综合练习：Todo App

用本 track 所学完成 Todo App：SwiftUI 界面 + MVVM + URLSession（或本地 Core Data）+ 单元测试。对照 /roadmaps/ios 全路径验收。

学习目标

• 完成可运行的 Todo 应用（增删改查 + 完成切换）
• 实践 MVVM 分层与 Repository 抽象
• 可选对接 Spring Boot API 或纯本地持久化
• 规划 TestFlight 或下一步 Swift 进阶

核心概念

项目结构

CodeRoadMapTodo/
├── App/
│   └── CodeRoadMapTodoApp.swift
├── Models/
│   └── TodoItem.swift
├── ViewModels/
│   └── TodoListViewModel.swift
├── Views/
│   ├── TodoListView.swift
│   └── TodoRowView.swift
├── Services/
│   ├── TodoRepository.swift
│   └── APIClient.swift
└── Tests/
    └── TodoListViewModelTests.swift

Model 与 ViewModel

struct TodoItem: Identifiable, Codable, Equatable {
    let id: UUID
    var title: String
    var isCompleted: Bool
    var createdAt: Date
}

@MainActor
final class TodoListViewModel: ObservableObject {
    @Published var items: [TodoItem] = []
    @Published var newTitle = ""
    @Published var isLoading = false
    @Published var errorMessage: String?

    private let repository: TodoRepositoryProtocol

    init(repository: TodoRepositoryProtocol = TodoRepository()) {
        self.repository = repository
    }

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

    func addTodo() async {
        let title = newTitle.trimmingCharacters(in: .whitespaces)
        guard !title.isEmpty else { return }
        let item = TodoItem(id: UUID(), title: title, isCompleted: false, createdAt: .now)
        do {
            try await repository.save(item)
            items.append(item)
            newTitle = ""
        } catch {
            errorMessage = error.localizedDescription
        }
    }

    func toggle(_ item: TodoItem) async {
        var updated = item
        updated.isCompleted.toggle()
        try? await repository.save(updated)
        if let idx = items.firstIndex(where: { $0.id == item.id }) {
            items[idx] = updated
        }
    }

    func delete(at offsets: IndexSet) async {
        for index in offsets {
            let item = items[index]
            try? await repository.delete(item)
        }
        items.remove(atOffsets: offsets)
    }
}

SwiftUI 主界面