# Bottom Sheet Recipe

This recipe demonstrates how to display a destination as a modal bottom sheet.

## How it works

To show a destination as a bottom sheet, you need to do two things:

1. **Use `BottomSheetSceneStrategy`** : Create an instance of `BottomSheetSceneStrategy` and pass it to the `sceneStrategy` parameter of the `NavDisplay` composable.

2. **Add metadata to the destination** : For the destination that you want to display as a bottom sheet, add `BottomSheetSceneStrategy.bottomSheet()` to its metadata. This is done in the `entry` function.

In this example, `RouteB` is configured to be a bottom sheet. When you navigate from `RouteA` to `RouteB`, `RouteB` will be displayed in a modal bottom sheet that slides up from the bottom of the screen.

The content of the bottom sheet can be styled as needed. In this recipe, the content is clipped to have rounded corners.

For more information, see the official documentation on [custom layouts](https://developer.android.com/guide/navigation/navigation-3/custom-layouts).  

```python
/*
 * Copyright 2025 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.nav3recipes.bottomsheet

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.material3.Button
import androidx.compose.material3.ExperimentalMaterial3Api
import androidx.compose.material3.Text
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.unit.dp
import androidx.navigation3.runtime.NavKey
import androidx.navigation3.runtime.entryProvider
import androidx.navigation3.runtime.rememberNavBackStack
import androidx.navigation3.ui.NavDisplay
import com.example.nav3recipes.content.ContentBlue
import com.example.nav3recipes.content.ContentGreen
import com.example.nav3recipes.ui.setEdgeToEdgeConfig
import kotlinx.serialization.Serializable

@Serializable
private data object RouteA : NavKey

@Serializable
private data class RouteB(val id: String) : NavKey

class BottomSheetActivity : ComponentActivity() {

    @OptIn(ExperimentalMaterial3Api::class)
    override fun onCreate(savedInstanceState: Bundle?) {
        setEdgeToEdgeConfig()
        super.onCreate(savedInstanceState)
        setContent {
            val backStack = rememberNavBackStack(RouteA)
            val bottomSheetStrategy = remember { BottomSheetSceneStrategy<NavKey>() }

            NavDisplay(
                backStack = backStack,
                onBack = { backStack.removeLastOrNull() },
                sceneStrategy = bottomSheetStrategy,
                entryProvider = entryProvider {
                    entry<RouteA> {
                        ContentGreen("Welcome to Nav3") {
                            Button(onClick = {
                                backStack.add(RouteB("123"))
                            }) {
                                Text("Click to open bottom sheet")
                            }
                        }
                    }
                    entry<RouteB>(
                        metadata = BottomSheetSceneStrategy.bottomSheet()
                    ) { key ->
                        ContentBlue(
                            title = "Route id: ${key.id}",
                            modifier = Modifier.clip(
                                shape = RoundedCornerShape(16.dp)
                            )
                        )
                    }
                }
            )
        }
    }
}
```  

```python
package com.example.nav3recipes.bottomsheet

import androidx.compose.material3.ExperimentalMaterial3Api
import androidx.compose.material3.ModalBottomSheet
import androidx.compose.material3.ModalBottomSheetProperties
import androidx.compose.runtime.Composable
import androidx.navigation3.runtime.NavEntry
import androidx.navigation3.scene.OverlayScene
import androidx.navigation3.scene.Scene
import androidx.navigation3.scene.SceneStrategy
import androidx.navigation3.scene.SceneStrategyScope

/** An [OverlayScene] that renders an [entry] within a [ModalBottomSheet]. */
@OptIn(ExperimentalMaterial3Api::class)
internal class BottomSheetScene<T : Any>(
    override val key: T,
    override val previousEntries: List<NavEntry<T>>,
    override val overlaidEntries: List<NavEntry<T>>,
    private val entry: NavEntry<T>,
    private val modalBottomSheetProperties: ModalBottomSheetProperties,
    private val onBack: () -> Unit,
) : OverlayScene<T> {

    override val entries: List<NavEntry<T>> = listOf(entry)

    override val content: @Composable (() -> Unit) = {
        ModalBottomSheet(
            onDismissRequest = onBack,
            properties = modalBottomSheetProperties,
        ) {
            entry.Content()
        }
    }
}

/**
 * A [SceneStrategy] that displays entries that have added [bottomSheet] to their [NavEntry.metadata]
 * within a [ModalBottomSheet] instance.
 *
 * This strategy should always be added before any non-overlay scene strategies.
 */
@OptIn(ExperimentalMaterial3Api::class)
class BottomSheetSceneStrategy<T : Any> : SceneStrategy<T> {

    override fun SceneStrategyScope<T>.calculateScene(entries: List<NavEntry<T>>): Scene<T>? {
        val lastEntry = entries.lastOrNull()
        val bottomSheetProperties = lastEntry?.metadata?.get(BOTTOM_SHEET_KEY) as? ModalBottomSheetProperties
        return bottomSheetProperties?.let { properties ->
            @Suppress("UNCHECKED_CAST")
            BottomSheetScene(
                key = lastEntry.contentKey as T,
                previousEntries = entries.dropLast(1),
                overlaidEntries = entries.dropLast(1),
                entry = lastEntry,
                modalBottomSheetProperties = properties,
                onBack = onBack
            )
        }
    }

    companion object {
        /**
         * Function to be called on the [NavEntry.metadata] to mark this entry as something that
         * should be displayed within a [ModalBottomSheet].
         *
         * @param modalBottomSheetProperties properties that should be passed to the containing
         * [ModalBottomSheet].
         */
        @OptIn(ExperimentalMaterial3Api::class)
        fun bottomSheet(
            modalBottomSheetProperties: ModalBottomSheetProperties = ModalBottomSheetProperties()
        ): Map<String, Any> = mapOf(BOTTOM_SHEET_KEY to modalBottomSheetProperties)

        internal const val BOTTOM_SHEET_KEY = "bottomsheet"
    }
}
```