Jetpack Compose: The new Way of Building Android UI

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Jetpack Compose: The new Way of Building Android UI Umar Saidu Auna Software Engineer, gidimo, A tech community organizer. Kano @umarauna

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Challenges

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Challenges findViewById() – XML data binding and view binding APIs are showing signs of ageing RecyclerView View Class keeps getting bigger and bigger ...

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Jetpack Compose

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Jetpack Compose Modern toolkit for building native Android UI. Jetpack Compose simplifies and accelerates UI development on Android with less code, powerful tools, and intuitive Kotlin APIs.

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Inspired by 1. React 2. Litho 3. Vue.js 4. Flutter ... but it’s written completely in Kotlin and is fully compatible with the existing Android view system.

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Declarative UI

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Declarative UI Declarative UI is a UI that’s designed in a declarative way. You describe what it should be like.

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Declarative This pattern is an emerging trend that allows the developers to design the user interface based on the data received. This is the most common paradigm; it involves having a separate prototype/model of the application’s UI. Imperative

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Declarative This design paradigm makes use of one programming language to create an entire application. A good example is XML layouts in Android. We design the widgets and components which are then rendered for the user to see and interact with. Imperative

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Declarative This on the other hand focuses on the what This design focuses on the how rather than the what Imperative

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“Everything is a function”

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Compose Everywhere View/XML -> UI as Objects Compose -> UI as Function

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Goal ● Simplify ● Less code ● Fix what’s broken

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Components ● Layouts ○ Column ○ Row ○ Flex(column/row) ○ Box(similar to Framelayout) ○ ConstraintLayout(almost done)

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Components ● Built-in Components ○ Button ○ Text ○ Checkbox ○ Navigation Drawer ○ Navigation Bar ○ Checkbox ○ AppBar

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Components ● Custom View ○ Draw ○ Layout

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Getting Started

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New Project

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Existing Project(gradle:app)

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Existing Project(gradle:module)

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Jetpack Compose Basics

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Compose function ● Regular function annotated with @Composable. ● Enables your function to call other @Composable functions within it.

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Compose in Android app ● Use setContent to define layout ● Call composable function instead of XML file

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Compose in Android app ● Use setContent to define layout ● Call composable function instead of XML file

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Preview Change with @Preview ● Prepare Android Studio 4.0 Preview ● Set Preview Content with @Preview annotation. ● Build Project.

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Live Preview in Android Studio

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Modifiers ● Are used to modify the composable UI elements for example adding margin, padding or defining the width and height. ● Available modifiers are:background(), clickable, scrollable, draggable, swipeable, width(), height(), size(), padding() . . . . .

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3 2 1

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Compose in Kotlin Mix Compose UI with any Kotlin function, example: for loop

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LAzy COlumn A LazyColumn is a vertically scrolling list that only composes and lays out the currently visible items. It’s similar to a Recyclerview in the classic Android View system.

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@Composable fun Planets(planets: List) { // A surface container using the 'background' color from the theme Surface(color = MaterialTheme .colors.background) { Column() { Text( text = stringResource (R.string.planets), style = MaterialTheme .typography.h4, modifier = Modifier.padding(10.dp) ) val planet = planets.maxByOrNull { it.moon } Text( text = getGreetingMessage (planet), style = MaterialTheme .typography.h6, modifier = Modifier.padding(10.dp) ) LazyColumn() { items(planets) { planet -> PlanetImageList (planet) } } } } }

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Getting interesting right?

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Codelabs • goo.gle/compose-pathway • goo.gle/compose-samples • goo.gle/compose-docs • goo.gle/compose-slack • goo.gle/compose-feedback • https://developer.android.com/jetpack/compose/tutorial • https://foso.github.io/Jetpack-Compose-Playground/material/button/