Understanding Project Structure in Jetpack Compose

Jetpack Compose has revolutionized UI development for Android by introducing a modern, declarative approach. Unlike traditional XML-based layouts, Jetpack Compose allows developers to build UIs using Kotlin code, simplifying state management and making UI components more reusable. However, for beginners and even experienced Android developers, understanding the project structure in Jetpack Compose is essential to maintain scalability and modularity. This article explores the standard project structure in Jetpack Compose and best practices for organizing your code effectively.

1. Overview of a Jetpack Compose Project

When you create a new Jetpack Compose project in Android Studio, the default project structure follows a modular organization that includes essential components such as UI, data, and domain layers. Here’s an overview of the key components:

a) MainActivity.kt

This is the entry point of your application, which typically hosts the setContent {} function that initializes the UI with Compose components.

b) com.example.app.ui

This package contains all UI-related components, including Composables, themes, and navigation.

c) com.example.app.data

This package is responsible for managing the data layer, such as repositories and database-related components.

d) com.example.app.domain

This package (optional) holds business logic, use cases, and models that interact between data and UI layers.

e) com.example.app.navigation

If your app has multiple screens, this package will manage navigation between Composables using Jetpack Navigation.

Now, let’s break down each of these components in detail.

2. Understanding the UI Layer in Jetpack Compose

a) MainActivity.kt

The MainActivity serves as the starting point of a Jetpack Compose application. It typically contains:

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MyApp()
        }
    }
}

Here, setContent {} is used to define the UI of the application using composable functions.

b) Composable Functions

Jetpack Compose is built around composable functions, which define UI elements declaratively. These functions are annotated with @Composable and return UI elements.

Example:

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

c) UI Theming and Styling

Jetpack Compose provides a dedicated theming system using Material Design. Themes are typically defined in the theme package under com.example.app.ui.theme.

Example:

@Composable
fun MyAppTheme(content: @Composable () -> Unit) {
    MaterialTheme(
        colors = lightColors(
            primary = Color.Blue,
            secondary = Color.Green
        ),
        typography = Typography,
        shapes = Shapes,
        content = content
    )
}

3. Managing Navigation in Jetpack Compose

Jetpack Compose uses the Navigation component to handle screen transitions declaratively. Navigation is managed by the NavController and NavHost.

a) Defining a Navigation Graph

@Composable
fun NavGraph(navController: NavController) {
    NavHost(navController, startDestination = "home") {
        composable("home") { HomeScreen(navController) }
        composable("details") { DetailsScreen(navController) }
    }
}

b) Navigating Between Screens

Button(onClick = { navController.navigate("details") }) {
    Text("Go to Details")
}

4. Data Layer and State Management

a) ViewModel Integration

Jetpack Compose integrates with ViewModel for state management. The viewModel() function retrieves the ViewModel in Composables.

Example:

class MyViewModel : ViewModel() {
    private val _text = MutableLiveData("Hello, Compose!")
    val text: LiveData<String> = _text
}

@Composable
fun MyScreen(viewModel: MyViewModel = viewModel()) {
    val text by viewModel.text.observeAsState("Default")
    Text(text = text)
}

b) State Hoisting

State hoisting in Jetpack Compose follows the principle of lifting state to a common ancestor.

Example:

@Composable
fun ParentComposable() {
    var text by remember { mutableStateOf("Hello") }
    ChildComposable(text) { text = it }
}

@Composable
fun ChildComposable(text: String, onTextChange: (String) -> Unit) {
    TextField(value = text, onValueChange = onTextChange)
}

5. Best Practices for Structuring a Jetpack Compose Project

To keep your project scalable and maintainable, consider these best practices:

• Follow MVVM Architecture: Separate UI, data, and domain layers to keep the project modular.
• Use State Management: Utilize ViewModel and remember-state APIs to manage state efficiently.
• Encapsulate Composables: Make Composables reusable and avoid direct state management inside them.
• Use Navigation Graphs: Maintain navigation structure separately for easy modifications.
• Leverage Theming: Centralize theming styles for consistent UI design.
• Write Unit Tests: Test Composables using composeTestRule for UI behavior validation.

Conclusion

Understanding the project structure in Jetpack Compose is crucial for developing scalable and maintainable applications. By following the recommended structure—dividing the project into UI, data, and domain layers—you ensure clean code organization and better state management. With features like declarative UI, state hoisting, and composable navigation, Jetpack Compose makes modern Android UI development more efficient and enjoyable. As you delve deeper, refining these best practices will help you build robust applications with ease.

By following this guide, you’ll have a strong foundation in organizing a Jetpack Compose project efficiently. Happy coding!