如何为Jetpack Compose的Scaffold PaddingValues添加默认水平内边距？

最简便的方式是自定义一个封装了默认内边距的Scaffold组件，这样所有页面直接使用这个自定义组件，不用重复编写水平内边距代码。

步骤1：封装自定义Scaffold组件 #

创建一个AppScaffold函数，完全兼容原生Scaffold的所有参数，同时在内部自动合并Scaffold的padding和默认水平内边距：

@Composable
fun AppScaffold(
    topBar: @Composable () -> Unit = {},
    bottomBar: @Composable () -> Unit = {},
    snackbarHost: @Composable () -> Unit = {},
    floatingActionButton: @Composable () -> Unit = {},
    floatingActionButtonPosition: FabPosition = FabPosition.End,
    isFloatingActionButtonDocked: Boolean = false,
    drawerContent: @Composable (ColumnScope.() -> Unit)? = null,
    drawerGesturesEnabled: Boolean = true,
    drawerShape: Shape = MaterialTheme.shapes.large,
    drawerElevation: Dp = DrawerDefaults.Elevation,
    drawerBackgroundColor: Color = MaterialTheme.colors.surface,
    drawerContentColor: Color = contentColorFor(drawerBackgroundColor),
    drawerScrimColor: Color = DrawerDefaults.scrimColor,
    backgroundColor: Color = MaterialTheme.colors.background,
    contentColor: Color = contentColorFor(backgroundColor),
    // 可选：允许全局或局部覆盖默认水平内边距
    horizontalPadding: Dp = 16.dp,
    content: @Composable (PaddingValues) -> Unit
) {
    Scaffold(
        topBar = topBar,
        bottomBar = bottomBar,
        snackbarHost = snackbarHost,
        floatingActionButton = floatingActionButton,
        floatingActionButtonPosition = floatingActionButtonPosition,
        isFloatingActionButtonDocked = isFloatingActionButtonDocked,
        drawerContent = drawerContent,
        drawerGesturesEnabled = drawerGesturesEnabled,
        drawerShape = drawerShape,
        drawerElevation = drawerElevation,
        drawerBackgroundColor = drawerBackgroundColor,
        drawerContentColor = drawerContentColor,
        drawerScrimColor = drawerScrimColor,
        backgroundColor = backgroundColor,
        contentColor = contentColor
    ) { scaffoldPadding ->
        // 合并原生padding和自定义水平内边距
        val combinedPadding = scaffoldPadding.copy(
            start = scaffoldPadding.start + horizontalPadding,
            end = scaffoldPadding.end + horizontalPadding
        )
        content(combinedPadding)
    }
}

步骤2：替换原生Scaffold使用自定义组件 #

在所有需要Scaffold的页面，直接用AppScaffold替代原生Scaffold，无需额外添加水平内边距：

AppScaffold(topBar = {
    TopAppBar(title = { Text("...") })
}) { paddingValues ->
    Column(modifier = Modifier.padding(paddingValues)) {
        // 这里的内容自动带有默认16.dp的左右内边距
        Text("示例文本")
        Switch(checked = true, onCheckedChange = {})
    }
}

灵活调整内边距 #

如果某个页面需要不同的内边距，直接传入horizontalPadding参数覆盖默认值即可：

AppScaffold(
    topBar = { TopAppBar(title = { Text("特殊页面") }) },
    horizontalPadding = 20.dp
) { paddingValues ->
    Column(modifier = Modifier.padding(paddingValues)) {
        // 这里左右内边距为20.dp
    }
}

内容的提问来源于stack exchange，提问作者J. Doe