How to implement BottomAppBar and BottomDrawer pattern using Android Jetpack Compose?

Question

I'm building Android app with Jetpack Compose. Got stuck while trying to implement BottomAppBar with BottomDrawer pattern.

Bottom navigation drawers are modal drawers that are anchored to the bottom of the screen instead of the left or right edge. They are only used with bottom app bars. These drawers open upon tapping the navigation menu icon in the bottom app bar.

Description on material.io, and direct link to video.

I've tried using Scaffold, but it only supports side drawer. BottomDrawer appended to Scaffold content is displayed in content area and BottomDrawer doesn't cover BottomAppBar when open. Moving BottomDrawer after Scaffold function doesn't help either: BottomAppBar is covered by some invisible block and prevents clicking buttons.

I've also tried using BottomSheetScaffold, but it doesn't have BottomAppBar slot.

If Scaffold doesn't support this pattern, what would be correct way to implement it? Is it possible to extend Scaffold component? I fear that incorrect implementation from scratch might create issues later, when I'll try to implement navigation and snackbar.

Answer 1

They (Google Devs) invite you in the Jetpack Compose Layouts pathway to try adding other Material Design Components such as BottomNavigation or BottomDrawer to their respective Scaffold slots, and yet do not give you the solution.

BottomAppBar does have its own slot in Scaffold (i.e. bottomBar), but BottomDrawer does not - and seems to be designed exclusively for use with the BottomAppBar explicitly (see API documentation for the BottomDrawer).

At this point in the Jetpack Compose pathway, we've covered state hoisting, slots, modifiers, and have been thoroughly explained that from time to time we'll have to play around to see how best to stack and organize Composables - that they almost always have a naturally expressable way in which they work best that is practically intended.

Let me get us set up so that we are on the same page:

class MainActivity : ComponentActivity() {
    @ExperimentalMaterialApi
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            LayoutsCodelabTheme {
                // A surface container using the 'background' color from the theme
                Surface(color = MaterialTheme.colors.background) {
                    LayoutsCodelab()
                }
            }
        }
    }
}

That's the main activity calling our primary/core Composable. This is just like in the codelab with the exception of the @ExperimentalMaterialApi annotation.

Next is our primary/core Composable:

@ExperimentalMaterialApi
@Composable
fun LayoutsCodelab() {
    val ( gesturesEnabled, toggleGesturesEnabled ) = remember { mutableStateOf( true ) }
    val scope = rememberCoroutineScope()
    val drawerState = rememberBottomDrawerState( BottomDrawerValue.Closed )

    // BottomDrawer has to be the true core of our layout
    BottomDrawer(
        gesturesEnabled = gesturesEnabled,
        drawerState = drawerState,
        drawerContent = {
            Button(
                modifier = Modifier.align( Alignment.CenterHorizontally ).padding( top = 16.dp ),
                onClick = { scope.launch { drawerState.close() } },
                content = { Text( "Close Drawer" ) }
            )
            LazyColumn {
                items( 25 ) {
                    ListItem(
                        text = { Text( "Item $it" ) },
                        icon = {
                            Icon(
                                Icons.Default.Favorite,
                                contentDescription = "Localized description"
                            )
                        }
                    )
                }
            }
        },
        // The API describes this member as "the content of the
        // rest of the UI"
        content = {
            // So let's place the Scaffold here
            Scaffold(
                topBar = {
                    AppBarContent()
                },
                //drawerContent = { BottomBar() }  // <-- Will implement a side drawer
                bottomBar = {
                    BottomBarContent(
                        coroutineScope = scope,
                        drawerState = drawerState
                    )
                            },
            ) {
                innerPadding ->
                BodyContent( Modifier.padding( innerPadding ).fillMaxHeight() )
            }
        }
    )
}

Here, we've leveraged the Scaffold exactly as the codelab in the compose pathway suggests we should. Notice my comment that drawerContent is an auto-implementation of the side-drawer. It's a rather nifty way to bypass directly using the [respective] Composable(s) (material design's modal drawer/sheet)! However, it won't work for our BottomDrawer. I think the API is experimental for BottomDrawer, because they'll be making changes to add support for it to Composables like Scaffold in the future.

I base that on how difficult it is to use the BottomDrawer, designed for use solely with BottomAppBar, with the Scaffold - which explicitly contains a slot for BottomAppBar.

To support BottomDrawer, we have to understand that it is an underlying layout controller that wraps the entire app's UI, preventing interaction with anything but its drawerContent when the drawer is open. This requires that it encompasses Scaffold, and that requires that we delegate necessary state control - to the BottomBarContent composable which wraps our BottomAppBar implementation:

@ExperimentalMaterialApi
@Composable
fun BottomBarContent( modifier: Modifier = Modifier, coroutineScope: CoroutineScope, drawerState: BottomDrawerState   ) {
    BottomAppBar{
        // Leading icons should typically have a high content alpha
        CompositionLocalProvider( LocalContentAlpha provides ContentAlpha.high ) {
            IconButton(
                onClick = {
                    coroutineScope.launch { drawerState.open() }
                }
            ) {
                Icon( Icons.Filled.Menu, contentDescription = "Localized description" )
            }
        }
        // The actions should be at the end of the BottomAppBar. They use the default medium
        // content alpha provided by BottomAppBar
        Spacer( Modifier.weight( 1f, true ) )
        IconButton( onClick = { /* doSomething() */ } ) {
            Icon( Icons.Filled.Favorite, contentDescription = "Localized description" )
        }
        IconButton( onClick = { /* doSomething() */ } ) {
            Icon( Icons.Filled.Favorite, contentDescription = "Localized description" )
        }
    }
}

The result shows us:

• The TopAppBar at top,
• The BottomAppBar at bottom,
• Clicking the menu icon in the BottomAppBar opens our BottomDrawer, covering the BottomAppBar and entire content space appropriately while open.
• The BottomDrawer is properly hidden, until either the above referenced button click - or gesture - is utilized to open the bottom drawer.
• The menu icon in the BottomAppBar opens the drawer partway.
• Gesture opens the bottom drawer partway with a quick short swipe, but as far as you guide it to otherwise.

Answer 2

You may have to do something as shown below.. Notice how the Scaffold is called inside the BottomDrawer(). It's confusing though how the documentation says "They (BottomDrawer) are only used with bottom app bars". It made me think I have to look for a BottomDrawer() slot inside Scaffold or that I have to call BottomDrawer() inside BottomAppBar(). In both cases, I experienced weird behaviours. This is how I worked around the issue. I hope it helps someone especially if you are attempting the code lab exercise in Module 5 of Layouts in Jetpack Compose from the Jetpack Compose course.

@ExperimentalMaterialApi
    @Composable
    fun MyApp() {
           var selectedItem by rememberSaveable { mutableStateOf(1)}

    BottomDrawer(
        modifier = Modifier.background(MaterialTheme.colors.onPrimary),
        drawerShape = Shapes.medium,
        drawerContent = {
            Column(Modifier.fillMaxWidth()) {
        for(i in 1..6) {
            when (i) {
                1 -> Row(modifier = Modifier.clickable {  }.padding(16.dp)){
                    Icon(imageVector = Icons.Rounded.Inbox, contentDescription = null)
                    Text(text = "Inbox")
                }
                2 -> Row(modifier = Modifier.clickable {  }.padding(16.dp)){
                    Icon(imageVector = Icons.Rounded.Outbox, contentDescription = null)
                    Text(text = "Outbox")
                }
                3 -> Row(modifier = Modifier.clickable {  }.padding(16.dp)){
                    Icon(imageVector = Icons.Rounded.Archive, contentDescription = null)
                    Text(text = "Archive")
                }
            }
        }
    }
        },
        gesturesEnabled = true
    ) {
        Scaffold(
            topBar = {
                TopAppBar(
                    title = {
                        Text(text = "Learning Compose Layouts" )
                    },
                    actions = {
                        IconButton(onClick = { /*TODO*/ }) {
                            Icon(Icons.Filled.Favorite, contentDescription = null)
                        }
                    }
                )
            },
            bottomBar = { BottomAppBar(cutoutShape = CircleShape, contentPadding = PaddingValues(0.dp)) {
                for (item in 1..4) {
                    BottomNavigationItem(
                        modifier = Modifier.clipToBounds(),
                        selected = selectedItem == item ,
                        onClick = { selectedItem = item },
                        icon = {
                            when (item) {
                                1 -> { Icon(Icons.Rounded.MusicNote, contentDescription = null) }
                                2 -> { Icon(Icons.Rounded.BookmarkAdd, contentDescription = null) }
                                3 -> { Icon(Icons.Rounded.SportsBasketball, contentDescription = null) }
                                4 -> { Icon(Icons.Rounded.ShoppingCart, contentDescription = null) }
                            }
                        }
                    )
                }
            } 
         }
      ) { innerPadding -> BodyContent(
                    Modifier
                    .padding(innerPadding)
                    .padding(8.dp))
        }
    }
}

Answer 3

I think the latest version of scaffold does have a bottom app bar parameter