Jetpack Compose Tutorial for Android: Getting Began

Replace observe: Joey deVilla up to date this tutorial for Android Studio Giraffe, Kotlin 1.9 and Android 14. Alex Sullivan wrote the unique.

We’re at an thrilling level in Android improvement. In keeping with a survey of the cell improvement ecosystem taken in late 2022 by the Cell Native Basis, half of Android builders are constructing apps with Jetpack Compose. The opposite half are constructing them “the outdated approach.”

Working techniques evolve, and Android — the world’s hottest OS — is not any exception. When a platform the scale of Android makes a change this huge, the primary builders who embrace the change achieve a big benefit. With half the Android builders nonetheless ready to make the leap, the time to study Jetpack Compose is now.

What’s Jetpack Compose?

Launched in July 2021, Jetpack Compose is a UI toolkit that updates the method of constructing Android apps. As an alternative of XML, you employ Kotlin code to declaratively specify how the UI ought to look and behave in varied states. You don’t have to fret how the UI strikes amongst these states — Jetpack Compose takes care of that. You’ll discover it acquainted in the event you’re acquainted with declarative net frameworks reminiscent of React, Angular or Vue.

The Jetpack Compose method is a big departure from Android’s unique XML UI toolkit, now known as Views. Views was modeled after outdated desktop UI frameworks and dates to Android’s starting. In Views, you employ a mechanism reminiscent of findViewById() or view binding to attach UI parts to code. This crucial method is straightforward however requires defining how this system strikes amongst states and the way the UI ought to look and behave in these states.

Jetpack Compose is constructed with Kotlin, and it takes benefit of the options and design philosophy of Kotlin language. It’s designed to be used in functions written in Kotlin. With Jetpack Compose, you not need to context-switch to XML when designing your app’s UI; you do every part in Kotlin.

On this tutorial, you’ll construct two Jetpack Compose apps:

• A easy take a look at run app, which you’ll construct from scratch, beginning with File → New.
• A extra advanced cookbook app that may show an inventory of recipe playing cards containing photos and textual content. You’ll construct this utilizing a starter mission.

Your First Jetpack Compose App

Make sure you’re operating the newest secure model of Android Studio. Each apps on this tutorial — the easy app you’re about to construct and the cookbook app you’ll construct afterward — had been constructed utilizing the Flamingo model of Android Studio. Currently, Google has been upgrading Android Studio at a livid tempo, and the code beneath may not work on earlier variations.

Observe: “Verify for Updates” is your good friend! On the macOS model of Android Studio, you’ll discover it underneath the Android Studio menu. In case you’re a Home windows- or Linux-based Android Studio consumer, you’ll discover it underneath the Assist menu.

When you’ve confirmed your Android Studio is updated, launch it and choose File → New → New Mission…. Relying on the way you final resized the New Mission window, you’ll both see one thing like this:

or this:

Both approach, you’ll see the first template within the listing is for an Empty Exercise mission with the Jetpack Compose icon:

On this planet of programming, the place it’s a must to state issues explicitly so a compiler can perceive them, that is thought of a refined trace. It is best to infer that Jetpack Compose is predicted to be the popular approach for constructing Android UIs going ahead, and the earlier you study it, the higher.

Choose the Jetpack Compose Empty Exercise template and click on Subsequent. Within the following New Mission window, identify the mission My First Compose App and click on the End button.

Hi there, Android!

As soon as Android Studio completed constructing the mission, run the app. It is best to see one thing like this:

To see what’s behind this notably unexciting display screen, open MainActivity.kt. It nonetheless accommodates a MainActivity class and an onCreate() methodology, and onCreate() nonetheless calls on its counterpart in MainActivity’s superclass, ComponentActivity.

What’s completely different is the remainder of the code in onCreate(). When constructing Android UIs the outdated approach — which is named Views — onCreate() calls the setContentView() methodology and passes it the ID of the view’s XML file, which Android makes use of to render the onscreen parts. In Jetpack Compose, onCreate() calls a way named setContent(), and within the default mission, it seems to be like this:

setContent {
  MyFirstComposeAppTheme {
  // A floor container utilizing the 'background' colour from the theme
    Floor(
      modifier = Modifier.fillMaxSize(),
      colour = MaterialTheme.colorScheme.background
    ) {
     Greeting("Android")
    }
  }
}

setContent() takes a lambda as its parameter, and close to the tip of that lambda is a name to a way known as Greeting(). You’ll discover its definition instantly after the MainActivity class:

@Composable
enjoyable Greeting(identify: String, modifier: Modifier = Modifier) {
 Textual content(
   textual content = "Hi there $identify!",
   modifier = modifier
 )
}

As you see, Greeting() is the strategy that determines what seems onscreen while you run the app. You also needs to discover the next parts of this methodology:

• It’s annotated with @Composable. This informs the compiler that Greeting() is a composable perform (or composable for brief), which implies it receives knowledge and generates a UI aspect in response. One motive to make it clear {that a} perform is composable is that composable features can solely be known as by different composable features. setContent() which calls Greeting() is a composable.
• It has parameters. As a perform, it has parameters (or, in the event you want, it takes arguments). That makes composables versatile, permitting you to go state to them. In case you’re conversant in programming in React, composable parameters are Jetpack Compose’s model of props.
• It’s a Unit perform. It has no return worth. As an alternative, it causes a consumer interface aspect to be drawn onscreen. Purposeful programming language purists would name this a facet impact; we Jetpack Composers want to say that composables emit UI parts.
• Its identify is a CapitalizedNoun. The conference is that composable perform names are nouns capitalized in PascalCase. It helps distinguish composables from extraordinary features and strategies, the place the conference is to make their names verbs that use camelCase capitalization.
• It accommodates a name to a way known as Textual content(). Textual content() is one in every of Jetpack Compose’s built-in composables, and given a string, it emits a textual content view containing that string.