5 步让 UIKit App 适配 iPhone Duo 的每一种窗口

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    // Never UIScreen.main.bounds or a static let: read the container on every layout pass.
    let widthClass = LayoutWidthClass(width: view.bounds.width)
    guard widthClass != appliedWidthClass else { return }
    appliedWidthClass = widthClass
    updateGrid(columns: widthClass.columnCount(compact: 3))   // 3 / 4 / 6
}

分级：compact ≤ 500 < medium ≤ 800 < expanded。单栏文字宽度上限用 LayoutWidthClass.maxSingleColumnContentWidth（466 pt）。对应模式 1–3。

private let railGuide = SideRailAvoidingLayoutGuide()

override func viewDidLoad() {
    super.viewDidLoad()
    railGuide.install(in: view)
    NSLayoutConstraint.activate([
        // Pin both edges: the rail is on the left in a left split view.
        tableView.leftAnchor.constraint(equalTo: railGuide.leftAnchor),
        tableView.rightAnchor.constraint(equalTo: railGuide.rightAnchor),
        tableView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
        tableView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
    ])
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    railGuide.update()
}

按视图静止位置计算，push 或返回手势时缩进不会跳动。碰不到侧轨的居中卡片得到 0。对应模式 4。

guard let rail = view.windowSideRail, let window = view.window else { return }
NSLayoutConstraint.deactivate(railConstraints)
railConstraints = SideRail.stripConstraints(for: railView, host: view, side: rail.side)
NSLayoutConstraint.activate(railConstraints)

let clearance = SideRail.statusBarClearance(in: view)   // window coordinates
let top = railView.convert(CGPoint(x: 0, y: clearance.firstUsableY), from: window).y
railButtonTop.constant = top + 16

折叠时放在 156 pt 状态栏下方；左分屏为 .railWithoutStatusBar，对齐 y 34。对应模式 5。

private let leftGuide = OcclusionAvoidingLayoutGuide(side: .left)
private let rightGuide = OcclusionAvoidingLayoutGuide(side: .right)

// in setup
leftGuide.install(in: headerView)
rightGuide.install(in: headerView)
backButton.leftAnchor.constraint(greaterThanOrEqualTo: leftGuide.leftAnchor, constant: 16).isActive = true
actionButton.rightAnchor.constraint(equalTo: rightGuide.rightAnchor, constant: -16).isActive = true

// in layoutSubviews, after the row has its frame
if leftGuide.update(row: titleRow.frame) || rightGuide.update(row: titleRow.frame) {
    setNeedsLayout()
}

只有与状态栏重叠的行会让开，下面的行保持全宽。对应模式 6。

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    sheetHeight.constant = min(contentHeight, SheetLayout.maxHeight(in: view))
}

无论状态栏在哪，面板顶边都留在图标下方 12 pt；放不下的内容在面板内滚动。对应模式 7。

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    syncLeftSideRailSafeArea()
}

只把 additionalSafeAreaInsets.left 补到缺少的量，侧轨离开时再去掉。对应模式 8。

private let hinge = HingeDivisionObserver()

override func viewDidLoad() {
    super.viewDidLoad()
    hinge.onChange = { [weak self] _ in self?.view.setNeedsLayout() }
    hinge.attach(to: view)
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    hinge.evaluate()   // size changes do not always produce a hinge update
    if let division = hinge.division, division.isVertical {
        leadingWidth.constant = division.leadingColumnMaxX
        trailingLeft.constant = division.trailingColumnMinX
    } else {
        // single-column layout
    }
}

≤ 140° 进入，> 150° 退出，进入前等铰链稳定 0.6 s。不要自己比较 UIHinge.Status。对应模式 10。

private let tent = TentPostureObserver()

override func viewDidLoad() {
    super.viewDidLoad()
    tent.onChange = { [weak self] state in
        guard state.hasHingeReading else { return }   // unknown is not "left the tent"
        state.isTent ? self?.showTentContent() : self?.hideTentContent()
    }
    tent.attach(to: view)
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    tent.evaluate()
}

帐篷页锁定到 TentOrientation.interfaceOrientationMask(for:) 给出的方向。打开竖屏方向锁时检测不到帐篷。对应模式 11。

let window = someView.window ?? WindowLookup.primaryWindow()
let scene = someView.window?.windowScene ?? WindowLookup.activeWindowScene()

优先用 view.window。查找函数会跳过辅助 key window，但多 scene 时只能猜。对应模式 12。