Understanding the ViewModel Lifecycle in Android

In Android development, managing data and UI state efficiently is crucial, especially when dealing with configuration changes like screen rotations. The MVVM (Model-View-ViewModel) architecture, coupled with Android Jetpack's

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ViewModel

component, provides a robust solution. This module focuses on the lifecycle of a

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ViewModel

and how it interacts with the Android system, ensuring your app remains stable and responsive.

What is a ViewModel?

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ViewModel

is a class designed to store and manage UI-related data in a lifecycle-aware way. It survives configuration changes, such as screen rotations, preventing data loss. This means that when your Activity or Fragment is recreated, the

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ViewModel

instance remains the same, and the data it holds is preserved.

The ViewModel Lifecycle

Unlike Activities and Fragments,

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ViewModel

instances have a longer lifecycle. They are scoped to a specific

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ViewModelStoreOwner

(typically an Activity or Fragment). A

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ViewModel

is created when it's first requested by a

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ViewModelStoreOwner

and is destroyed when the

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ViewModelStoreOwner

is permanently destroyed (e.g., when an Activity finishes).

ViewModel survives configuration changes.

When an Activity or Fragment is recreated due to configuration changes (like screen rotation), the existing ViewModel instance is retained. This prevents data loss and avoids unnecessary data re-fetching.

The ViewModel is associated with a ViewModelStoreOwner. When a configuration change occurs, the ViewModelStoreOwner is destroyed and recreated. However, the ViewModelStore associated with the original owner is not destroyed. Instead, it's passed to the newly created owner. This allows the ViewModel to persist across these changes. The ViewModel's onCleared() method is called only when the associated ViewModelStoreOwner is permanently destroyed, not during temporary configuration changes.

ViewModel vs. Activity/Fragment Lifecycle

Feature	Activity/Fragment	ViewModel
Lifecycle Scope	Activity/Fragment instance	ViewModelStoreOwner (Activity/Fragment)
Survival on Config Change	Destroyed and recreated	Persists
Data Persistence	Data is lost unless saved explicitly	Data is retained
Destruction Trigger	Activity finishes or Fragment is detached	ViewModelStoreOwner is permanently destroyed

ViewModel and Play Store Publishing

While

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ViewModel

directly manages UI data and its lifecycle, understanding its robustness is indirectly beneficial for Play Store publishing. Apps that handle configuration changes gracefully, without crashing or losing user data, provide a better user experience. This leads to higher user satisfaction and potentially better app store ratings and reviews, which are factors considered during the publishing process and by users deciding to download or keep an app.

Think of ViewModel as a dedicated data manager that stays with your screen's 'concept' even if the screen itself gets rebuilt. This is key for a smooth user experience.

Key Lifecycle Method: onCleared()

The

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ViewModel

class provides an

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onCleared()

method. This method is called when the

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ViewModel

is about to be destroyed. It's the ideal place to perform any necessary cleanup, such as cancelling coroutines, closing database connections, or unregistering listeners. This ensures that resources are properly released when the

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ViewModel

is no longer needed, preventing memory leaks.

When is the onCleared() method of a ViewModel called?

The onCleared() method is called when the ViewModel is about to be destroyed, which happens when its associated ViewModelStoreOwner is permanently destroyed.

ViewModel Scoping

The scope of a

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ViewModel

is determined by the

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ViewModelStoreOwner

it's associated with. For example, a

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ViewModel

scoped to an Activity will live as long as that Activity. If you need a

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ViewModel

to live across multiple Activities or Fragments, you can scope it to a parent Activity or even the Application itself. This is managed using

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ViewModelProvider

and

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ViewModelFactory

The lifecycle of a ViewModel is tied to its ViewModelStoreOwner. When the owner is created, the ViewModel is instantiated. If the owner is destroyed and recreated due to configuration changes, the same ViewModel instance is reused. The ViewModel is only truly destroyed when the owner is permanently removed from the back stack or finishes. This persistence is visualized by showing the ViewModel's existence continuing while the Activity/Fragment might be recreated.

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Learning Resources

ViewModel Overview | Android Developers(documentation)

The official Android Developers documentation provides a comprehensive overview of ViewModel, its purpose, and lifecycle management.

ViewModel Lifecycle | Android Developers(documentation)

This section of the Android Developers documentation specifically details the lifecycle of a ViewModel and how it relates to configuration changes.

Save and Restore UI State | Android Developers(documentation)

Learn how to save and restore UI state, which often complements ViewModel usage for more complex scenarios.

Android Jetpack ViewModel Tutorial(tutorial)

A practical tutorial demonstrating how to implement and use ViewModel in an Android application.

Understanding ViewModel Lifecycle in Android(blog)

A blog post that dives deeper into the ViewModel lifecycle, explaining its behavior with clear examples.

MVVM Architecture in Android(blog)

An article explaining the MVVM architecture pattern and how ViewModel fits into it for Android development.

Android ViewModel Lifecycle Explained(video)

A video explanation that visually breaks down the ViewModel lifecycle and its importance in Android apps.

Jetpack ViewModel: Lifecycle-Aware(video)

Another video resource focusing on the lifecycle-aware nature of Jetpack ViewModel and its benefits.

ViewModel (Android Architecture Components)(wikipedia)

A Wikipedia entry providing a general overview and context for Android's ViewModel component.

Best Practices for App Development and Publishing(documentation)

General best practices for Android app development and publishing, which indirectly relate to the stability and user experience provided by components like ViewModel.

`ViewModel` lifecycle

Understanding the ViewModel Lifecycle in Android

What is a ViewModel?

The ViewModel Lifecycle

ViewModel survives configuration changes.

ViewModel vs. Activity/Fragment Lifecycle

ViewModel and Play Store Publishing

Key Lifecycle Method: onCleared()

ViewModel Scoping

Learning Resources