JetpackCompose Scaffold组件使用教程

data class Item(
    val name: String,
    val icon: Int
)

@Composable
fun mainBody() {
    // 存储当前选中的底部按钮的状态
    var selectedItem by remember {
        mutableStateOf(0)
    }
    // 三个底部按钮
    val items = listOf(
        Item("主页", R.drawable.home),
        Item("列表", R.drawable.list),
        Item("设置", R.drawable.setting)
    )
    ...
}

Scaffold(
    topBar = {
        TopAppBar(
            title = { Text("主页") },
            navigationIcon = {
                IconButton(onClick = { /*TODO*/ }) {
                    Icon(Icons.Filled.Menu, null)
                }
            }
        )
    },
    ...
){}

bottomBar = {
    BottomNavigation {
        items.forEachIndexed { index, item ->
            BottomNavigationItem(
                // selectedItem 是内置属性，表示当前选中的Item
                // onClick即切换当前激活的Item
                selected = selectedItem == index,
                onClick = { selectedItem = index },
                // 这几个属性看看英文就懂了，不解释
                icon = { Icon(painterResource(item.icon), null) },
                alwaysShowLabel = false,
                label = { Text(item.name) }
            )
        }
    }
}

@Composable
fun mainBody() {
    var selectedItem by remember {
        mutableStateOf(0)
    }
    val items = listOf(
        Item("主页", R.drawable.home),
        Item("列表", R.drawable.list),
        Item("设置", R.drawable.setting)
    )
    Scaffold(
        topBar = {
            TopAppBar(
                title = { Text("主页") },
                navigationIcon = {
                    IconButton(onClick = { /*TODO*/ }) {
                        Icon(Icons.Filled.Menu, null)
                    }
                }
            )
        },
        bottomBar = {
            BottomNavigation {
                items.forEachIndexed { index, item ->
                    BottomNavigationItem(
                        selected = selectedItem == index,
                        onClick = { selectedItem = index },
                        icon = { Icon(painterResource(item.icon), null) },
                        alwaysShowLabel = false,
                        label = { Text(item.name) }
                    )
                }
            }
        }
    ) {
        // 在scaffold里面塞一个box，糊弄一下
        Box(
            modifier = Modifier.fillMaxSize(),
            contentAlignment = Alignment.Center
        ) {
            Text(text = "主页界面")
        }
    }
}