Level 1

The Atom (Hello Compose)

Composable Functions

In modern Android, UI is not a separate XML file. It is a Kotlin function annotated with `@Composable`.

📚 Explanation

In Jetpack Compose, UI components are functions annotated with `@Composable`. The `setContent` function replaces the old `setContentView(R.layout.activity_main)` pattern. No XML layouts needed!

Note: Code execution is not available for Android/Kotlin in the browser. Use Android Studio to run and test the app.

kotlin

// MainActivity.kt
import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // This is the entry point. No setContentView(R.layout...)
        setContent {
            Greeting("Android Developer")
        }
    }
}

// A simple UI component
@Composable
fun Greeting(name: String) {
    // Material 3 Text component
    Text(text = "Hello, $name!")
}

Back to Android Levels Back to Developer Hub