iOS SwiftUI核心技术实战指南：移动应用开发的关键知识点与技巧

struct ToggleText: View {
    @State private var isOn = false // 管理视图内部状态

    var body: some View {
        VStack {
            Text(isOn ? "开启" : "关闭") // 根据状态显示结果
            Button("切换状态") {
                isOn.toggle() // 修改状态，视图自动更新
            }
        }
    }
}

HStack(alignment: .top, spacing: 12) { // 水平排列，顶部对齐，子视图间距12
    Image("avatar")
        .resizable()
        .frame(width: 60, height: 60)
        .clipShape(Circle()) // 圆形头像

    VStack(alignment: .leading, spacing: 4) { // 垂直排列，左对齐，间距4
        Text("张三")
            .font(.headline)
        Text("一名SwiftUI开发者")
            .font(.subheadline)
            .foregroundColor(.gray)
    }

    Spacer() // 推挤子视图到左侧，占据剩余空间
}
.padding() // 整体内边距

Button("确认") { }
    .frame(maxWidth: .infinity) // 宽度占满父视图
    .padding()
    .background(Color.blue)
    .foregroundColor(.white)
    .cornerRadius(8)

// 错误示例：视图重新渲染时ViewModel被重置
struct ContentView: View {
    @ObservedObject var viewModel = TodoViewModel() // 每次渲染都新建

    var body: some View {
        TodoList(viewModel: viewModel)
    }
}

// 正确示例：保持ViewModel的生命周期与视图一致
struct ContentView: View {
    @StateObject var viewModel = TodoViewModel() // 只创建一次

    var body: some View {
        TodoList(viewModel: viewModel)
    }
}

struct ParentView: View {
    @State private var isNotificationOn = false // 父视图的状态

    var body: some View {
        VStack {
            Text("通知状态：(isNotificationOn ? "开启" : "关闭")")
            ChildToggle(isOn: $isNotificationOn) // 传递绑定
        }
    }
}

struct ChildToggle: View {
    @Binding var isOn: Bool // 接收父视图的绑定

    var body: some View {
        Toggle("开启通知", isOn: $isOn) // 绑定到开关
    }
}

struct UserProfile: View, Equatable { // 遵循Equatable协议
    let user: User

    static func == (lhs: UserProfile, rhs: UserProfile) -> Bool {
        lhs.user.id == rhs.user.id // 只有id变化时才重新渲染
    }

    var body: some View {
        Text(user.name)
    }
}

// 使用时包裹EquatableView
EquatableView(content: UserProfile(user: currentUser))

// 错误示例：body里计算复杂数组
struct ContentView: View {
    var body: some View {
        let filteredData = data.filter { $0.isActive } // 每次渲染都计算
        List(filteredData) { item in
            Text(item.name)
        }
    }
}

// 正确示例：用@State或@ObservedObject缓存计算结果
struct ContentView: View {
    @State private var filteredData: [Item] = []

    var body: some View {
        List(filteredData) { item in
            Text(item.name)
        }
        .onAppear {
            filteredData = data.filter { $0.isActive } // 只计算一次
        }
    }
}

struct TodoItem: Identifiable, Codable { // Identifiable用于List，Codable用于存储
    let id = UUID() // 唯一标识
    var title: String // 待办内容
    var isCompleted: Bool // 是否完成
}

struct TodoList: View {
    @State private var todos: [TodoItem] = [] // 待办列表
    @State private var newTodoTitle = "" // 新待办输入框文字

    var body: some View {
        NavigationStack { // iOS 16+的导航组件
            VStack(spacing: 16) {
                // 输入框+添加按钮
                HStack {
                    TextField("输入待办项", text: $newTodoTitle)
                        .textFieldStyle(.roundedBorder)

                    Button("添加") {
                        guard !newTodoTitle.isEmpty else { return }
                        let newTodo = TodoItem(title: newTodoTitle, isCompleted: false)
                        todos.append(newTodo)
                        newTodoTitle = "" // 清空输入框
                    }
                    .buttonStyle(.borderedProminent)
                }

                // 待办列表
                List($todos) { $todo in // 绑定到每个待办项
                    HStack {
                        Toggle("", isOn: $todo.isCompleted) // 标记完成
                        Text(todo.title)
                            .strikethrough(todo.isCompleted, color: .gray) // 完成时划线
                    }
                }
            }
            .padding()
            .navigationTitle("待办清单")
            // 加载/保存数据
            .onAppear { loadTodos() }
            .onChange(of: todos) { _ in saveTodos() }
        }
    }

    // 从UserDefaults加载数据
    func loadTodos() {
        guard let data = UserDefaults.standard.data(forKey: "todos") else { return }
        if let decoded = try? JSONDecoder().decode([TodoItem].self, from: data) {
            todos = decoded
        }
    }

    // 保存数据到UserDefaults
    func saveTodos() {
        guard let data = try? JSONEncoder().encode(todos) else { return }
        UserDefaults.standard.set(data, forKey: "todos")
    }
}

List($todos) { $todo in
    // ... 原有内容
}
.onDelete(perform: deleteTodo)

// 删除逻辑
func deleteTodo(at offsets: IndexSet) {
    todos.remove(atOffsets: offsets)
}