How does Jetpack Compose work?

Jetpack Compose is a declarative UI framework for Android built on the Kotlin language. It is based on the principle of "UI as a function of state".

Key concepts:

• Declarativeness: The developer describes how the UI should look for a given state, not how to change it (imperative approach).
• Composition: UI is built from small, reusable elements — Composable functions.
• State: Data that defines the current appearance of the UI. Changing the state automatically triggers a redraw (recomposition).
• Recomposition: The process of re-invoking Composable functions when the state changes to update the UI. Compose intelligently redraws only the parts of the UI that have actually changed.
• Kotlin: Compose is fully written in Kotlin and uses its features (e.g., lambdas, coroutines) to create expressive and concise code.

Workflow:

1. The developer defines the UI using Composable functions.
2. These functions describe how the UI should look based on the current state.
3. Compose creates a tree of UI elements in memory.
4. When the state changes, Compose initiates the recomposition process.
5. During recomposition, Compose determines which parts of the UI need updating.
6. It calls only those Composable functions whose state has changed or on which they depend.
7. Compose uses techniques like "slots" and comparison of previous and new states of Composable functions to minimize work during recomposition. Changes are applied to the actual UI.

Example of a Composable function:

@Composable
fun Greeting(name: String) {
    Text(text = "Hello, $name!")
}