Nested navigation graphs in Android Kotlin

Introduction

Nested navigation graphs help organize app screens into smaller groups. This makes your app easier to manage and navigate.

When your app has many screens and you want to group related screens together.

When you want to reuse a set of screens in different parts of your app.

When you want to separate main app flows like login, home, and settings into smaller navigation parts.

When you want to keep your navigation code clean and easier to understand.

Syntax

Android Kotlin

val navController = findNavController(R.id.nav_host_fragment)

val nestedGraph = navController.navInflater.inflate(R.navigation.nested_graph)
navController.graph.addDestination(nestedGraph)

You define nested graphs in separate XML files inside the res/navigation folder.

Use <include> tag in your main navigation XML to include nested graphs.

Examples

This is the main navigation graph. It includes a nested graph called settings_graph.

Android Kotlin

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/main_graph"
    app:startDestination="home_fragment">

    <fragment
        android:id="@+id/home_fragment"
        android:name="com.example.HomeFragment"
        android:label="Home" />

    <include app:graph="@navigation/settings_graph" />

</navigation>

This is the nested navigation graph for settings and profile screens.

Android Kotlin

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/settings_graph"
    app:startDestination="settings_fragment">

    <fragment
        android:id="@+id/settings_fragment"
        android:name="com.example.SettingsFragment"
        android:label="Settings" />

    <fragment
        android:id="@+id/profile_fragment"
        android:name="com.example.ProfileFragment"
        android:label="Profile" />

</navigation>

Sample App

This is a simple activity that hosts the navigation component. The navigation XML files define the nested graphs.

Android Kotlin

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.navigation.findNavController
import androidx.navigation.fragment.NavHostFragment

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
        val navController = navHostFragment.navController

        // The main graph includes the nested settings graph via XML
        // Navigation works seamlessly between home and settings/profile screens
    }
}

Important Notes

Nested graphs help keep navigation organized and modular.

Time complexity: Navigation actions are fast and constant time.

Common mistake: Forgetting to set the start destination in nested graphs causes navigation errors.

Use nested graphs when you want to separate flows logically, instead of putting all screens in one big graph.

Summary

Nested navigation graphs group related screens for better organization.

Use <include> in XML to add nested graphs inside main graph.

This makes your app easier to maintain and navigate.

Practice

1.

What is the main purpose of using nested navigation graphs in Android apps?

easy

A. To group related screens for better organization and easier navigation

B. To increase app size by duplicating navigation code

C. To disable navigation between screens

D. To replace fragments with activities

Solution

1. Step 1: Understand navigation graph purpose

   Navigation graphs define how screens connect and transition in an app.

2. Step 2: Role of nested graphs

   Nested graphs group related screens to keep navigation organized and maintainable.

3. Final Answer:

   To group related screens for better organization and easier navigation -> Option A

4. Quick Check:

   Nested graphs = group related screens [OK]

Hint: Nested graphs organize related screens inside main graph [OK]

Common Mistakes:

• Thinking nested graphs duplicate code
• Believing nested graphs disable navigation
• Confusing nested graphs with replacing fragments

2.

Which XML tag is used to include a nested navigation graph inside a main navigation graph?

easy

A. <graph>

B. <navigation>

C. <fragment>

D. <include>

Solution

1. Step 1: Identify tag for including nested graphs

   The <include> tag is used to insert one XML layout or graph inside another.

2. Step 2: Confirm usage in navigation graphs

   To add a nested navigation graph inside the main graph, <include> is the correct tag.

3. Final Answer:

   <include> -> Option D

4. Quick Check:

   Include tag adds nested graph [OK]

Hint: Use <include> tag to add nested graphs in XML [OK]

Common Mistakes:

• Using <graph> instead of <include>
• Confusing <fragment> with <include>
• Mistaking <navigation> as include tag

3.

Given this main navigation graph XML snippet:

<navigation xmlns:android=\"http://schemas.android.com/apk/res/android\"
    android:id=\"@+id/main_graph\"
    app:startDestination=\"@id/homeFragment\">
    <include app:graph=\"@navigation/profile_graph\" />
    <fragment android:id=\"@+id/homeFragment\" android:name=\"com.example.HomeFragment\" />
</navigation>

What happens when the app starts?

medium

A. The app starts at HomeFragment as the start destination

B. The app starts at the first fragment inside profile_graph

C. The app crashes due to missing start destination in profile_graph

D. The app shows a blank screen

Solution

1. Step 1: Check startDestination in main graph

   The main graph's startDestination is set to homeFragment explicitly.

2. Step 2: Effect of including profile_graph

   Including profile_graph adds its screens but does not change main graph's startDestination.

3. Final Answer:

   The app starts at HomeFragment as the start destination -> Option A

4. Quick Check:

   Start destination in main graph controls start [OK]

Hint: Start destination in main graph controls app start [OK]

Common Mistakes:

• Assuming nested graph startDestination overrides main
• Thinking app crashes without startDestination in nested graph
• Believing included graphs start automatically

4.

What is wrong with this nested navigation graph XML snippet?

<navigation xmlns:android=\"http://schemas.android.com/apk/res/android\"
    android:id=\"@+id/profile_graph\">
    <fragment android:id=\"@+id/profileFragment\" android:name=\"com.example.ProfileFragment\" />
</navigation>

When included in main graph, navigation to profileFragment fails. Why?

medium

A. Fragment ID is invalid with plus sign

B. Missing startDestination attribute in profile_graph

C. Fragment name is incorrect format

D. Navigation tag is missing namespace

Solution

1. Step 1: Check required attributes in navigation graph

   Every navigation graph must have a startDestination attribute to define entry point.

2. Step 2: Identify missing startDestination

   The profile_graph lacks startDestination, so navigation fails when included.

3. Final Answer:

   Missing <code>startDestination</code> attribute in profile_graph -> Option B

4. Quick Check:

   startDestination required in nested graphs [OK]

Hint: Always set startDestination in nested graphs [OK]

Common Mistakes:

• Thinking plus sign in ID causes error
• Assuming fragment name format is wrong
• Ignoring missing startDestination attribute

5.

You want to create a nested navigation graph for a settings section with two fragments: SettingsListFragment and SettingsDetailFragment. Which is the correct way to define the nested graph XML?

<navigation xmlns:android=\"http://schemas.android.com/apk/res/android\"
    android:id=\"@+id/settings_graph\"
    app:startDestination=\"@id/settingsListFragment\">
    <fragment android:id=\"@+id/settingsListFragment\" android:name=\"com.example.SettingsListFragment\" />
    <fragment android:id=\"@+id/settingsDetailFragment\" android:name=\"com.example.SettingsDetailFragment\" />
</navigation>

How should you include this nested graph inside the main navigation graph?

hard

A. Copy all fragments from settings_graph directly into main graph

B. Add <fragment android:id=\"@+id/settings_graph\" /> inside main graph

C. Use <include app:graph=\"@navigation/settings_graph\" /> inside main graph

D. Use <navigation app:graph=\"@navigation/settings_graph\" /> inside main graph

Solution

1. Step 1: Define nested graph with startDestination and fragments

   The settings_graph XML correctly defines startDestination and fragments.

2. Step 2: Include nested graph in main graph

   Use <include app:graph=\"@navigation/settings_graph\" /> to add nested graph inside main graph.

3. Final Answer:

   Use <include app:graph=\"@navigation/settings_graph\" /> inside main graph -> Option C

4. Quick Check:

   Include tag adds nested graph correctly [OK]

Hint: Include nested graph with [OK]

Common Mistakes:

• Using fragment tag instead of include
• Copying fragments instead of nesting
• Using navigation tag incorrectly inside main graph