Passing arguments in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a function that takes one argument named name.

Android Kotlin

fun greet([1]: String) {
  println("Hello, $name!")
}

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

Atext

Bmessage

Cinput

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different parameter name than 'name' causes an error because 'name' is used inside the function.

The function parameter must be named 'name' to match the usage inside the function.

2fill in blank

medium

Complete the code to call the function greet with the argument "Alice".

Android Kotlin

greet([1])

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

A"Alice"

Bname

CAlice

D'Alice'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing Alice without quotes causes a variable not found error.

Using single quotes is for characters, not strings.

String arguments in Kotlin must be enclosed in double quotes.

3fill in blank

hard

Fix the error in the function call by passing the correct argument.

Android Kotlin

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

greet([1])

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

A123

B"Bob"

Ctrue

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a number or boolean instead of a string causes a type mismatch error.

The function expects a String argument, so we must pass a string like "Bob".

4fill in blank

hard

Fill both blanks to define a function with two parameters and call it correctly.

Android Kotlin

fun greet([1]: String, [2]: Int) {
  println("Hello, $name! You are $age years old.")
}

greet("Alice", 30)

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

Aname

Bage

Ccount

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using parameter names that do not match the variables used inside the function causes errors.

The parameters must be named 'name' and 'age' to match the print statement and function call.

5fill in blank

hard

Fill all three blanks to create a function with default arguments and call it with one argument.

Android Kotlin

fun greet([1]: String, [2]: Int = [3]) {
  println("Hello, $name! You are $age years old.")
}

greet("Charlie")

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

Aname

Bage

C25

D30

Attempts:

3 left

💡 Hint

Common Mistakes

Not providing a default value for the second parameter causes errors when calling with one argument.

The function has parameters 'name' and 'age' with a default value 25 for age, so calling greet("Charlie") works.

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