If you’re like me, you’ve probably spent countless hours grappling with Android’s traditional UI toolkit. The constant juggling of XML layout files, view hierarchies, and state management can quickly become tedious. Thankfully, Google introduced Jetpack Compose, a modern toolkit that simplifies UI development by enabling you to write your interface in pure Kotlin. In this blog, we’ll explore the basics of Jetpack Compose, break down its core concepts, and walk through a simple example to help you get started. So, let’s dive in!

What is Jetpack Compose?

Before understanding what Jetpack Compose is, it’s very important to first grasp the challenges of Android’s traditional UI toolkit.

Challenges with the Old Android UI Toolkit

View.java Complexity

At the heart of the traditional UI toolkit lies View.java. This class is massive, with thousands of lines of code that make it cumbersome to maintain and extend. As our application scales, managing such a monolithic structure becomes increasingly difficult. The lack of modularity in the View class often leads to:

• Hard-to-track bugs.
• Performance bottlenecks.
• Difficulty in introducing new UI features.

Custom Views are Hard to Implement

Creating custom views in the old UI toolkit involves writing extensive code. Developers often need to override multiple methods, manage intricate drawing logic, and handle lifecycle intricacies. This makes custom view development time-consuming and error-prone.

Imperative Programming Complexity

The old toolkit relies on imperative programming, where developers describe how to achieve a specific outcome. This approach leads to code that’s harder to read, maintain, and debug, especially when managing complex UI states.

In contrast, declarative programming focuses on describing what the UI should look like based on the current state. This shift simplifies code and enhances readability.

Unclear Source of Truth

In traditional Android development, it’s often unclear:

• Where the source of truth for the UI state resides.
• Who owns the data.
• Who updates the UI when the data changes.

This ambiguity can lead to tightly coupled code, making maintenance and debugging challenging.

Enter Jetpack Compose: A Declarative UI Framework

Jetpack Compose, introduced by Google, represents a paradigm shift in Android UI development. It leverages declarative programming to simplify building and maintaining UIs. Let’s explore the core principles and advantages of Jetpack Compose.

Composables: The Building Blocks

In Jetpack Compose, you build your UI using composables. A composable is simply a function annotated with @Composable. These functions describe how the UI should look based on the current state.

@Composable
fun Greeting(name: String) {
    Text(text = "Hello, $name!")
}

Kotlin-Centric

Jetpack Compose is fully written in Kotlin, allowing developers to utilize all of Kotlin’s powerful features, such as:

• Coroutines for asynchronous programming.
• Extension functions for cleaner code.
• Lambdas for concise event handling.

UI as a Function of Data

In Compose, your UI is a direct function of your data. This means that whenever the data changes, the UI updates automatically. There’s no need to manually update views, reducing boilerplate and potential for bugs.

Simplified Entry Point: setContent { }

We define our composables within the setContent { } block, which serves as the entry point for our UI.

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            Greeting(name = "Android")
        }
    }
}

Separation of Concerns

Jetpack Compose gives you control over where to draw the line between business logic and UI code. This flexibility allows for cleaner architecture and better code organization. You can keep your business logic separate from your composables, making your codebase more maintainable.

Composition Over Inheritance

Compose promotes composition instead of inheritance. You can build complex UIs by combining smaller composables rather than extending large, monolithic classes. This leads to:

• Greater modularity.
• Easier testing.
• Reusable UI components.

Unidirectional Data Flow

Jetpack Compose adheres to unidirectional data flow. You pass data down to composables via function parameters and propagate events back up using callbacks.

@Composable
fun Counter(count: Int, onIncrement: () -> Unit) {
    Button(onClick = onIncrement) {
        Text("Count: $count")
    }
}

This ensures a clear, predictable flow of data and events, making the UI easier to reason about.

Recomposition for State Management

Jetpack Compose uses recomposition to update the UI when the state changes. When data changes, Compose re-executes the affected composables, efficiently updating only the parts of the UI that need to change.

No Annotation Processing

Unlike the old toolkit, Compose doesn’t rely on annotation processors. Instead, it uses the Compose Compiler Plugin to process composable functions, leading to faster builds and better performance.

Why Use Jetpack Compose?

Here’s a quick breakdown of what makes Jetpack Compose special:

• Declarative: We describe what the UI should look like based on the app’s state.
• Kotlin-based: No more juggling between Kotlin and XML; everything is in one language.
• Reactive: UI updates automatically when the underlying state changes.
• Simplified: No need for complex view hierarchies or findViewById().
• Faster Development: Live previews and hot reloads speed up the development cycle.
• State Management: Built-in tools make state handling simpler and more intuitive.
• Easy Integration: It coexists nicely with existing Views and XML, so migration is gradual.

A Simple Example: “Hello, Jetpack Compose!”

Let’s start with a basic example to display a simple “Hello, Jetpack Compose!” text on the screen. This will give us a taste of how declarative UI works in Compose.

Add Dependencies

To use Jetpack Compose, ensure your project is set up with the required dependencies. Add the following to your build.gradle (Module) file:

android {
    // Enable Jetpack Compose
    buildFeatures {
        compose true
    }
    
    composeOptions {
        kotlinCompilerExtensionVersion '1.5.1' // Check for the latest version
    }
}

dependencies {
    implementation 'androidx.compose.ui:ui:1.5.1'
    implementation 'androidx.compose.material:material:1.5.1'
    implementation 'androidx.compose.ui:ui-tooling-preview:1.5.1'
    debugImplementation 'androidx.compose.ui:ui-tooling:1.5.1'
}

Now, let’s create our first composable function!

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.material.MaterialTheme
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.tooling.preview.Preview

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // Enable edge-to-edge UI
        enableEdgeToEdge()
        setContent {
            JetpackUIDemoComposerTheme {
                Scaffold(modifier = Modifier.fillMaxSize()) { innerPadding ->
                    Greeting(
                        name = "Jetpack UI Demo Composer",
                        modifier = Modifier.padding(innerPadding)
                    )
                }
            }
        }
    }
}

@Composable
fun Greeting(name: String, modifier: Modifier = Modifier) {
    Text(
        text = "Hello $name!",
        modifier = modifier
    )
}

@Preview(showBackground = true)
@Composable
fun GreetingPreview() {
    JetpackUIDemoComposerTheme {
        Greeting("Jetpack UI Demo Composer")
    }
}

Here,

ComponentActivity and setContent:

• Instead of using setContentView and inflating XML layouts, we use setContent to define the UI in Kotlin code.

@Composable Annotation:

• This annotation marks a function as composable, meaning it can define UI components.
• Greeting(name: String) is a composable function that takes a name parameter and displays it.

Text Composable:

• The Text composable is a simple way to display text on the screen.

@Preview Annotation:

• This annotation lets us preview the UI directly in Android Studio without running the app.

MaterialTheme:

• It applies Material Design theming to our app, ensuring a modern look and feel.

Conclusion

Jetpack Compose makes UI development for Android simpler, more intuitive, and more enjoyable. By writing declarative composable functions in pure Kotlin, we eliminate the need for XML and reduce boilerplate code. Whether you’re building a new app or modernizing an existing one, Jetpack Compose is worth exploring.

I hope this introduction has given you a solid starting point. As you dive deeper, in upcomming blogs, you’ll discover even more powerful features like animations, themes, and advanced state management.

happy UI composing..!