ViewModel creation in Android Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a ViewModel in Android development?

A ViewModel is a class that holds UI data and survives configuration changes like screen rotations. It helps keep data separate from UI controllers like Activities or Fragments.

beginner

How do you create a simple ViewModel class in Kotlin?

You create a class that extends <code>ViewModel</code>. For example:<br><pre>class MyViewModel : ViewModel() { }</pre>

beginner

Why should UI data be stored in a ViewModel instead of an Activity?

Because ViewModel survives configuration changes, it prevents data loss when the screen rotates. Activities get destroyed and recreated, losing their data.

intermediate

How do you obtain a ViewModel instance inside an Activity?

Use the ViewModelProvider like this:<br>

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

intermediate

What is the benefit of using LiveData inside a ViewModel?

LiveData holds data that UI can observe. It updates the UI automatically when data changes, and respects lifecycle to avoid crashes.

What does a ViewModel help with in Android apps?

A Managing network connections

B Drawing UI elements on screen

C Keeping UI data during screen rotations

D Handling user input events

ViewModel keeps UI data safe during configuration changes like screen rotations.

Which class should your ViewModel extend?

A Activity

B ViewModel

C Fragment

D Application

A ViewModel class must extend the Android ViewModel class.

How do you get a ViewModel instance in an Activity?

A new ViewModel()

B findViewById()

C getSystemService()

D ViewModelProvider(this).get()

Use ViewModelProvider with the Activity context to get the ViewModel.

What happens to data stored in an Activity when the screen rotates?

A It is lost unless saved

B It is preserved automatically

C It is sent to the server

D It is cached permanently

Activity is destroyed and recreated on rotation, so data is lost unless saved elsewhere.

Why use LiveData inside a ViewModel?

A To observe data changes safely

B To draw graphics

C To handle user clicks

D To store files

LiveData lets UI observe data changes and updates automatically respecting lifecycle.

Explain how to create and use a ViewModel in an Android app.

Think about separating UI data from Activity lifecycle.

Describe why ViewModel is important for handling screen rotations.

Imagine what happens when you turn your phone sideways.