ViewModel creation in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

Correct ViewModel class declaration

Which option correctly declares a simple ViewModel class in Kotlin for Android?

A class MyViewModel : ViewModel() {}

B class MyViewModel extends ViewModel {}

C class MyViewModel : ViewModel {}

D fun MyViewModel() : ViewModel {}

💡 Hint

Remember Kotlin uses ':' for inheritance and parentheses for constructor calls.

In Kotlin, to create a ViewModel class, you extend ViewModel with a colon and call its constructor with parentheses. Option A follows this syntax correctly.

❓ ui_behavior

intermediate

ViewModel lifecycle behavior

What happens to a ViewModel instance when the associated Activity is rotated (configuration change)?

A The ViewModel is destroyed and recreated with the Activity.

B The ViewModel instance is retained and reused by the new Activity instance.

C The ViewModel is paused and resumed after rotation.

D The ViewModel is converted to a singleton shared across all Activities.

💡 Hint

Think about how ViewModel helps keep UI data during screen rotations.

ViewModel survives configuration changes like rotation by being retained and reused by the new Activity instance, preventing data loss.

🧠 Conceptual

advanced

Purpose of ViewModel in MVVM architecture

What is the main role of a ViewModel in the MVVM pattern on Android?

A To handle UI rendering and user input directly.

B To replace the Activity and Fragment lifecycle methods.

C To store and manage UI-related data and handle business logic separate from UI.

D To manage database connections and network calls only.

💡 Hint

ViewModel acts as a bridge between UI and data layers.

ViewModel holds UI data and business logic, keeping it separate from UI controllers like Activities or Fragments, enabling cleaner code and lifecycle awareness.

🔧 Debug

advanced

Identify the error in ViewModel usage

What error will occur with this code snippet? val viewModel = ViewModelProvider(this).get(MyViewModel::class.java) class MyViewModel {}

Android Kotlin

val viewModel = ViewModelProvider(this).get(MyViewModel::class.java)

class MyViewModel {}

A No error, code runs correctly.

B Compile error: Missing parentheses in ViewModelProvider constructor.

C Runtime error: ViewModelProvider requires a Fragment, not Activity.

D Compile error: MyViewModel must extend ViewModel class.

💡 Hint

Check if MyViewModel inherits from the correct base class.

MyViewModel does not extend ViewModel, so ViewModelProvider cannot create its instance, causing a compile error.

❓ navigation

expert

ViewModel sharing between fragments

How can two fragments in the same Activity share the same ViewModel instance?

A Use ViewModelProvider with the Activity as the owner for both fragments.

B Create separate ViewModel instances in each fragment using their own ViewModelProvider(this).

C Pass ViewModel instance manually via fragment arguments bundle.

D Use a singleton ViewModel instance created outside the Activity.

💡 Hint

Think about the lifecycle owner scope when requesting ViewModel.

Using the Activity as the ViewModelStoreOwner allows fragments to share the same ViewModel instance tied to the Activity lifecycle.