UIKit Core

UIKit是iOS的核心UI框架，提供声明式和程序式界面构建能力。

Reference Loading Guide

ALWAYS load reference files if there is even a small chance the content may be required.

Core Concepts

UIViewController Lifecycle

class MyViewController: UIViewController {

    override func loadView() {
        // Custom view loading (rarely needed)
        super.loadView()
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Called once when view hierarchy loaded
        // Setup UI, configure initial state
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        // Called before view appears
        // Update UI, start animations
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        // Called when view fully visible
        // Start network requests, timers
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        // Called before view disappears
        // Save state, cleanup
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        // Called when view fully hidden
        // Stop network requests, timers
    }

    deinit {
        // Cleanup notifications, observers
    }
}

Auto Layout with Anchors (iOS 9+)

// Preferred: Modern anchor API
view.translatesAutoresizingMaskIntoConstraints = false

NSLayoutConstraint.activate([
    view.topAnchor.constraint(equalTo: superview.topAnchor, constant: 20),
    view.leadingAnchor.constraint(equalTo: superview.leadingAnchor, constant: 16),
    view.trailingAnchor.constraint(equalTo: superview.trailingAnchor, constant: -16),
    view.heightAnchor.constraint(equalToConstant: 44)
])

Custom UIView Pattern

final class CustomView: UIView {

    // MARK: - Subviews

    private let titleLabel: UILabel = {
        let label = UILabel()
        label.translatesAutoresizingMaskIntoConstraints = false
        label.font = .systemFont(ofSize: 17, weight: .semibold)
        return label
    }()

    // MARK: - Initialization

    override init(frame: CGRect) {
        super.init(frame: frame)
        setupView()
        setupConstraints()
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        setupView()
        setupConstraints()
    }

    // MARK: - Setup

    private func setupView() {
        addSubview(titleLabel)
        backgroundColor = .systemBackground
    }

    private func setupConstraints() {
        NSLayoutConstraint.activate([
            titleLabel.centerXAnchor.constraint(equalTo: centerXAnchor),
            titleLabel.centerYAnchor.constraint(equalTo: centerYAnchor)
        ])
    }

    // MARK: - Configuration

    func configure(with title: String) {
        titleLabel.text = title
    }
}

UITableView Pattern

class MyViewController: UIViewController {

    private let tableView: UITableView = {
        let table = UITableView(frame: .zero, style: .plain)
        table.translatesAutoresizingMaskIntoConstraints = false
        table.register(UITableViewCell.self, forCellReuseIdentifier: "Cell")
        return table
    }()

    private var items: [String] = []

    override func viewDidLoad() {
        super.viewDidLoad()
        setupTableView()
    }

    private func setupTableView() {
        view.addSubview(tableView)

        NSLayoutConstraint.activate([
            tableView.topAnchor.constraint(equalTo: view.topAnchor),
            tableView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            tableView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            tableView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ])

        tableView.dataSource = self
        tableView.delegate = self
    }
}

extension MyViewController: UITableViewDataSource {
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return items.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
        cell.textLabel?.text = items[indexPath.row]
        return cell
    }
}

extension MyViewController: UITableViewDelegate {
    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        tableView.deselectRow(at: indexPath, animated: true)
        // Handle selection
    }
}

UIKit Animation

// Simple property animation
UIView.animate(withDuration: 0.3) {
    view.alpha = 1.0
    view.frame = newFrame
}

// Spring animation
UIView.animate(withDuration: 0.5,
               delay: 0,
               usingSpringWithDamping: 0.7,
               initialSpringVelocity: 0.5,
               options: .curveEaseInOut)
{
    view.transform = .identity
}

// Transition
UIView.transition(from: oldView,
                to: newView,
                duration: 0.3,
                options: .transitionCrossDissolve)

Delegate Pattern (Weak Reference)

protocol MyViewControllerDelegate: AnyObject {
    func myViewController(_ controller: MyViewController, didCompleteWith result: Result)
}

class MyViewController: UIViewController {
    weak var delegate: MyViewControllerDelegate?

    private func notifyCompletion() {
        delegate?.myViewController(self, didCompleteWith: .success)
    }
}

Common Mistakes

1. 在错误线程操作UI

   • ❌ DispatchQueue.global.async { self.view.backgroundColor = .red }
   • ✅ DispatchQueue.main.async { self.view.backgroundColor = .red }
   • ✅ 使用 @MainActor 标记类

2. Memory Leaks - Delegate使用strong引用

   • ❌ var delegate: MyViewControllerDelegate?
   • ✅ weak var delegate: MyViewControllerDelegate?

3. 约束冲突

   • 使用优先级解决冲突：.priority = .defaultHigh
   • 避免硬编码约束值
   • 使用 intrinsicContentSize 和 contentHugging

4. UITableView性能问题

   • 复用cell：dequeueReusableCell(withIdentifier:for:)
   • 避免复杂的cell配置
   • 使用 estimatedRowHeight 优化滚动

5. 忘记调用super

   override func viewWillAppear(_ animated: Bool) {
       super.viewWillAppear(animated) // ✅ 必须
       // custom code
   }
   

Best Practices

1. 使用 translatesAutoresizingMaskIntoConstraints = false

   view.translatesAutoresizingMaskIntoConstraints = false
   

2. Lazy初始化子视图

   private let label: UILabel = {
       let label = UILabel()
       label.translatesAutoresizingMaskIntoConstraints = false
       return label
   }()
   

3. Extension组织代码

   // MARK: - UITableViewDataSource
   extension MyViewController: UITableViewDataSource { }
   
   // MARK: - UITableViewDelegate
   extension MyViewController: UITableViewDelegate { }
   

4. 考虑iPad布局

   • 使用trait collection变化
   • 自适应布局
   • 考虑split view

5. 无障碍支持

   button.accessibilityLabel = "Add item"
   button.accessibilityHint = "Adds a new item to the list"
   button.isAccessibilityElement = true
   

Swift 6 Concurrency

@MainActor
class MyViewController: UIViewController {

    private var task: Task<Void, Never>?

    func loadData() async {
        task?.cancel()
        task = Task {
            do {
                let data = try await networkService.fetch()
                await MainActor.run {
                    self.updateUI(with: data)
                }
            } catch {
                await MainActor.run {
                    self.showError(error)
                }
            }
        }
    }

    deinit {
        task?.cancel()
    }
}

Quick Reference