ViewModel creation in Android Kotlin

Introduction

A ViewModel helps keep your app data safe when the screen changes or rotates. It holds data for the screen and keeps it alive.

When you want to keep user data safe during screen rotation.

When you need to share data between different parts of the app screen.

When you want to separate data logic from the screen design.

When you want to avoid losing data after temporary app pauses.

When you want to make your app easier to test and maintain.

Syntax

Android Kotlin

class MyViewModel : ViewModel() {
    // Your data and functions here
}

ViewModel classes extend the ViewModel base class.

They do not hold references to UI elements to avoid memory leaks.

Examples

This ViewModel holds a simple counter and a function to increase it.

Android Kotlin

class CounterViewModel : ViewModel() {
    var count = 0

    fun increment() {
        count++
    }
}

This ViewModel holds a user name using LiveData to update the UI automatically.

Android Kotlin

class UserViewModel : ViewModel() {
    val userName = MutableLiveData<String>()

    fun setUserName(name: String) {
        userName.value = name
    }
}

Sample App

This ViewModel holds a message that can be shown on the screen. It starts with a greeting.

Android Kotlin

import androidx.lifecycle.ViewModel
import androidx.lifecycle.MutableLiveData

class SimpleViewModel : ViewModel() {
    val message = MutableLiveData<String>()

    init {
        message.value = "Hello from ViewModel!"
    }
}

Important Notes

ViewModels survive configuration changes like screen rotation.

Do not store UI elements or Context inside ViewModel to avoid memory leaks.

Use LiveData inside ViewModel to notify UI about data changes.

Summary

ViewModel keeps data safe during screen changes.

Create ViewModel by extending the ViewModel class.

Use LiveData inside ViewModel to update UI reactively.