {
    let dataPoints: [DataPoint] // DataPoint must conform to Equatable

    static func == (lhs: Self, rhs: Self) -> Bool {
        lhs.dataPoints == rhs.dataPoints
    }

    var body: some View {
        // Complex chart rendering
    }
}

预览

使用 #Preview 宏配合内联模拟数据以进行快速迭代:

swift
#Preview("Empty state") {
    ItemListView(viewModel: ItemListViewModel(repository: EmptyMockRepository()))
}

#Preview("Loaded") {
    ItemListView(viewModel: ItemListViewModel(repository: PopulatedMockRepository()))
}

应避免的反模式

  • 在新代码中使用 ObservableObject / @Published / @StateObject / @EnvironmentObject —— 迁移到 @Observable
  • 将异步工作直接放在 bodyinit 中 —— 使用 .task {} 或显式的加载方法
  • 在不拥有数据的子视图中将视图模型创建为 @State —— 改为从父视图传递
  • 使用 AnyView 类型擦除 —— 对于条件视图,优先选择 @ViewBuilderGroup
  • 在向 Actor 传递数据或从 Actor 接收数据时忽略 Sendable 要求

参考

查看技能:swift-actor-persistence 以了解基于 Actor 的持久化模式。 查看技能:swift-protocol-di-testing 以了解基于协议的 DI 和使用 Swift Testing 进行测试。

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