Conditional Navigation Recipe

This recipe demonstrates how to implement conditional navigation, where certain destinations are only accessible if a condition is met (in this case, if the user is logged in).

How it works

This example has a Profile destination that requires the user to be logged in. If the user is not logged in and attempts to navigate to Profile, they are redirected to a Login screen. After a successful login, they are automatically navigated to the Profile screen.

AppBackStack

The core of this recipe is the custom AppBackStack class, which encapsulates the logic for conditional navigation.

  • RequiresLogin interface: A marker interface, RequiresLogin, is used to identify destinations that require the user to be logged in. The Profile destination implements this interface.

  • Redirecting to Login: When the add function is called with a destination that implements RequiresLogin and the user is not logged in, AppBackStack stores the intended destination and adds the Login route to the back stack instead.

  • Handling Login: When the login function is called, it sets the user's status to logged in. If there is a stored destination that the user was trying to access, it adds that destination to the back stack and removes the Login screen.

  • Handling Logout: When the logout function is called, it sets the user's status to logged out and removes any destinations from the back stack that require the user to be logged in.

This approach provides a clean way to handle conditional navigation by centralizing the logic in a custom back stack implementation.

/*
 * 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.conditional

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.layout.Column
import androidx.compose.material3.Button
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.setValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.saveable.rememberSaveable
import androidx.compose.runtime.saveable.rememberSerializable
import androidx.lifecycle.compose.dropUnlessResumed
import androidx.navigation3.runtime.NavBackStack
import androidx.navigation3.runtime.NavKey
import androidx.navigation3.runtime.entryProvider
import androidx.navigation3.runtime.serialization.NavBackStackSerializer
import androidx.navigation3.runtime.serialization.NavKeySerializer
import androidx.navigation3.ui.NavDisplay
import com.example.nav3recipes.content.ContentBlue
import com.example.nav3recipes.content.ContentGreen
import com.example.nav3recipes.content.ContentYellow
import kotlinx.serialization.Serializable


/**
 * Class for representing navigation keys in the app.
 *
 * Note: We use a sealed class because KotlinX Serialization handles
 * polymorphic serialization of sealed classes automatically.
 *
 * @param requiresLogin - true if the navigation key requires that the user is logged in
 * to navigate to it
 */
@Serializable
sealed class ConditionalNavKey(val requiresLogin: Boolean = false) : NavKey

/**
 * Key representing home screen
 */
@Serializable
private data object Home : ConditionalNavKey()

/**
 * Key representing profile screen that is only accessible once the user has logged in
 */
@Serializable
private data object Profile : ConditionalNavKey(requiresLogin = true)

/**
 * Key representing login screen
 *
 * @param redirectToKey - navigation key to redirect to after successful login
 */
@Serializable
private data class Login(
    val redirectToKey: ConditionalNavKey? = null
) : ConditionalNavKey()

class ConditionalActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {

            val backStack = rememberNavBackStack<ConditionalNavKey>(Home)
            var isLoggedIn by rememberSaveable {
                mutableStateOf(false)
            }
            val navigator = remember {
                Navigator(
                    backStack = backStack,
                    onNavigateToRestrictedKey = { redirectToKey -> Login(redirectToKey) },
                    isLoggedIn = { isLoggedIn }
                )
            }

            NavDisplay(
                backStack = backStack,
                onBack = { navigator.goBack() },
                entryProvider = entryProvider {
                    entry<Home> {
                        ContentGreen("Welcome to Nav3. Logged in? ${isLoggedIn}") {
                            Column {
                                Button(onClick = dropUnlessResumed { navigator.navigate(Profile) }) {
                                    Text("Profile")
                                }
                                Button(onClick = dropUnlessResumed { navigator.navigate(Login()) }) {
                                    Text("Login")
                                }
                            }
                        }
                    }
                    entry<Profile> {
                        ContentBlue("Profile screen (only accessible once logged in)") {
                            Button(onClick = dropUnlessResumed {
                                isLoggedIn = false
                                navigator.navigate(Home)
                            }) {
                                Text("Logout")
                            }
                        }
                    }
                    entry<Login> { key ->
                        ContentYellow("Login screen. Logged in? $isLoggedIn") {
                            Button(onClick = dropUnlessResumed {
                                isLoggedIn = true
                                key.redirectToKey?.let { targetKey ->
                                    backStack.remove(key)
                                    navigator.navigate(targetKey)
                                }
                            }) {
                                Text("Login")
                            }
                        }
                    }
                }
            )
        }
    }
}


// An overload of `rememberNavBackStack` that returns a subtype of `NavKey`.
// See https://issuetracker.google.com/issues/463382671 for a discussion of this function
@Composable
fun <T : NavKey> rememberNavBackStack(vararg elements: T): NavBackStack<T> {
    return rememberSerializable(
        serializer = NavBackStackSerializer(elementSerializer = NavKeySerializer())
    ) {
        NavBackStack(*elements)
    }
}
ConditionalActivity.kt
 
/*
 * 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.conditional

import androidx.navigation3.runtime.NavBackStack

/**
 * Provides navigation events with built-in support for conditional access. If the user attempts to
 * navigate to a [ConditionalNavKey] that requires login ([ConditionalNavKey.requiresLogin] is true)
 * but is not currently logged in, the Navigator will redirect the user to a login key.
 *
 * @property backStack The back stack that is modified by this class
 * @property onNavigateToRestrictedKey A lambda that is called when the user attempts to navigate
 * to a key that requires login. This should return the key that represents the login screen. The
 * user's target key is supplied as a parameter so that after successful login the user can be
 * redirected to their target destination.
 * @property isLoggedIn A lambda that returns whether the user is logged in.
 */
class Navigator(
    private val backStack: NavBackStack<ConditionalNavKey>,
    private val onNavigateToRestrictedKey: (targetKey: ConditionalNavKey?) -> ConditionalNavKey,
    private val isLoggedIn: () -> Boolean,
) {
    fun navigate(key: ConditionalNavKey) {
        if (key.requiresLogin && !isLoggedIn()) {
            val loginKey = onNavigateToRestrictedKey(key)
            backStack.add(loginKey)
        } else {
            backStack.add(key)
        }
    }

    fun goBack() = backStack.removeLastOrNull()
}
Navigator.kt