React 18 与 Swift 5.7 基础原理对比与实践指南
1. 渲染系统对比
1.1 React 18 并发渲染与 Swift 5.7 异步渲染
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import { createRoot } from 'react-dom/client';
import { useTransition, useDeferredValue } from 'react';
function TodoList() {
const [todos, setTodos] = useState([]);
const [isPending, startTransition] = useTransition();
const deferredTodos = useDeferredValue(todos);
return (
<div className="todo-list">
{isPending ? (
<LoadingSpinner />
) : (
deferredTodos.map(todo => (
<TodoItem key={todo.id} {...todo} />
))
)}
</div>
);
}
const container = document.getElementById('root');
const root = createRoot(container);
root.render(<TodoList />);
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@MainActor
class TodoListViewController: UIViewController {
private let tableView: UITableView = {
let table = UITableView()
table.register(TodoCell.self, forCellReuseIdentifier: "TodoCell")
return table
}()
private var todos: [Todo] = []
private var isLoading = false
override func viewDidLoad() {
super.viewDidLoad()
tableView.dataSource = self
tableView.delegate = self
}
func loadTodos() async {
isLoading = true
tableView.reloadData()
todos = await TodoService.shared.fetchTodos()
isLoading = false
tableView.reloadData()
}
}
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原理对比：
React 18 并发渲染：
- 使用 Fiber 架构实现并发渲染
- 支持优先级调度和中断
- 使用 useTransition 和 useDeferredValue 控制更新优先级
- 自动批处理状态更新
Swift 5.7 异步渲染：
- 使用 async/await 处理异步操作
- 支持结构化并发
- 使用 @MainActor 确保 UI 更新在主线程
- 支持任务优先级和取消
1.2 状态更新机制
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function Counter() {
const [count, setCount] = useState(0);
function handleClick() {
setCount(c => c + 1);
setCount(c => c + 1);
}
const [isPending, startTransition] = useTransition();
function handleExpensiveUpdate() {
startTransition(() => {
setCount(c => c + 1);
});
}
}
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@MainActor
class CounterViewController: UIViewController {
@Published private(set) var count: Int = 0
private var cancellables = Set<AnyCancellable>()
override func viewDidLoad() {
super.viewDidLoad()
$count
.receive(on: RunLoop.main)
.sink { [weak self] newCount in
self?.updateUI(count: newCount)
}
.store(in: &cancellables)
}
func handleClick() {
withAnimation {
count += 1
count += 1
}
}
func handleExpensiveUpdate() async {
await Task.detached(priority: .background) {
await MainActor.run {
self.count += 1
}
}.value
}
}
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2. 实际项目应用
2.1 列表性能优化
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import { useVirtualizer } from '@tanstack/react-virtual';
function VirtualList({ items }) {
const parentRef = useRef();
const rowVirtualizer = useVirtualizer({
count: items.length,
getScrollElement: () => parentRef.current,
estimateSize: () => 50,
overscan: 5
});
return (
<div ref={parentRef} style={{ height: '100vh', overflow: 'auto' }}>
<div
style={{
height: `${rowVirtualizer.getTotalSize()}px`,
width: '100%',
position: 'relative'
}}
>
{rowVirtualizer.getVirtualItems().map((virtualRow) => (
<div
key={virtualRow.index}
style={{
position: 'absolute',
top: 0,
left: 0,
width: '100%',
height: `${virtualRow.size}px`,
transform: `translateY(${virtualRow.start}px)`
}}
>
{items[virtualRow.index].content}
</div>
))}
</div>
</div>
);
}
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@MainActor
class OptimizedTableViewController: UIViewController {
private let tableView: UITableView = {
let table = UITableView()
table.register(OptimizedCell.self, forCellReuseIdentifier: "Cell")
return table
}()
private var items: [Item] = []
private var cellHeights: [IndexPath: CGFloat] = [:]
override func viewDidLoad() {
super.viewDidLoad()
tableView.dataSource = self
tableView.delegate = self
Task {
await calculateCellHeights()
}
}
private func calculateCellHeights() async {
await withTaskGroup(of: Void.self) { group in
for (index, item) in items.enumerated() {
group.addTask {
let indexPath = IndexPath(row: index, section: 0)
let height = await self.calculateHeight(for: item)
await MainActor.run {
self.cellHeights[indexPath] = height
}
}
}
}
tableView.reloadData()
}
}
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2.2 状态管理实践
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import { createContext, useContext, useReducer, useCallback } from 'react';
const TodoContext = createContext(null);
function todoReducer(state, action) {
switch (action.type) {
case 'SET_TODOS':
return { ...state, todos: action.payload };
case 'SET_FILTER':
return { ...state, filter: action.payload };
default:
return state;
}
}
function TodoProvider({ children }) {
const [state, dispatch] = useReducer(todoReducer, {
todos: [],
filter: 'all'
});
const filteredTodos = useMemo(() => {
return state.todos.filter(todo => {
if (state.filter === 'all') return true;
if (state.filter === 'active') return !todo.completed;
if (state.filter === 'completed') return todo.completed;
});
}, [state.todos, state.filter]);
const updateTodos = useCallback((todos) => {
dispatch({ type: 'SET_TODOS', payload: todos });
}, []);
return (
<TodoContext.Provider value={{ todos: filteredTodos, updateTodos }}>
{children}
</TodoContext.Provider>
);
}
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@MainActor
class TodoManager: ObservableObject {
static let shared = TodoManager()
@Published private(set) var todos: [Todo] = []
@Published private(set) var filter: TodoFilter = .all
var filteredTodos: [Todo] {
todos.filter { todo in
switch filter {
case .all: return true
case .active: return !todo.completed
case .completed: return todo.completed
}
}
}
func updateTodos(_ newTodos: [Todo]) async {
todos = newTodos
objectWillChange.send()
}
func setFilter(_ newFilter: TodoFilter) {
filter = newFilter
objectWillChange.send()
}
}
extension TodoManager {
func fetchTodos() async throws -> [Todo] {
let url = URL(string: "https://api.example.com/todos")!
let (data, _) = try await URLSession.shared.data(from: url)
return try JSONDecoder().decode([Todo].self, from: data)
}
}
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3. 性能监控实践
3.1 React 18 性能监控
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| import { Profiler } from 'react';
function ProfilerExample() {
return (
<Profiler id="App" onRender={onRenderCallback}>
<App />
</Profiler>
);
}
function onRenderCallback(
id,
phase,
actualDuration,
baseDuration,
startTime,
commitTime,
interactions
) {
console.log({
id,
phase,
actualDuration,
baseDuration,
startTime,
commitTime,
interactions
});
}
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3.2 Swift 5.7 性能监控
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| @MainActor
class PerformanceMonitor {
static let shared = PerformanceMonitor()
private var displayLink: CADisplayLink?
private var lastTimestamp: CFTimeInterval = 0
private var frameDrops: [CFTimeInterval] = []
func startMonitoring() {
displayLink = CADisplayLink(target: self, selector: #selector(displayLinkFired))
displayLink?.preferredFrameRateRange = CAFrameRateRange(minimum: 60, maximum: 120, preferred: 60)
displayLink?.add(to: .main, forMode: .common)
}
@objc private func displayLinkFired(_ link: CADisplayLink) {
let currentTimestamp = link.timestamp
let frameDuration = currentTimestamp - lastTimestamp
lastTimestamp = currentTimestamp
if frameDuration > 1/60 {
frameDrops.append(frameDuration)
print("Frame drop detected: \(frameDuration)")
}
}
func generateReport() async -> PerformanceReport {
await withCheckedContinuation { continuation in
let report = PerformanceReport(
frameDrops: frameDrops,
averageFrameDuration: frameDrops.reduce(0, +) / Double(frameDrops.count)
)
continuation.resume(returning: report)
}
}
}
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4. 总结
React 18 和 Swift 5.7 在基础原理和实际应用上有很多相似之处：
并发处理：
- React 18 的并发渲染和优先级调度
- Swift 5.7 的 async/await 和结构化并发
状态管理：
- React 18 的 Context 和 Hooks
- Swift 5.7 的 @Published 和 Combine 框架
性能优化：
- React 18 的虚拟列表和自动批处理
- Swift 5.7 的异步渲染和任务优先级
性能监控：
- React 18 的 Profiler 和 DevTools
- Swift 5.7 的 Instruments 和性能分析工具
通过理解这些对应关系，iOS 开发者可以更快地掌握 React 18 开发，并在实际项目中应用这些最佳实践。