Bottom navigation bar in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Bottom Navigation Bar Item Selection Behavior

What will happen when the user taps the second item in this BottomNavigationView setup?

Android Kotlin

val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottom_navigation)
bottomNavigationView.setOnItemSelectedListener { item ->
  when(item.itemId) {
    R.id.home -> {
      showHomeFragment()
      true
    }
    R.id.search -> {
      showSearchFragment()
      true
    }
    R.id.profile -> {
      showProfileFragment()
      true
    }
    else -> false
  }
}

A The app will display the Search fragment and highlight the Search icon in the bottom bar.

B The app will display the Home fragment and highlight the Home icon in the bottom bar.

C The app will crash because the listener does not handle the second item.

D Nothing will happen because the listener returns false for the second item.

💡 Hint

Look at the itemId checked in the when block and what fragment is shown for R.id.search.

The listener checks the itemId and calls showSearchFragment() when the second item (R.id.search) is selected, returning true to indicate the event was handled. This updates the UI and highlights the Search icon.

❓ lifecycle

intermediate

State Preservation in Bottom Navigation

In an app with a BottomNavigationView switching between fragments, what is the best way to preserve each fragment's state when switching tabs?

A Use finish() on the activity when switching tabs to reset state.

B Use add() and show()/hide() methods to keep fragments alive and preserve their state.

C Create new fragment instances every time the tab is selected.

D Replace the fragment each time without adding to back stack, losing previous state.

💡 Hint

Think about how to keep fragments in memory without recreating them.

Using add() and show()/hide() keeps fragments alive in the FragmentManager, preserving their UI and data state when switching tabs.

❓ navigation

advanced

Navigation Component with Bottom Navigation Bar

Given a BottomNavigationView integrated with Navigation Component, what is the effect of calling NavigationUI.setupWithNavController(bottomNavigationView, navController)?

A It causes the app to crash if the navController is null.

B It disables the bottom navigation bar until manually enabled.

C It automatically updates the selected item in the bottom bar when navigating and handles item clicks to navigate.

D It only changes the toolbar title but does not affect navigation.

💡 Hint

Think about how NavigationUI connects UI components with navigation actions.

setupWithNavController links the BottomNavigationView with the NavController so that selecting items triggers navigation and the selected item updates automatically.

📝 Syntax

advanced

Correct Kotlin Syntax for BottomNavigationView Listener

Which option shows the correct Kotlin syntax to set a listener on BottomNavigationView that returns true when an item is selected?

A bottomNavigationView.setOnItemSelectedListener { item -> when(item.itemId) { R.id.home -> true else -> false } }

B bottomNavigationView.setOnItemSelectedListener(fun(item) { return true })

C bottomNavigationView.setOnItemSelectedListener { item -> { true } }

D bottomNavigationView.setOnItemSelectedListener { item -> if (item.itemId == R.id.home) true else false }

💡 Hint

Remember the lambda syntax and that the listener expects a Boolean return.

Option A uses a lambda with a when expression returning Boolean correctly. Option A uses invalid syntax. Option A is valid Kotlin but less idiomatic than C. Option A returns a lambda instead of Boolean.

🔧 Debug

expert

Debugging BottomNavigationView Item Highlight Issue

An app's BottomNavigationView does not highlight the selected item after tapping. Which code mistake causes this?

Android Kotlin

bottomNavigationView.setOnItemSelectedListener { item ->
  when(item.itemId) {
    R.id.home -> {
      showHomeFragment()
      false
    }
    R.id.search -> {
      showSearchFragment()
      false
    }
    else -> false
  }
}

A Not calling notifyDataSetChanged() on the BottomNavigationView adapter.

B Using showHomeFragment() instead of replaceFragment() causes UI not to update.

C Missing call to bottomNavigationView.invalidate() after selection.

D Returning false in the listener prevents the item from being highlighted as selected.

💡 Hint

Check what the listener's return value controls in BottomNavigationView.

Returning false means the event was not handled, so the BottomNavigationView does not update the selected item highlight.