Navigation Architecture

Overview

Divvy uses Jetpack Compose Navigation with Kotlin serialization for type-safe navigation. This approach eliminates string-based routes and provides compile-time safety for navigation arguments. All app destinations are defined as a sealed interface with serializable data classes:

app/src/main/java/com/example/divvy/ui/navigation/AppDestination.kt

@Serializable
sealed interface AppDestination {

    @Serializable data object Home      : AppDestination
    @Serializable data object Groups    : AppDestination
    @Serializable data object Friends   : AppDestination
    @Serializable data object Ledger    : AppDestination
    @Serializable data object Analytics : AppDestination
    @Serializable data object Profile   : AppDestination

    @Serializable
    data class GroupDetail(val groupId: String) : AppDestination

    @Serializable
    data object ScanReceipt : AppDestination

    @Serializable
    data class SplitExpense(
        val scannedAmount: String = "",
        val scannedDescription: String = "",
        val preselectedGroupId: String = ""
    ) : AppDestination

    @Serializable
    data class AssignItems(
        val groupId: String,
        val amountDisplay: String,
        val description: String
    ) : AppDestination

    @Serializable
    data class SplitByPercentage(
        val groupId: String,
        val amountDisplay: String,
        val description: String
    ) : AppDestination
}

Type Safety: Using @Serializable data classes ensures navigation arguments are type-safe and validated at compile time.

Main Tabs

Home - Activity feed and quick actions
Groups - Manage expense groups
Friends - Friend connections
Profile - User account settings

Feature Flows

GroupDetail - View group expenses and members
ScanReceipt - Camera-based receipt scanning
SplitExpense - Choose split method
AssignItems - Item-level expense assignment
SplitByPercentage - Percentage-based splits

Secondary Screens

Ledger - All balances and settlements
Analytics - Spending insights

The AppNavHost defines the navigation graph with all composable destinations:

app/src/main/java/com/example/divvy/ui/navigation/AppNavHost.kt

@Composable
fun AppNavHost(
    navController: NavHostController,
    modifier: Modifier = Modifier
) {
    NavHost(
        navController = navController,
        startDestination = AppDestination.Home,
        modifier = modifier
    ) {
        composable<AppDestination.Home> {
            HomeScreen(
                onGroupClick = { id -> 
                    navController.navigate(AppDestination.GroupDetail(id)) 
                },
                onGroupsClick = {
                    navController.navigate(AppDestination.Groups) {
                        popUpTo(navController.graph.findStartDestination().id) { 
                            saveState = true 
                        }
                        launchSingleTop = true
                        restoreState = true
                    }
                },
                onAddExpense = { 
                    navController.navigate(AppDestination.SplitExpense()) 
                },
                onLedgerClick = { 
                    navController.navigate(AppDestination.Ledger) 
                }
            )
        }
        
        composable<AppDestination.Groups> {
            GroupsScreen(
                onGroupClick = { id -> 
                    navController.navigate(AppDestination.GroupDetail(id)) 
                },
                onCreatedGroupNavigate = { id ->
                    navController.navigate(AppDestination.GroupDetail(id))
                }
            )
        }
        
        composable<AppDestination.GroupDetail> { backStack ->
            val dest: AppDestination.GroupDetail = backStack.toRoute()
            GroupDetailScreen(
                groupId = dest.groupId,
                onBack = { navController.popBackStack() },
                onLeaveGroup = {
                    navController.popBackStack(
                        route = AppDestination.Home,
                        inclusive = false
                    )
                },
                onAddExpense = {
                    navController.navigate(
                        AppDestination.SplitExpense(
                            preselectedGroupId = dest.groupId
                        )
                    )
                }
            )
        }
        
        composable<AppDestination.ScanReceipt> {
            ScanReceiptScreen(
                onBack = { navController.popBackStack() },
                onScanComplete = { amount, description ->
                    navController.popBackStack()
                    navController.navigate(
                        AppDestination.SplitExpense(
                            scannedAmount = amount,
                            scannedDescription = description
                        )
                    )
                }
            )
        }
        
        composable<AppDestination.SplitExpense> {
            SplitExpenseScreen(
                onBack = { navController.popBackStack() },
                onNavigateToAssignItems = { groupId, amount, description ->
                    navController.navigate(
                        AppDestination.AssignItems(groupId, amount, description)
                    )
                },
                onNavigateToSplitByPercentage = { groupId, amount, description ->
                    navController.navigate(
                        AppDestination.SplitByPercentage(groupId, amount, description)
                    )
                }
            )
        }
    }
}

Passing Arguments

Navigation arguments are passed as constructor parameters:

Simple Navigation
Multiple Arguments
Optional Arguments

// Navigate with multiple parameters
navController.navigate(
    AppDestination.AssignItems(
        groupId = "abc123",
        amountDisplay = "$42.50",
        description = "Dinner at Pizza Palace"
    )
)

// Optional parameters with defaults
navController.navigate(
    AppDestination.SplitExpense(
        scannedAmount = "25.00",
        scannedDescription = "Groceries"
        // preselectedGroupId uses default empty string
    )
)

Retrieving Arguments

Arguments are retrieved using toRoute() extension function:

composable<AppDestination.GroupDetail> { backStack ->
    val dest: AppDestination.GroupDetail = backStack.toRoute()
    GroupDetailScreen(
        groupId = dest.groupId,  // Type-safe access
        onBack = { navController.popBackStack() }
    )
}

ViewModel Factory with Arguments

For ViewModels that need navigation arguments, use Hilt’s assisted injection:

app/src/main/java/com/example/divvy/ui/navigation/AppNavHost.kt

composable<AppDestination.SplitByPercentage> { backStack ->
    val dest: AppDestination.SplitByPercentage = backStack.toRoute()
    val viewModel = hiltViewModel<
        SplitByPercentageViewModel, 
        SplitByPercentageViewModel.Factory
    >(
        creationCallback = { factory ->
            factory.create(
                dest.groupId, 
                dest.amountDisplay, 
                dest.description
            )
        }
    )
    SplitByPercentageScreen(
        viewModel = viewModel,
        onBack = { navController.popBackStack() },
        onDone = {
            navController.popBackStack(
                route = AppDestination.Home,
                inclusive = false
            )
        }
    )
}

The ViewModel factory pattern allows Hilt to inject dependencies while accepting navigation arguments.

The bottom navigation bar provides quick access to main tabs:

app/src/main/java/com/example/divvy/ui/navigation/BottomNavigationBar.kt

@Composable
fun BottomNavigationBar(navController: NavController) {
    val navBackStackEntry by navController.currentBackStackEntryAsState()
    val currentDestination = navBackStackEntry?.destination

    Box(
        modifier = Modifier.fillMaxWidth().height(80.dp),
        contentAlignment = Alignment.BottomCenter
    ) {
        Row(
            modifier = Modifier
                .fillMaxWidth()
                .height(64.dp)
                .background(MaterialTheme.colorScheme.surface),
            horizontalArrangement = Arrangement.SpaceAround
        ) {
            NavItem(
                icon = Icons.Rounded.Home,
                label = "Home",
                isSelected = currentDestination?.hasRoute<AppDestination.Home>() == true,
                onClick = {
                    navController.navigate(AppDestination.Home) {
                        popUpTo(navController.graph.findStartDestination().id) { 
                            saveState = true 
                        }
                        launchSingleTop = true
                        restoreState = true
                    }
                }
            )
            
            NavItem(
                icon = Icons.Rounded.Group,
                label = "Groups",
                isSelected = currentDestination?.hasRoute<AppDestination.Groups>() == true,
                onClick = {
                    navController.navigate(AppDestination.Groups) {
                        popUpTo(navController.graph.findStartDestination().id) { 
                            saveState = true 
                        }
                        launchSingleTop = true
                        restoreState = true
                    }
                }
            )
            
            Spacer(modifier = Modifier.size(48.dp)) // Space for FAB
            
            NavItem(
                icon = Icons.Rounded.People,
                label = "Friends",
                isSelected = currentDestination?.hasRoute<AppDestination.Friends>() == true,
                onClick = { /* ... */ }
            )
            
            NavItem(
                icon = Icons.Rounded.Person,
                label = "Account",
                isSelected = currentDestination?.hasRoute<AppDestination.Profile>() == true,
                onClick = { /* ... */ }
            )
        }
        
        // Center FAB for receipt scanning
        Box(
            modifier = Modifier
                .align(Alignment.TopCenter)
                .offset(y = (-20).dp)
                .size(56.dp)
                .clip(CircleShape)
                .background(MaterialTheme.colorScheme.primary)
                .clickable { navController.navigate(AppDestination.ScanReceipt) },
            contentAlignment = Alignment.Center
        ) {
            Icon(
                imageVector = Icons.Default.CameraAlt,
                contentDescription = "Scan Receipt"
            )
        }
    }
}

Save State
Launch Single Top
Restore State

popUpTo(navController.graph.findStartDestination().id) { 
    saveState = true 
}

Preserves the state when navigating away from a tab

launchSingleTop = true

Prevents multiple instances of the same destination

restoreState = true

Restores saved state when returning to a tab

Deep Linking

Divvy supports deep linking for group invitations through Supabase Auth:

Auth Redirect Configuration

app/src/main/java/com/example/divvy/di/NetworkModule.kt

install(Auth) {
    scheme = "com.example.divvy"
    host = "auth"
    defaultExternalAuthAction = ExternalAuthAction.CUSTOM_TABS
}

Redirect URL Pattern

com.example.divvy://auth

This URL must be configured in Supabase Auth settings to enable:

Google OAuth sign-in redirects
Group invitation deep links
Password reset flows

Ensure the redirect URL is added to your Supabase project’s Auth settings under “Redirect URLs”.

AndroidManifest Configuration

<activity android:name=".MainActivity">
    <intent-filter>
        <action android:name="android.intent.action.VIEW" />
        <category android:name="android.intent.category.DEFAULT" />
        <category android:name="android.intent.category.BROWSABLE" />
        <data
            android:scheme="com.example.divvy"
            android:host="auth" />
    </intent-filter>
</activity>

Creating an Expense

Group Management

Back Stack Management

Pop to Destination

// Return to Home after completing expense
navController.popBackStack(
    route = AppDestination.Home,
    inclusive = false  // Keep Home in the stack
)

Pop Current Screen

// Simple back navigation
navController.popBackStack()

Clear Back Stack

// Navigate to Home and clear everything else
navController.navigate(AppDestination.Home) {
    popUpTo(0) { inclusive = true }
    launchSingleTop = true
}

@Test
fun navigateToGroupDetail_displaysGroupId() {
    val navController = TestNavHostController(context)
    navController.setGraph(R.navigation.app_nav_graph)
    
    composeTestRule.setContent {
        AppNavHost(navController = navController)
    }
    
    // Navigate to group detail
    navController.navigate(AppDestination.GroupDetail("group123"))
    
    // Verify navigation
    assertEquals(
        AppDestination.GroupDetail("group123"),
        navController.currentBackStackEntry?.toRoute()
    )
}

Best Practices

Use Type-Safe Routes

Always use AppDestination sealed interface instead of string routes

Validate Arguments

Use non-nullable types for required arguments, nullable types for optional ones

Handle Back Navigation

Always provide onBack callbacks in screen composables

Save Tab State

Use saveState and restoreState for bottom navigation tabs

Avoid Deep Stacks

Pop back to main screens after completing flows (like expense creation)

Don’t pass complex objects through navigation. Use IDs and fetch data in ViewModels using repositories.

Common Patterns

LaunchedEffect(uiState.createCompletedGroupId) {
    val groupId = uiState.createCompletedGroupId ?: return@LaunchedEffect
    onCreatedGroupNavigate(groupId)
    viewModel.onCreateNavigationHandled()
}

Multi-Step Flows

// Step 1: Split Expense
SplitExpenseScreen(
    onNavigateToAssignItems = { groupId, amount, description ->
        navController.navigate(
            AppDestination.AssignItems(groupId, amount, description)
        )
    }
)

// Step 2: Assign Items
AssignItemsScreen(
    onDone = {
        navController.popBackStack(
            route = AppDestination.Home,
            inclusive = false
        )
    }
)

Architecture

Data Models

Repositories

Contributing

Navigation Architecture

Overview

Navigation Destinations

Navigation Routes

Main Tabs

Feature Flows

Secondary Screens

Navigation Graph

Navigation with Arguments

Passing Arguments

Retrieving Arguments

ViewModel Factory with Arguments

Bottom Navigation

Navigation Options for Tabs

Deep Linking

Auth Redirect Configuration

Redirect URL Pattern

AndroidManifest Configuration

Navigation Flow Examples

Creating an Expense

Group Management

Back Stack Management

Pop to Destination

Pop Current Screen

Clear Back Stack

Testing Navigation

Navigation Testing Example

Best Practices

Common Patterns

Conditional Navigation

Multi-Step Flows

Next Steps

MVVM Pattern

Architecture Overview

Architecture

Data Models

Repositories

Contributing

​Overview

​Navigation Destinations

​Navigation Routes

Main Tabs

Feature Flows

Secondary Screens

​Navigation Graph

​Navigation with Arguments

​Passing Arguments

​Retrieving Arguments

​ViewModel Factory with Arguments

​Bottom Navigation

​Navigation Options for Tabs

​Deep Linking

​Auth Redirect Configuration

​Redirect URL Pattern

​AndroidManifest Configuration

​Navigation Flow Examples

​Creating an Expense

​Group Management

​Back Stack Management

​Pop to Destination

​Pop Current Screen

​Clear Back Stack

​Testing Navigation

​Navigation Testing Example

​Best Practices

​Common Patterns

​Conditional Navigation

​Multi-Step Flows

​Next Steps

MVVM Pattern

Architecture Overview

Overview

Navigation Destinations

Navigation Routes

Navigation Graph

Navigation with Arguments

Passing Arguments

Retrieving Arguments

ViewModel Factory with Arguments

Bottom Navigation

Navigation Options for Tabs

Deep Linking

Auth Redirect Configuration

Redirect URL Pattern

AndroidManifest Configuration

Navigation Flow Examples

Creating an Expense

Group Management

Back Stack Management

Pop to Destination

Pop Current Screen

Clear Back Stack

Testing Navigation

Navigation Testing Example

Best Practices

Common Patterns

Conditional Navigation

Multi-Step Flows

Next Steps