Nested navigation graphs in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a NavHostFragment in the activity layout.

Android Kotlin

val navHostFragment = supportFragmentManager.findFragmentById(R.id.[1]) as NavHostFragment

Drag options to blanks, or click blank then click option'

Anav_host_fragment

Bmain_nav_host

Cnav_graph_host

Dfragment_container

Attempts:

3 left

💡 Hint

Common Mistakes

Using an incorrect fragment ID that does not exist in the layout.

Confusing the NavHostFragment ID with other container IDs.

The NavHostFragment is usually referenced by its ID in the layout, commonly named 'nav_host_fragment'.

2fill in blank

medium

Complete the code to navigate to a nested graph destination using NavController.

Android Kotlin

navController.navigate(R.id.[1])

Drag options to blanks, or click blank then click option'

AprofileFragment

BhomeFragment

Cnested_graph

DsettingsFragment

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to navigate directly to a fragment inside the nested graph without specifying the nested graph ID.

Using a fragment ID instead of the nested graph ID.

To navigate to a nested navigation graph, you use the ID of the nested graph itself, not a fragment destination.

3fill in blank

hard

Fix the error in the nested graph XML by completing the missing attribute.

Android Kotlin

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/[1]"
    app:startDestination="homeFragment">

Drag options to blanks, or click blank then click option'

Amain_graph

Bapp_nav_graph

Croot_graph

Dnested_graph

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same ID as the main graph causing conflicts.

Omitting the android:id attribute entirely.

The nested graph must have a unique ID, commonly named 'nested_graph' to distinguish it from the main graph.

4fill in blank

hard

Fill both blanks to define a nested navigation graph with a start destination.

Android Kotlin

<navigation android:id="@+id/[1]" app:startDestination="[2]">

Drag options to blanks, or click blank then click option'

Anested_graph

BhomeFragment

CprofileFragment

Dmain_graph

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the graph ID with fragment IDs.

Setting a start destination that does not exist in the nested graph.

The nested graph ID is 'nested_graph' and its start destination is 'homeFragment'.

5fill in blank

hard

Fill all three blanks to correctly retrieve the NavController from a nested NavHostFragment.

Android Kotlin

val navHostFragment = supportFragmentManager.findFragmentById(R.id.[1]) as [2]
val navController = navHostFragment.[3]

Drag options to blanks, or click blank then click option'

Anested_nav_host

BNavHostFragment

CnavController

Dmain_nav_host

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong fragment ID.

Casting to the wrong fragment type.

Trying to access navController without casting.

You find the nested NavHostFragment by its ID 'nested_nav_host', cast it to NavHostFragment, then get its navController property.

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