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构建辅助窗格布局

辅助窗格布局可让用户专注于应用的主要内容，同时显示相关的辅助信息。例如，主窗格可能会显示电影的详细信息，而辅助窗格则会列出类似电影、同一导演执导的电影或由同一演员主演的作品。

实现具有基架的辅助窗格

NavigableSupportingPaneScaffold 是一个可组合项，可简化在 Jetpack Compose 中实现辅助窗格布局的过程。它封装了 SupportingPaneScaffold，并添加了内置导航和预测性返回处理。

辅助窗格基架最多支持三个窗格：

主窗格：显示主要内容。
辅助窗格：提供与主窗格相关的其他上下文或工具。
额外窗格（可选）：在需要时用于显示补充内容。

该脚手架会根据窗口大小进行自适应：

在较大窗口中，主要窗格和辅助窗格并排显示。
在小窗口中，一次只能看到一个窗格，并随着用户浏览而切换。

图 1. 辅助窗格布局。

添加依赖项

NavigableSupportingPaneScaffold 是 Material 3 自适应布局库的一部分。

将以下三个相关依赖项添加到应用或模块的 build.gradle 文件中：

Kotlin

implementation("androidx.compose.material3.adaptive:adaptive")
implementation("androidx.compose.material3.adaptive:adaptive-layout")
implementation("androidx.compose.material3.adaptive:adaptive-navigation")

Groovy

implementation 'androidx.compose.material3.adaptive:adaptive'
implementation 'androidx.compose.material3.adaptive:adaptive-layout'
implementation 'androidx.compose.material3.adaptive:adaptive-navigation'

adaptive：低级构建块，例如 HingeInfo 和 Posture
adaptive-layout：自适应布局，例如 ListDetailPaneScaffold 和 SupportingPaneScaffold
adaptive-navigation：用于在窗格内和窗格之间导航的可组合项，以及默认支持导航的自适应布局，例如 NavigableListDetailPaneScaffold 和 NavigableSupportingPaneScaffold

验证您的项目是否包含 compose-material3-adaptive 1.1.0-beta1 或更高版本。

选择启用预测性返回手势

如需在 Android 15 或更低版本中启用预测性返回动画，您必须选择启用对预测性返回手势的支持。如需选择启用，请将 android:enableOnBackInvokedCallback="true" 添加到 AndroidManifest.xml 文件中的 <application> 标记或各个 <activity> 标记。

当应用以 Android 16（API 级别 36）或更高版本为目标平台时，系统会默认启用预测性返回手势。

创建导航器

在小窗口中，一次只能显示一个窗格，因此请使用 ThreePaneScaffoldNavigator 在窗格之间切换。使用 rememberSupportingPaneScaffoldNavigator 创建导航器的实例。

val scaffoldNavigator = rememberSupportingPaneScaffoldNavigator()
val scope = rememberCoroutineScope()
SampleSupportingPaneScaffold.kt

将导航器传递给 Scaffold

Scaffold 需要 ThreePaneScaffoldNavigator（表示 Scaffold 状态的接口）、ThreePaneScaffoldValue 和 PaneScaffoldDirective。

NavigableSupportingPaneScaffold(
    navigator = scaffoldNavigator,
    mainPane = { /*...*/ },
    supportingPane = { /*...*/ },
)SampleSupportingPaneScaffold.kt

主窗格和辅助窗格是包含内容的可组合项。使用 AnimatedPane 在导航期间应用默认窗格动画。使用 scaffold 值检查辅助窗格是否处于隐藏状态；如果是，则显示一个按钮，用于调用 navigateTo(SupportingPaneScaffoldRole.Supporting) 以显示辅助窗格。

对于大屏设备，请使用 ThreePaneScaffoldNavigator.navigateBack() 方法关闭辅助窗格，并传入 BackNavigationBehavior.PopUntilScaffoldValueChange 常量。调用此方法会强制重组 NavigableSupportingPaneScaffold。在重组期间，检查 ThreePaneScaffoldNavigator.currentDestination 属性以确定是否显示辅助窗格。

以下是 Scaffold 的完整实现：

val scaffoldNavigator = rememberSupportingPaneScaffoldNavigator()
val scope = rememberCoroutineScope()
val backNavigationBehavior = BackNavigationBehavior.PopUntilScaffoldValueChange

NavigableSupportingPaneScaffold(
    navigator = scaffoldNavigator,
    mainPane = {
        AnimatedPane(
            modifier = Modifier
                .safeContentPadding()
                .background(Color.Red)
        ) {
            if (scaffoldNavigator.scaffoldValue[SupportingPaneScaffoldRole.Supporting] == PaneAdaptedValue.Hidden) {
                Button(
                    modifier = Modifier
                        .wrapContentSize(),
                    onClick = {
                        scope.launch {
                            scaffoldNavigator.navigateTo(SupportingPaneScaffoldRole.Supporting)
                        }
                    }
                ) {
                    Text("Show supporting pane")
                }
            } else {
                Text("Supporting pane is shown")
            }
        }
    },
    supportingPane = {
        AnimatedPane(modifier = Modifier.safeContentPadding()) {
            Column {
                // Allow users to dismiss the supporting pane. Use back navigation to
                // hide an expanded supporting pane.
                if (scaffoldNavigator.scaffoldValue[SupportingPaneScaffoldRole.Supporting] == PaneAdaptedValue.Expanded) {
                    // Material design principles promote the usage of a right-aligned
                    // close (X) button.
                    IconButton(
                        modifier =  Modifier.align(Alignment.End).padding(16.dp),
                        onClick = {
                            scope.launch {
                                scaffoldNavigator.navigateBack(backNavigationBehavior)
                            }
                        }
                    ) {
                        Icon(Icons.Default.Close, contentDescription = "Close")
                    }
                }
                Text("Supporting pane")
            }

        }
    }
)SampleSupportingPaneScaffold.kt

提取窗格可组合项

将 SupportingPaneScaffold 的各个窗格提取到各自的可组合项中，使其可重复使用和测试。如果您希望使用默认动画，请使用 ThreePaneScaffoldScope 访问 AnimatedPane：

@OptIn(ExperimentalMaterial3AdaptiveApi::class)
@Composable
fun ThreePaneScaffoldPaneScope.MainPane(
    shouldShowSupportingPaneButton: Boolean,
    onNavigateToSupportingPane: () -> Unit,
    modifier: Modifier = Modifier,
) {
    AnimatedPane(
        modifier = modifier.safeContentPadding()
    ) {
        // Main pane content
        if (shouldShowSupportingPaneButton) {
            Button(onClick = onNavigateToSupportingPane) {
                Text("Show supporting pane")
            }
        } else {
            Text("Supporting pane is shown")
        }
    }
}

@OptIn(ExperimentalMaterial3AdaptiveApi::class)
@Composable
fun ThreePaneScaffoldPaneScope.SupportingPane(
    scaffoldNavigator: ThreePaneScaffoldNavigator<Any>,
    modifier: Modifier = Modifier,
    backNavigationBehavior: BackNavigationBehavior = BackNavigationBehavior.PopUntilScaffoldValueChange,
) {
    val scope = rememberCoroutineScope()
    AnimatedPane(modifier = Modifier.safeContentPadding()) {
        Column {
            // Allow users to dismiss the supporting pane. Use back navigation to
            // hide an expanded supporting pane.
            if (scaffoldNavigator.scaffoldValue[SupportingPaneScaffoldRole.Supporting] == PaneAdaptedValue.Expanded) {
                // Material design principles promote the usage of a right-aligned
                // close (X) button.
                IconButton(
                    modifier =  modifier.align(Alignment.End).padding(16.dp),
                    onClick = {
                        scope.launch {
                            scaffoldNavigator.navigateBack(backNavigationBehavior)
                        }
                    }
                ) {
                    Icon(Icons.Default.Close, contentDescription = "Close")
                }
            }
            Text("Supporting pane")
        }

    }
}SampleSupportingPaneScaffold.kt

将这些窗格提取到可组合项中可简化 SupportingPaneScaffold 的使用（将以下内容与上一部分中 Scaffold 的完整实现进行比较）：

val scaffoldNavigator = rememberSupportingPaneScaffoldNavigator()
val scope = rememberCoroutineScope()

NavigableSupportingPaneScaffold(
    navigator = scaffoldNavigator,
    mainPane = {
        MainPane(
            shouldShowSupportingPaneButton = scaffoldNavigator.scaffoldValue.secondary == PaneAdaptedValue.Hidden,
            onNavigateToSupportingPane = {
                scope.launch {
                    scaffoldNavigator.navigateTo(ThreePaneScaffoldRole.Secondary)
                }
            }
        )
    },
    supportingPane = { SupportingPane(scaffoldNavigator = scaffoldNavigator) },
)SampleSupportingPaneScaffold.kt

如果您需要更好地控制 Scaffold 的特定方面，请考虑使用 SupportingPaneScaffold，而不是 NavigableSupportingPaneScaffold。此方法分别接受 PaneScaffoldDirective 和 ThreePaneScaffoldValue 或 ThreePaneScaffoldState。这种灵活性使您可以为窗格间距实现自定义逻辑，并确定应同时显示多少个窗格。您还可以通过添加 ThreePaneScaffoldPredictiveBackHandler 来启用预测性返回支持。

添加`ThreePaneScaffoldPredictiveBackHandler`

附加接受 Scaffold 导航器实例的预测性返回处理程序，并指定 backBehavior。这决定了在返回导航期间如何从返回堆栈中弹出目的地。然后，将 scaffoldDirective 和 scaffoldState 传递给 SupportingPaneScaffold。使用接受 ThreePaneScaffoldState 的重载，传入 scaffoldNavigator.scaffoldState。

在 SupportingPaneScaffold 中定义主窗格和辅助窗格。使用 AnimatedPane 呈现默认窗格动画。

执行完这些步骤后，您的代码应如下所示：

val scaffoldNavigator = rememberSupportingPaneScaffoldNavigator()
val scope = rememberCoroutineScope()

ThreePaneScaffoldPredictiveBackHandler(
    navigator = scaffoldNavigator,
    backBehavior = BackNavigationBehavior.PopUntilScaffoldValueChange
)

SupportingPaneScaffold(
    directive = scaffoldNavigator.scaffoldDirective,
    scaffoldState = scaffoldNavigator.scaffoldState,
    mainPane = {
        MainPane(
            shouldShowSupportingPaneButton = scaffoldNavigator.scaffoldValue.secondary == PaneAdaptedValue.Hidden,
            onNavigateToSupportingPane = {
                scope.launch {
                    scaffoldNavigator.navigateTo(ThreePaneScaffoldRole.Secondary)
                }
            }
        )
    },
    supportingPane = { SupportingPane(scaffoldNavigator = scaffoldNavigator) },
)SampleSupportingPaneScaffold.kt