Android Academy · Lesson

Your First Composable

Create and preview a composable function.

Your First Composable is a free Android Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Android Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Your First Composable

A composable is just a Kotlin function marked with @Composable. Let's write one that greets a user by name.

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

The @Composable Annotation

The @Composable annotation tells the compiler this function can emit UI and can call other composables. Without it, you cannot call Text, Button, or other UI functions.

Naming Convention

Composables that emit UI are named with PascalCase nouns, like Greeting or ProfileCard — similar to a class. This signals "this draws something" rather than "this returns a value".

Parameters Drive the UI

A composable takes parameters just like any function. Those parameters are your inputs. Different arguments produce different UI.

@Composable
fun Greeting(name: String) {
    Text(text = "Welcome, $name")
}
// Greeting("Sam") and Greeting("Mia") render different text

Calling Composables

Composables can only be called from other composables. You compose a screen by nesting calls.

@Composable
fun WelcomeScreen() {
    Greeting(name = "Ada")
    Greeting(name = "Grace")
}

Hosting with setContent

To actually display composables, an Activity calls setContent { } in onCreate. The lambda is the root of your Compose UI.

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

Composables Return Unit

Notice composables do not return a UI object. They have return type Unit and emit UI as a side effect of being called. You build UI by calling, not by returning values.

Default Parameters

Kotlin default arguments work great here. Give a parameter a default so callers can omit it.

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

Reusing Composables

Because they are functions, composables are reusable. Define Greeting once and call it anywhere with different names. This is how you avoid duplicating UI code.

Keep Them Small

Good composables are small and focused. One composable should describe one logical chunk of UI. Compose larger screens by combining small composables.

Putting It Together

Here is a complete first composable wired into an activity. Running it on a device shows "Hello, Compose!".

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

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

Quick Check

What does the @Composable annotation allow a function to do?

Recap

You wrote your first composable. Remember:

Mark UI functions with @Composable.
Use PascalCase names.
Parameters are the inputs that shape the UI.
setContent { } hosts composables in an activity.

Frequently asked questions

Is the “Your First Composable” lesson free?

Yes — the full text of “Your First Composable” is free to read here on the web, and the Android Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Android Academy course, upgrade to CoddyKit PRO.

What will I learn in “Your First Composable”?

Create and preview a composable function. You practise Android Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Android Academy?

No prior experience is required. Android Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Your First Composable” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Android Academy lesson?

Yes. Every Android Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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