Passing arguments in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Passing arguments between Android fragments

You want to pass a string argument from FragmentA to FragmentB using a Bundle. Which code snippet correctly sets the argument in FragmentA before navigation?

Android Kotlin

val bundle = Bundle()
bundle.putString("userName", "Alice")
val fragmentB = FragmentB()
fragmentB.arguments = bundle
// Navigate to fragmentB

A

val bundle = Bundle()
bundle.putString("userName")
val fragmentB = FragmentB()
fragmentB.arguments = bundle

B

val fragmentB = FragmentB()
fragmentB.arguments?.putString("userName", "Alice")

C

val bundle = Bundle()
bundle.putInt("userName", 123)
val fragmentB = FragmentB()
fragmentB.arguments = bundle

D

val bundle = Bundle()
bundle.putString("userName", "Alice")
val fragmentB = FragmentB()
fragmentB.arguments = bundle

💡 Hint

Remember to use putString with both key and value, and assign the bundle to the fragment's arguments.

Option D correctly creates a Bundle, puts a string with key "userName", assigns it to fragmentB.arguments. Option D uses putInt with a string key which is incorrect for a string value. Option D misses the value in putString causing a syntax error. Option D tries to call putString on a null arguments property before initializing it.

📝 Syntax

intermediate

Correct syntax for passing arguments in Kotlin function

Which option shows the correct way to define a Kotlin function that takes a string argument and prints it?

Android Kotlin

fun greet(name: String) {
    println("Hello, $name")
}

A

fun greet(name) {
    println("Hello, $name")
}

B

fun greet(name: String) {
    println("Hello, $name")
}

C

fun greet(name: String) -> Unit {
    println("Hello, $name")
}

D

fun greet(String name) {
    println("Hello, $name")
}

💡 Hint

In Kotlin, parameter types come after the name separated by a colon.

Option B uses correct Kotlin syntax: parameter name followed by colon and type. Option B misses the type causing a syntax error. Option B uses incorrect arrow syntax for function body. Option B uses Java-like syntax which is invalid in Kotlin.

❓ lifecycle

advanced

Accessing passed arguments in Fragment lifecycle

Where is the best place to safely retrieve arguments passed to a Fragment in Android?

A Inside the onCreate() method using requireArguments()

B Inside the onCreateView() method using getArguments() without null check

C Inside the onAttach() method using arguments!!

D Inside the onDestroyView() method using arguments

💡 Hint

Arguments are available early in the fragment lifecycle but before view creation.

Option A is correct because onCreate() is called early and requireArguments() safely returns the Bundle or throws if missing. Option A risks null pointer without null check. Option A is too early and unsafe to use !! operator. Option A is too late as view is destroyed.

❓ navigation

advanced

Passing arguments using Safe Args in Navigation Component

Using Android Navigation Component with Safe Args, how do you pass an integer argument named userId from FragmentA to FragmentB?

A

val action = FragmentBDirections.actionFragmentBToFragmentA(userId = 42)
findNavController().navigate(action)

B

val bundle = Bundle()
bundle.putInt("userId", 42)
findNavController().navigate(R.id.fragmentB, bundle)

C

val action = FragmentADirections.actionFragmentAToFragmentB(userId = 42)
findNavController().navigate(action)

D findNavController().navigate(R.id.fragmentB, bundleOf("userId" to 42))

💡 Hint

Safe Args generates directions classes with methods to pass arguments safely.

Option C uses the generated directions class from FragmentA to FragmentB with the argument userId. Option C and C use manual bundles which are valid but not Safe Args. Option C reverses the direction from FragmentB to FragmentA which is incorrect here.

🔧 Debug

expert

Why does this argument passing code crash?

Given this code in FragmentB, why does the app crash with a NullPointerException? val userName = arguments?.getString("userName")!! textView.text = userName

A Because arguments is null and the !! operator forces a crash

B Because getString("userName") returns an empty string which cannot be assigned

C Because textView is not initialized before setting text

D Because getString("userName") returns an integer, not a string

💡 Hint

Check if arguments Bundle is actually set before accessing it with !!

The code uses safe call ?. on arguments but then forces non-null with !!. If arguments is null, this causes a NullPointerException. Option A is wrong because empty string is valid. Option A could cause crash but question focuses on argument passing. Option A is wrong because getString returns String or null.