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.

Practice

1. What is the primary purpose of passing arguments between activities in Android Kotlin?

easy

A. To close the current activity

B. To change the app theme

C. To share data between different screens

D. To update the app version

Solution

1. Step 1: Understand activity communication

   Activities often need to share information like user input or selections.

2. Step 2: Purpose of passing arguments

   Passing arguments allows one screen to send data to another screen.

3. Final Answer:

   To share data between different screens -> Option C

4. Quick Check:

   Passing arguments = sharing data [OK]

Hint: Passing arguments means sending data between screens [OK]

Common Mistakes:

• Thinking it changes app theme
• Confusing with app version updates
• Assuming it closes activities

2. Which Kotlin code correctly passes a String argument "username" with value "Alice" to another activity using Intent?

easy

A. val intent = Intent(this, NextActivity::class.java)
intent.putExtra("username", "Alice")
startActivity(intent)

B. val intent = Intent(this, NextActivity::class.java)
intent.putString("username", "Alice")
startActivity(intent)

C. val intent = Intent(this, NextActivity::class.java)
intent.addExtra("username", "Alice")
startActivity(intent)

D. val intent = Intent(this, NextActivity::class.java)
intent.setExtra("username", "Alice")
startActivity(intent)

Solution

1. Step 1: Identify correct Intent method

   The method to add data is putExtra(key, value).

2. Step 2: Check method names in options

   Only val intent = Intent(this, NextActivity::class.java) intent.putExtra("username", "Alice") startActivity(intent) uses putExtra correctly; others use invalid method names.

3. Final Answer:

   val intent = Intent(this, NextActivity::class.java)\nintent.putExtra("username", "Alice")\nstartActivity(intent) -> Option A

4. Quick Check:

   Use putExtra() to pass data [OK]

Hint: Use putExtra() to add data to Intent [OK]

Common Mistakes:

• Using non-existent methods like putString or addExtra
• Forgetting to call startActivity()
• Passing wrong argument types

3. What will be the output of the following code in the receiving activity?

val username = intent.getStringExtra("username")
textView.text = username ?: "Guest"

If the sending activity did NOT pass any "username" extra?

medium

A. The app will crash with NullPointerException

B. The TextView will show "null"

C. The TextView will be empty

D. The TextView will show "Guest"

Solution

1. Step 1: Understand getStringExtra behavior

   If no extra is passed, getStringExtra returns null.

2. Step 2: Analyze Elvis operator usage

   The expression username ?: "Guest" means if username is null, use "Guest".

3. Final Answer:

   The TextView will show "Guest" -> Option D

4. Quick Check:

   Null fallback with ?: operator = "Guest" [OK]

Hint: ?: operator provides default if null [OK]

Common Mistakes:

• Expecting null string to display
• Assuming app crashes on null
• Forgetting ?: fallback

4. Identify the error in this code snippet that tries to retrieve an Int extra named "age":

val age = intent.getIntExtra("age")
textView.text = age.toString()

medium

A. getIntExtra requires a default value as second argument

B. getIntExtra should be getIntExtras

C. age.toString() is invalid for Int

D. Intent cannot carry Int values

Solution

1. Step 1: Check getIntExtra method signature

   getIntExtra requires two arguments: key and default value.

2. Step 2: Identify missing argument

   The code misses the default value argument, causing a compile error.

3. Final Answer:

   getIntExtra requires a default value as second argument -> Option A

4. Quick Check:

   getIntExtra(key, default) needs default [OK]

Hint: Always provide default value for getIntExtra [OK]

Common Mistakes:

• Omitting default value argument
• Using wrong method name getIntExtras
• Thinking Int can't be passed

5. You want to pass a list of Strings named "items" from one activity to another. Which is the correct way to pass and retrieve this list using Intent?

hard

A. Use intent.putExtra("items", items) and intent.getStringExtra("items")

B. Use intent.putStringArrayListExtra("items", items) and intent.getStringArrayListExtra("items")

C. Use intent.putExtra("items", items.toString()) and intent.getStringExtra("items")

D. Use intent.putExtra("items", items) and intent.getSerializableExtra("items")

Solution

1. Step 1: Passing a list of Strings

   For ArrayList<String>, use putStringArrayListExtra to pass the list.

2. Step 2: Retrieving the list

   Use getStringArrayListExtra to get the list back safely.

3. Final Answer:

   Use intent.putStringArrayListExtra("items", items) and intent.getStringArrayListExtra("items") -> Option B

4. Quick Check:

   Use put/getStringArrayListExtra for String lists [OK]

Hint: Use put/getStringArrayListExtra for String lists [OK]

Common Mistakes:

• Passing list as plain putExtra
• Converting list to string incorrectly
• Using getSerializableExtra without casting