MVVM 与架构

SwiftUI 项目推荐 MVVM + Repository：View 薄、ViewModel 编排业务、Repository 抽象数据源。对照 /roadmaps/swift-ui「架构」节点，清晰分层便于测试与扩展。

学习目标

• 理解 MVVM 在 SwiftUI 中的职责划分
• 用 Protocol 定义 Repository，支持依赖注入
• 了解 Clean Architecture 分层思想
• 组织可维护的项目目录结构

核心概念

MVVM 分层

// Model
struct Track: Identifiable, Codable, Equatable {
    let id: Int
    var title: String
    var lessonCount: Int
}

// Repository 协议
protocol TrackRepositoryProtocol {
    func fetchAll() async throws -> [Track]
}

// 实现：可替换为网络 / 本地
final class TrackRepository: TrackRepositoryProtocol {
    func fetchAll() async throws -> [Track] {
        try await Task.sleep(nanoseconds: 300_000_000)
        return [
            Track(id: 1, title: "SwiftUI 入门", lessonCount: 12),
            Track(id: 2, title: "React 对照", lessonCount: 10),
        ]
    }
}

// ViewModel
@MainActor
final class TrackListViewModel: ObservableObject {
    @Published var tracks: [Track] = []
    @Published var isLoading = false
    @Published var errorMessage: String?

    private let repository: TrackRepositoryProtocol

    init(repository: TrackRepositoryProtocol = TrackRepository()) {
        self.repository = repository
    }

    func load() async {
        isLoading = true
        errorMessage = nil
        do {
            tracks = try await repository.fetchAll()
        } catch {
            errorMessage = error.localizedDescription
        }
        isLoading = false
    }
}

// View：只负责 UI
struct TrackListScreen: View {
    @StateObject private var viewModel = TrackListViewModel()

    var body: some View {
        Group {
            if viewModel.isLoading {
                ProgressView()
            } else {
                List(viewModel.tracks) { track in
                    Text("\(track.title)（\(track.lessonCount) 课）")
                }
            }
        }
        .task { await viewModel.load() }
        .alert("错误", isPresented: .constant(viewModel.errorMessage != nil)) {
            Button("确定") { viewModel.errorMessage = nil }
        } message: {
            Text(viewModel.errorMessage ?? "")
        }
    }
}

View 不含业务逻辑；ViewModel 通过 Protocol 注入 Repository，单元测试可传入 Mock。

项目结构

SwiftUIApp/
├── App/
│   └── SwiftUIAppApp.swift
├── Models/
│   └── Track.swift
├── ViewModels/
│   └── TrackListViewModel.swift
├── Views/
│   └── TrackListScreen.swift
├── Services/
│   └── TrackRepository.swift
└── Tests/
    └── TrackListViewModelTests.swift