Jetpack Compose Tutorial for Android: Getting Began

Replace be aware: 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. Based on 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 previous means.”

Working methods 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 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 in the event you’re acquainted with declarative net frameworks akin to React, Angular or Vue.

The Jetpack Compose method is a big departure from Android’s authentic XML UI toolkit, now known as Views. Views was modeled after previous desktop UI frameworks and dates to Android’s starting. In Views, you employ a mechanism akin to 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 purposes written in Kotlin. With Jetpack Compose, you now not need to context-switch to XML when designing your app’s UI; you do every little thing 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 complicated 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 working the newest steady 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. Recently, Google has been upgrading Android Studio at a livid tempo, and the code under won’t work on earlier variations.

Be aware: “Test for Updates” is your pal! On the macOS model of Android Studio, you’ll discover it underneath the Android Studio menu. In the event you’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 Mission…. Relying on the way you final resized the New Mission window, you’ll both see one thing like this:

or this:

Both means, 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 important to state issues explicitly so a compiler can perceive them, that is thought of a refined trace. You need to infer that Jetpack Compose is predicted to be the popular means 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, title the mission My First Compose App and click on the End button.

Good day, Android!

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

To see what’s behind this notably unexciting display, 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 totally different is the remainder of the code in onCreate(). When constructing Android UIs the previous means — which is 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 mission, 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 top 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(title: String, modifier: Modifier = Modifier) {
 Textual content(
   textual content = "Good day $title!",
   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 operate (or composable for brief), which implies it receives knowledge and generates a UI factor in response. One cause to make it clear {that a} operate is composable is that composable capabilities can solely be known as by different composable capabilities. setContent() which calls Greeting() is a composable.
• It has parameters. As a operate, it has parameters (or, in the event you favor, it takes arguments). That makes composables versatile, permitting you to move state to them. In the event you’re conversant in programming in React, composable parameters are Jetpack Compose’s model of props.
• It’s a Unit operate. It has no return worth. As a substitute, it causes a person interface factor to be drawn onscreen. Useful programming language purists would name this a facet impact; we Jetpack Composers favor to say that composables emit UI parts.
• Its title is a CapitalizedNoun. The conference is that composable operate names are nouns capitalized in PascalCase. It helps distinguish composables from odd capabilities and strategies, the place the conference is to make their names verbs that use camelCase capitalization.
• It comprises a name to a way known as Textual content(). Textual content() is one among Jetpack Compose’s built-in composables, and given a string, it emits a textual content view containing that string.