The Lifecycle of Jetpack Compose Composables vs. Android View Lifecycle: A Quick Dive

In Android development, understanding the lifecycle of UI components is crucial to creating responsive and efficient applications. Traditionally, Android UIs have been built using Views and the ViewGroup hierarchy. However, with the introduction of Jetpack Compose, a new paradigm for building UIs has emerged. While both systems aim to achieve similar goals, their lifecycles differ significantly due to their underlying architectures. In this blog, we’ll explore the lifecycle of Composables in Jetpack Compose, compare it to the traditional Android View lifecycle, and understand how these differences impact development.

1. The Android View Lifecycle

The traditional Android View system relies on a hierarchical tree structure, where UI components are organized within ViewGroups. The lifecycle of these Views is tightly coupled with the Activity or Fragment hosting them. Here’s a quick overview of the key lifecycle events:

• onCreate(): This is where you usually inflate the layout containing your Views.
• onStart(): Views become visible, but they are not interactive yet.
• onResume(): Views are fully visible and ready to interact with the user.
• onPause(): The UI is partially obscured, often because another activity is coming to the foreground.
• onStop(): The UI is no longer visible to the user.
• onDestroy() : The final cleanup happens here, and all resources tied to the View should be released.

Each View within this hierarchy has its own lifecycle callbacks like onAttachedToWindow() and onDetachedFromWindow(), which are invoked as the View becomes part of or is removed from the window.

2. The Composable Lifecycle in Jetpack Compose

Jetpack Compose, being a declarative UI framework, approaches UI construction differently. Instead of manually managing a tree of Views, you describe the UI in terms of Composables — functions that define the UI and its behavior in a declarative way. Compose handles the rendering, updating, and disposal of these Composables efficiently based on state changes.

Key Points of the Composable Lifecycle:

• Composition: When a Composable function is first called, the system “composes” it. This means that the UI tree is created based on the current state. This is the equivalent of inflating a View in the traditional system.
• Recomposition: This is one of the core concepts in Compose. When the state that a Composable depends on changes, the framework re-invokes the Composable function to update the UI. Only the parts of the UI tree that need to change are recomposed, making this process very efficient.
• Disposal: When a Composable leaves the composition (e.g., due to a state change or navigation), the framework cleans up its resources. This is similar to the destruction phase in the View lifecycle, though it happens at a much more granular level.
• Side Effects Management: Compose provides mechanisms like LaunchedEffect, DisposableEffect, and remember to manage side effects during the Composable lifecycle. These allow you to run code during composition, when a Composable enters the composition, and when it leaves, respectively.

Lifecycle Events in Compose:

• LaunchedEffect: This is analogous to onStart or onResume in the View system. You use it to start a coroutine when the Composable enters the composition.
• DisposableEffect: This is similar to onPause or onStop, where you can perform cleanup when the Composable leaves the composition.

You can read more about compose side effects here

3. Key Differences Between View and Composable Lifecycles

Understanding the differences between these two systems is key to transitioning from Views to Composables or using both in the same project. Here are the major distinctions:

• Declarative vs. Imperative: The View lifecycle is imperative — you directly control the lifecycle events of the Views. In Compose, the lifecycle is declarative — Compose handles the lifecycle based on state changes, and you declare what the UI should look like for a given state.
• Efficiency: Compose’s recomposition process is more efficient than the traditional View hierarchy updates, as it only re-renders the parts of the UI that have changed. The View system typically requires you to handle updates manually, which can be less efficient.
• State Management: In the View system, managing UI state across lifecycle events often requires using ViewModel, LiveData, or savedInstanceState. In Compose, state management is more integrated and often simpler, thanks to tools like remember and MutableState.
• Lifecycle Ownership: In the View system, Views are tightly coupled to the lifecycle of their hosting Activity or Fragment. In Compose, while Composables can be hosted within an Activity or Fragment, their lifecycle is more dynamic and is primarily driven by the composition process.

4. Practical Implications for Developers

For developers, these lifecycle differences have several practical implications:

• Simplified State Management: The declarative nature of Compose simplifies state management. You no longer need to manually save and restore state in most cases, as the framework handles much of this automatically.
• Performance Improvements: Compose’s recomposition mechanism can lead to performance improvements, especially in complex UIs with dynamic content.
• Migration Considerations: If you’re migrating from Views to Compose, understanding these lifecycle differences is crucial. You’ll need to adapt your mental model and possibly refactor code that assumes the imperative View lifecycle.

Conclusion

The lifecycle of Composables in Jetpack Compose represents a significant shift from the traditional Android View lifecycle. While both systems aim to create and manage UI components efficiently, Compose’s declarative approach and its dynamic handling of UI updates offer a more modern and streamlined development experience. Understanding these differences allows developers to make the most of Compose’s capabilities, leading to more responsive, maintainable, and efficient applications.

Whether you’re building a new app from scratch or refactoring an existing one, embracing the Compose lifecycle can unlock new possibilities in how you think about and build Android UIs.