Jetpack Compose Tutorial for Android: Getting Began

Replace notice: 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 growth. Based on a survey of the cellular growth ecosystem taken in late 2022 by the Cellular Native Basis, half of Android builders are constructing apps with Jetpack Compose. The opposite half are constructing them “the previous manner.”

Working techniques evolve, and Android — the world’s hottest OS — isn’t any exception. When a platform the dimensions of Android makes a change this huge, the primary builders who embrace the change achieve a major 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 a substitute 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 when you’re acquainted with declarative net frameworks equivalent to React, Angular or Vue.

The Jetpack Compose strategy is a major departure from Android’s unique XML UI toolkit, now referred to as Views. Views was modeled after previous desktop UI frameworks and dates to Android’s starting. In Views, you employ a mechanism equivalent to findViewById() or view binding to attach UI parts to code. This crucial strategy is easy 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 purposes written in Kotlin. With Jetpack Compose, you now not need to context-switch to XML when designing your app’s UI; you do all the pieces in Kotlin.

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

• A easy check run app, which you’ll construct from scratch, beginning with File → New.
• A extra advanced cookbook app that can show a listing of recipe playing cards containing pictures and textual content. You’ll construct this utilizing a starter venture.

Your First Jetpack Compose App

Make sure you’re operating the most recent 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 — have been constructed utilizing the Flamingo model of Android Studio. Currently, Google has been upgrading Android Studio at a livid tempo, and the code under may not work on earlier variations.

Observe: “Verify for Updates” is your buddy! On the macOS model of Android Studio, you’ll discover it underneath the Android Studio menu. For those who’re a Home windows- or Linux-based Android Studio person, you’ll discover it underneath the Assist menu.

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

or this:

Both manner, you’ll see the first template within the record is for an Empty Exercise venture with the Jetpack Compose icon:

On the planet of programming, the place it’s important to state issues explicitly so a compiler can perceive them, that is thought of a delicate trace. It is best to infer that Jetpack Compose is predicted to be the popular manner 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 Venture window, identify the venture My First Compose App and click on the End button.

Hiya, Android!

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

To see what’s behind this significantly unexciting display screen, open MainActivity.kt. It nonetheless comprises 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 previous manner — which known as 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 venture, it appears like this:

setContent {
  MyFirstComposeAppTheme {
  // A floor container utilizing the 'background' shade from the theme
    Floor(
      modifier = Modifier.fillMaxSize(),
      shade = 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 referred to as Greeting(). You’ll discover its definition instantly after the MainActivity class:

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

As you see, Greeting() is the tactic that determines what seems onscreen if you run the app. You must also 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 suggests it receives information and generates a UI aspect in response. One cause to make it clear {that a} perform is composable is that composable features can solely be referred to as by different composable features. setContent() which calls Greeting() is a composable.
• It has parameters. As a perform, it has parameters (or, when you want, it takes arguments). That makes composables versatile, permitting you to go state to them. For those who’re acquainted with programming in React, composable parameters are Jetpack Compose’s model of props.
• It’s a Unit perform. It has no return worth. As a substitute, it causes a person interface aspect to be drawn onscreen. Purposeful programming language purists would name this a aspect 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 atypical features and strategies, the place the conference is to make their names verbs that use camelCase capitalization.
• It comprises a name to a way referred to 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.