Adaptive Layout：关键概念、尺寸类别和限定符

// 使用 Size Classes 的自适应控制器
import UIKit

final class AdaptiveViewController: UIViewController {

    private let compactStack = UIStackView()
    private let regularStack = UIStackView()
    private let sidebar = UIView()
    private let content = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()
        setupViews()
        updateLayout(for: traitCollection)
    }

    override func traitCollectionDidChange(
        _ previousTraitCollection: UITraitCollection?
    ) {
        super.traitCollectionDidChange(previousTraitCollection)
        if traitCollection.horizontalSizeClass
            != previousTraitCollection?.horizontalSizeClass {
            updateLayout(for: traitCollection)
        }
    }

    private func updateLayout(for traits: UITraitCollection) {
        if traits.horizontalSizeClass == .regular {
            showRegularLayout() // iPad：侧边栏 + 内容
        } else {
            showCompactLayout() // iPhone：标签栏 + push
        }
    }

    private func showRegularLayout() {
        view.subviews.forEach { $0.removeFromSuperview() }
        regularStack.addArrangedSubview(sidebar)
        regularStack.addArrangedSubview(content)
        regularStack.frame = view.bounds
        regularStack.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        view.addSubview(regularStack)
    }

    private func showCompactLayout() {
        view.subviews.forEach { $0.removeFromSuperview() }
        compactStack.addArrangedSubview(content)
        compactStack.frame = view.bounds
        compactStack.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        view.addSubview(compactStack)
    }

    private func setupViews() {
        sidebar.backgroundColor = .systemGray6
        content.backgroundColor = .systemBackground
        compactStack.axis = .vertical
        regularStack.axis = .horizontal
    }
}

// 通过 Jetpack WindowManager 进行自适应
import androidx.window.core.layout.WindowHeightSizeClass
import androidx.window.core.layout.WindowSizeClass
import androidx.window.core.layout.WindowWidthSizeClass

@OptIn(ExperimentalLayoutApi::class)
@Composable
fun AdaptiveScreen() {
    val windowSizeClass = currentWindowAdaptiveInfo().windowSizeClass

    FlowRow(
        verticalAlignment = Arrangement.Top,
        horizontalArrangement = when (windowSizeClass.windowWidthSizeClass) {
            WindowWidthSizeClass.EXPANDED -> Arrangement.SpaceEvenly
            else -> Arrangement.Start
        }
    ) {
        when (windowSizeClass.windowWidthSizeClass) {
            WindowWidthSizeClass.COMPACT -> {
                CompactContent()
            }
            WindowWidthSizeClass.MEDIUM -> {
                MediumContent()
            }
            WindowWidthSizeClass.EXPANDED -> {
                ExpandedContent()
            }
        }
    }
}

@Composable
private fun CompactContent() {
    Column(modifier = Modifier.padding(16.dp)) {
        Text("手机", style = MaterialTheme.typography.headlineSmall)
        ListContent()
    }
}

@Composable
private fun MediumContent() {
    Row(modifier = Modifier.padding(24.dp)) {
        NavigationRail { ... }
        Column { ListContent() }
    }
}

@Composable
private fun ExpandedContent() {
    Row(modifier = Modifier.padding(32.dp)) {
        PermanentNavigationDrawer { ... }
        Column {
            ListContent()
        }
        DetailPane()
    }
}

// 通过 AnyLayout 和 ViewThatFits 进行 SwiftUI 自适应
import SwiftUI

struct AdaptiveGrid: View {
    @Environment(\.horizontalSizeClass) private var hSizeClass

    var body: some View {
        let layout = hSizeClass == .regular
            ? AnyLayout(HStackLayout())
            : AnyLayout(VStackLayout())

        layout {
            Label("收藏", systemImage: "star")
            Label("最近", systemImage: "clock")
            Label("设置", systemImage: "gear")
        }
        .padding()
    }
}

// ViewThatFits — 自动选择布局
struct SmartLayout: View {
    var body: some View {
        ViewThatFits {
            HStack { // 优先级 1：水平
                CardView()
                CardView()
            }
            VStack { // 如果放不下 — 垂直
                CardView()
                CardView()
            }
        }
    }
}

// 通过 BoxWithConstraints 进行 Jetpack Compose 自适应
@Composable
fun AdaptiveList(items: List<String>) {
    BoxWithConstraints {
        val width = maxWidth

        if (width >= 600.dp) {
            // 平板：两列（list-detail）
            Row(modifier = Modifier.fillMaxSize()) {
                LazyColumn(modifier = Modifier.weight(1f)) {
                    items(items) { item ->
                        ListItem(text = item)
                    }
                }
                var selected by remember { mutableStateOf(items.first()) }
                DetailPanel(item = selected)
                    .weight(2f)
            }
        } else {
            // 手机：带导航的单列
            LazyColumn(modifier = Modifier.fillMaxSize()) {
                items(items) { item ->
                    ListItem(text = item, onClick = { navigateToDetail(item) })
                }
            }
        }
    }
}

@Composable
fun AdaptiveListMaterial3() {
    val windowClass = currentWindowAdaptiveInfo().windowSizeClass

    AdaptiveLayout(
        layout = windowClass.windowWidthSizeClass
    ) {
        when (windowClass.windowWidthSizeClass) {
            WindowWidthSizeClass.COMPACT -> {
                ListDetailScaffold(
                    isDetailOnly = false,
                    list = { ListPane() },
                    detail = { DetailPane() }
                )
            }
            else -> {
                ListDetailScaffold(
                    isDetailOnly = false,
                    list = { ListPane() },
                    detail = { DetailPane() }
                )
            }
        }
    }
}