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 growth. Based on a survey of the cell growth 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 approach.”

Working techniques evolve, and Android — the world’s hottest OS — is not any exception. When a platform the dimensions of Android makes a change this large, the primary builders who embrace the change acquire a big benefit. With half the Android builders nonetheless ready to make the leap, the time to be taught 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 utilize Kotlin code to declaratively specify how the UI ought to look and behave in numerous 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 case you’re acquainted with declarative net frameworks similar to React, Angular or Vue.

The Jetpack Compose strategy is a big departure from Android’s unique XML UI toolkit, now known as Views. Views was modeled after previous desktop UI frameworks and dates to Android’s starting. In Views, you utilize a mechanism similar to findViewById() or view binding to attach UI components 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 not need to context-switch to XML when designing your app’s UI; you do every 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 advanced cookbook app that may show an inventory of recipe playing cards containing photos and textual content. You’ll construct this utilizing a starter undertaking.

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. Recently, Google has been upgrading Android Studio at a livid tempo, and the code under won’t work on earlier variations.

Observe: “Verify for Updates” is your pal! On the macOS model of Android Studio, you’ll discover it underneath the Android Studio menu. Should 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 Challenge…. Relying on the way you final resized the New Challenge window, you’ll both see one thing like this:

or this:

Both approach, you’ll see the first template within the checklist is for an Empty Exercise undertaking 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 be taught it, the higher.

Choose the Jetpack Compose Empty Exercise template and click on Subsequent. Within the following New Challenge window, title the undertaking My First Compose App and click on the End button.

Good day, Android!

As soon as Android Studio completed constructing the undertaking, run the app. It is best 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() technique, 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 approach — which is named Views — onCreate() calls the setContentView() technique and passes it the ID of the view’s XML file, which Android makes use of to render the onscreen components. In Jetpack Compose, onCreate() calls a way named setContent(), and within the default undertaking, 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 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 once you run the app. You must also discover the next components of this technique:

• It’s annotated with @Composable. This informs the compiler that Greeting() is a composable perform (or composable for brief), which implies it receives information and generates a UI aspect in response. One purpose 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 case you desire, it takes arguments). That makes composables versatile, permitting you to cross state to them. Should you’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 consumer interface aspect to be drawn onscreen. Useful programming language purists would name this a aspect impact; we Jetpack Composers desire to say that composables emit UI components.
• Its title is a CapitalizedNoun. The conference is that composable perform names are nouns capitalized in PascalCase. It helps distinguish composables from odd features 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 in all Jetpack Compose’s built-in composables, and given a string, it emits a textual content view containing that string.