Unleashing the Potential of Jetpack Compose: Part I — Fundamentals and Advantages

Embrace a new era of Android UI development with Jetpack Compose!

Let’s Understand, what is Jetpack Compose?

This modern toolkit empowers you to create beautiful and responsive user interfaces with less code. Leveraging the power and expressiveness of Kotlin, Jetpack Compose simplifies UI development, improves maintainability, and elevates the overall developer experience.

Jetpack Compose is not a part of the framework. It’s a library — Jetpack Library

The fundamental building blocks of Jetpack Compose are composable functions — Kotlin functions annotated with @Composable. These composables define how UI elements should look and behave.

Unlike traditional UI construction with XML, composable functions let you describe your app’s UI programmatically by specifying its desired appearance and data dependencies. You don’t need to worry about the underlying process of element creation and attachment.

Why you should consider switching to Compose UI from XML?

In traditional Android development, UI development is handled using an imperative approach.

This means you explicitly tell the system what UI elements(views) to create and how to manipulate them at each step. You define the UI structure in XML layouts and then write code to find those views and update their properties (text, images, click listeners, etc.).

Jetpack Compose, on the other hand, takes a declarative approach.

You describe the desired UI state (what you want the UI to look like) in composable functions written in Kotlin. Compose handles the rendering logic itself, making your code more concise and easier to maintain.

Compare both approaches using the example of showing a text

Imperative (Traditional Views):

//in layout XML file
<TextView
    android:id="@+id/text_view"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!" />

//in Activity Kotlin class

val textView = findViewById<TextView>(R.id.text_view) 
textView.text = "Updated Text"

Declarative (Jetpack Compose):

Text(text = "Hello World!")

// Later, to update the text:
Text(text = "Updated Text")

How to create and define composable functions?

The setContent block defines the activity's layout where these composable functions are called. Importantly, composable functions can only be called from other composable functions, building a hierarchical UI structure.

setContent {
 Text(“Hello world!”)
}

To create a composable function, simply add the @Composable annotation to the function name.

For example, let’s look at a simple composable function called DisplayText:

@Composable
fun DisplayText() {
    Text(text = "Hello, World!")
}

In this example, the DisplayText function is marked as @Composable to indicate that it's a composable function. Inside the function, we use the built-in Text composable to display the text "Hello, World!". You can use this DisplayText function in your Jetpack Compose UI to show a text element.

There are many other built-in composable functions available, along with the ability to create your own custom composables for reusable UI components.

Behind the scenes, Jetpack Compose uses a Kotlin compiler plugin to transform these composable functions into the app’s UI elements. This allows you to focus on the what (the desired UI) rather than the how (the underlying implementation).

To learn more about the technical details and advanced features, visit the official documentation: https://developer.android.com/develop/ui/compose

If you found this introduction to Jetpack Compose helpful, consider giving this article a clap👏.

Stay tuned for Part 2: Composition vs. Inheritance in Jetpack Compose

Conquering Complexity: Composition vs. Inheritance in Jetpack Compose