Ricetta per il riquadro inferiore

/*
 * 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.lifecycle.compose.dropUnlessResumed
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 = dropUnlessResumed {
                                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)
                            )
                        )
                    }
                }
            )
        }
    }
}
BottomSheetActivity.kt

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"
    }
}
BottomSheetSceneStrategy.kt