Basic Saveable Recipe

This recipe shows a basic example of how to create a persistent back stack that survives configuration changes.

How it works

To make the back stack persistent, we use the rememberNavBackStack function. This function creates and remembers the back stack across configuration changes (e.g., screen rotation).

A requirement for using rememberNavBackStack is that the navigation keys (routes) must be serializable. In this example, RouteA and RouteB are annotated with @Serializable and implement the NavKey interface.

This example uses a when statement within the entryProvider to map routes to their corresponding composables, but it could also be used with the entryProvider DSL.

/*
 * 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.basicsaveable

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.material3.Button
import androidx.compose.material3.Text
import androidx.lifecycle.compose.dropUnlessResumed
import androidx.navigation3.runtime.NavEntry
import androidx.navigation3.runtime.NavKey
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 BasicSaveableActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        setEdgeToEdgeConfig()
        super.onCreate(savedInstanceState)
        setContent {
            val backStack = rememberNavBackStack(RouteA)

            NavDisplay(
                backStack = backStack,
                onBack = { backStack.removeLastOrNull() },
                entryProvider = { key ->
                    when (key) {
                        is RouteA -> NavEntry(key) {
                            ContentGreen("Welcome to Nav3") {
                                Button(onClick = dropUnlessResumed {
                                    backStack.add(RouteB("123"))
                                }) {
                                    Text("Click to navigate")
                                }
                            }
                        }

                        is RouteB -> NavEntry(key) {
                            ContentBlue("Route id: ${key.id} ")
                        }

                        else -> {
                            error("Unknown route: $key")
                        }
                    }
                }
            )
        }
    }
}

BasicSaveableActivity.kt