Jetpack Compose is a modern UI toolkit designed to simplify Android app development. It replaces the traditional XML-based UI approach with a declarative programming model, making it easier to create interactive and dynamic user interfaces. If you’re new to Compose, this guide will walk you through everything you need to know—from setup to building a simple UI.

Why Jetpack Compose?

Jetpack Compose brings several advantages over traditional Android UI development:

• Less Boilerplate Code: No need to write complex XML layouts.
• Declarative UI: Define UI components based on state, making them easier to update.
• Improved Performance: Compose draws everything directly, removing unnecessary layout passes.
• Seamless Integration with Kotlin: Designed to work natively with Kotlin and Coroutines.
• Better Maintainability: UI components are modular and reusable.

Setting Up Compose in Your Project

Before you start, ensure that you have:

• The latest version of Android Studio (recommended: Giraffe or later)
• Kotlin support enabled in your project

Add Dependencies

In your project’s build.gradle (Module: app), add the necessary Jetpack Compose dependencies:

android {
    composeOptions {
        kotlinCompilerExtensionVersion = "1.5.4"
    }
}

dependencies {
    implementation("androidx.compose.ui:ui:1.5.4")
    implementation("androidx.compose.material:material:1.5.4")
    implementation("androidx.compose.ui:ui-tooling-preview:1.5.4")
    implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.6.2")
}

Once added, sync your project to fetch dependencies.

Understanding Composable Functions

At the core of Jetpack Compose are @Composable functions, which define UI components.

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

To display this function in an activity, use setContent inside onCreate:

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

Previewing UI in Android Studio

Jetpack Compose allows you to preview UI components without running the app. Use the @Preview annotation:

@Preview(showBackground = true)
@Composable
fun PreviewGreeting() {
    Greeting("Android")
}

Click on Build & Refresh in the preview window to see your UI instantly.

Common UI Components in Jetpack Compose

Jetpack Compose offers built-in UI elements like Text, Button, Column, Row, Image, etc. Here are some of the most used ones:

Text Component

@Composable
fun SimpleText() {
    Text(text = "Hello, Compose!", fontSize = 24.sp)
}

Button Component

@Composable
fun ClickableButton() {
    Button(onClick = { /* Handle click */ }) {
        Text("Click Me")
    }
}

Layouts: Column & Row

Jetpack Compose provides flexible layout components.

Column Layout (Vertical List)

@Composable
fun ColumnExample() {
    Column {
        Text("Item 1")
        Text("Item 2")
    }
}

Row Layout (Horizontal List)

@Composable
fun RowExample() {
    Row {
        Text("Item 1")
        Text("Item 2")
    }
}

Managing State in Jetpack Compose

Jetpack Compose uses State to manage dynamic content. The UI automatically updates when the state changes.

@Composable
fun Counter() {
    var count by remember { mutableStateOf(0) }

    Column {
        Text(text = "Count: $count")
        Button(onClick = { count++ }) {
            Text("Increase")
        }
    }
}

• remember { mutableStateOf(0) } stores and updates the UI state.
• Clicking the button increases the counter, and the UI updates instantly.

Theming with Material Design

Jetpack Compose supports Material Design principles out of the box.

@Composable
fun MyAppTheme(content: @Composable () -> Unit) {
    MaterialTheme {
        content()
    }
}

You can further customize colors, typography, and shapes using the MaterialTheme system.

Conclusion

Jetpack Compose is a game-changer for Android UI development, offering a cleaner, more efficient way to build interactive applications. With its declarative approach, built-in state management, and seamless integration with Kotlin, it’s an excellent choice for modern Android apps.

• Less boilerplate
• More readable code
• Better performance
• Faster development

Now that you have a solid understanding of the basics, why not start building your own Compose UI?