Jetpack Compose

Jetpack Compose is Android’s modern toolkit for building native UIs with Kotlin. It simplifies UI development by using a declarative approach, meaning developers describe the UI in code and let the system handle the rest. Over the last few years, Jetpack Compose has become increasingly popular for building Android apps due to its flexibility, expressiveness, and seamless integration with other Android libraries.

In this blog post, we’ll dive deep into the Jetpack Compose core components, including the Compose Compiler Plugin, Compose Runtime, Compose UI Core, Compose UI Foundation, and Compose UI Material. Understanding these components is essential for building powerful and efficient Android applications with Jetpack Compose.

Jetpack Compose Core Components

Jetpack Compose core components include:

• Compose Compiler Plugin: Optimizes @Composable functions.
• Compose Runtime: Manages state and recomposition.
• Compose UI Core: Provides basic UI building blocks and modifiers.
• Compose UI Foundation: Adds common UI components and layouts.
• Compose UI Material: Delivers Material Design components.

These components work together to streamline UI development in Android.

Jetpack Compose Compiler Plugin

The Compose Compiler Plugin is responsible for transforming your composable functions into efficient, optimized code that can be executed by the Android platform.

Library Name: androidx.compose.compiler:compiler

Key Functions:

• Annotation Processing: The compiler recognizes @Composable functions and processes them accordingly.
• Code Transformation: It converts your composable functions into code that builds and manages the UI tree.
• Performance Optimization: By detecting changes in state, the compiler minimizes unnecessary recompositions to enhance efficiency.

How It Works:

When you mark a function with @Composable, the compiler plugin generates code that keeps track of the composable’s state and recomposition needs. This transformation allows Jetpack Compose to understand which parts of the UI need to be updated when data changes, ensuring efficient UI rendering.

Compose Runtime

The Compose Runtime is the engine that powers state management and recomposition in Jetpack Compose.

Library Name: androidx.compose.runtime:runtime

Core Responsibilities:

• State Management: It handles the state of composables and ensures that when data changes, only the affected parts of the UI are recomposed.
• Recomposition: The runtime efficiently updates the UI by re-rendering only what has changed, rather than the entire screen.
• UI Diffing: It compares the previous and current states to determine the minimal set of updates needed.

How It Works:

The runtime creates and maintains a tree structure of composables. When a composable’s state changes, the runtime selectively recomposes that part of the tree, making updates efficient and smooth.

Compose UI Core

The Compose UI Core library provides the essential building blocks for creating and arranging your UI components.

Library Name: androidx.compose.ui:ui

Key Elements:

• Layouts: Fundamental composables like Row, Column, Box, and ConstraintLayout help you organize UI elements.
• Modifiers: These allow you to adjust the appearance and behavior of composables. For example, you can apply padding, size adjustments, or click interactions using Modifier.padding() or Modifier.clickable().
• Drawing Tools: The core library supports custom graphics and drawing operations through APIs like Canvas.

How It Works:

Compose UI Core offers composables and modifiers that you can combine to create complex UIs. Modifiers are chainable, allowing you to apply multiple changes to a composable in a flexible way.

Compose UI Foundation

The Compose UI Foundation library builds on UI Core and provides commonly used UI elements and utilities for more interactive and polished interfaces.

Library Name: androidx.compose.foundation:foundation

Key Components:

• Text: Display text with customizable styles and formatting.
• Images: Render images from resources or assets.
• Specialized Layouts: Components like ConstraintLayout and BoxWithConstraints offer advanced layout options.
• Gesture Support: Built-in support for handling gestures like taps, drags, and swipes.

How It Works:

UI Foundation components are higher-level building blocks that simplify common UI tasks. For example, Text and Image are easy-to-use composables that can be styled and customized to suit your needs.

Compose UI Material

The Compose UI Material library brings Material Design components to Jetpack Compose, helping you build apps that follow Google’s design guidelines.

Library Name: androidx.compose.material3:material3

Key Components:

• Buttons: Standard Material buttons like Button, OutlinedButton, and IconButton.
• Cards: Card composables for grouping related content.
• Dialogs: Pre-built dialogs like AlertDialog for user interactions.
• Text Fields: Customizable input fields for user data.
• Theming: Built-in support for theming, allowing you to define colors, typography, and shapes.

How It Works:

Compose Material builds on the core and foundation libraries to provide ready-to-use components that align with Material Design principles. These components are customizable, allowing you to adapt them to your app’s branding.

Conclusion

Jetpack Compose revolutionizes Android UI development by providing a modern, declarative approach. Here’s a quick recap of the core components:

• Compose Compiler Plugin: Transforms @Composable functions into optimized code.
• Compose Runtime: Manages state and ensures efficient recomposition.
• Compose UI Core: Provides essential UI building blocks and modifiers.
• Compose UI Foundation: Adds common UI components and layout tools.
• Compose UI Material: Delivers Material Design components for a polished UI.

With Jetpack Compose, you can build flexible, maintainable, and high-performance UIs more easily than ever before. Whether you’re a beginner or an experienced developer, adopting Compose can significantly improve your Android development workflow.

happy UI composing..!

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..!

Jetpack Compose, introduced by Google, is a modern toolkit for building native UIs on Android. It aims to streamline UI development by eliminating the complexities of the old Android UI toolkit and providing a more declarative, functional approach. But before we dive into the world of Jetpack Compose, let’s first take a look at why it was introduced and how it solves problems that developers faced with the older UI toolkit.

Traditional Android UI Toolkit: Design Concepts

The traditional Android UI toolkit is built around a component-based hierarchical model. This design is deeply rooted in the concept of views as building blocks for user interfaces. Each view represents a visual element, such as a button, a text field, or an image.

• View: The base class for all UI components. Examples include TextView, ImageView, and Button.
• ViewGroup: A container for other views, such as LinearLayout, RelativeLayout, or ConstraintLayout.

                     LinearLayout (root)
                     /       |         \
          TextView         LinearLayout      RelativeLayout
          ["Welcome"]      (Horizontal)       /         \
                            /     \         ImageView   EditText
                      Button     Button     ["icon"]   ["Enter name"]
                      ["Submit"] ["Cancel"]

This tree-like structure allows developers to create complex interfaces by nesting views within containers.

Why This Design?

1. Flexibility: The component hierarchy provides flexibility in designing UIs by allowing developers to mix and match different views.
2. Reusability: Views can be reused across multiple parts of an application, reducing redundancy.
3. Separation of Concerns: Each view is responsible for its own behavior and appearance.

However, this design also introduces inefficiencies, especially with deeply nested hierarchies, which can slow down performance due to the time needed for layout calculations and rendering.

XML-Based Layouts

In traditional Android development, UIs are typically defined using XML files. These files describe the structure of the interface declaratively.

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello, World!" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click Me" />
</LinearLayout>

Advantages of XML Layouts

1. Separation of UI and Logic: XML keeps the UI separate from the Java/Kotlin code.
2. Easy to Visualize: Tools like Android Studio’s layout editor make it easy to visualize the layout.

Drawbacks

1. Verbosity: XML can become verbose, especially for complex UIs.
2. Rigid: Dynamic UI changes require programmatically altering views, leading to potential bugs and complexity.
3. Performance: Parsing XML and inflating views can be resource-intensive.

Understanding Custom Views

Custom views in the traditional Android UI toolkit allow developers to create unique UI components by extending the View class or ViewGroup class. This is particularly useful when the default widgets don’t meet the specific needs of your application.

Simples Steps to Create a Custom View

1. Extend the View Class: Create a class that extends View (for simple views) or ViewGroup (for compound views).
2. Override Lifecycle Methods: Implement methods like onMeasure, onDraw, and onLayout to define the view’s behavior.
3. Handle Custom Attributes: Define custom XML attributes to allow flexibility when using the view.

Let’s walk through an simple example of creating a custom CircleView that draws a circle on the screen.

Example: Creating a Custom CircleView

Step 1: Define the Custom View Class

class CircleView(context: Context, attrs: AttributeSet) : View(context, attrs) {

    private val paint = Paint().apply {
        color = Color.BLUE
        style = Paint.Style.FILL
    }

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)
        val radius = min(width, height) / 2f
        canvas.drawCircle(width / 2f, height / 2f, radius, paint)
    }
}

Step 2: Add the Custom View to XML

<com.softaai.customviews.CircleView
    android:layout_width="100dp"
    android:layout_height="100dp" />

Step 3: Customize in Code

val circleView: CircleView = findViewById(R.id.circleView)

Why Use Custom Views?

1. Unique UI Elements: When default widgets don’t meet your needs, custom views allow you to create tailored components.
2. Performance: Custom views can be optimized for specific use cases.

Drawbacks of Custom Views

1. Complexity: Writing custom views requires a solid understanding of Android graphics and layout.
2. Maintenance Overhead: Custom views can be harder to maintain and extend.

Technical Principles Behind Traditional UI Toolkit

Measure-Layout-Draw Cycle

The lifecycle of a view involves three key steps:

1. Measure: Calculate the dimensions of each view. Views need to know their size, which is defined in onMeasure.
2. Layout: Position the views within their parent containers. In a ViewGroup, onLayout positions the child views.
3. Draw: The onDraw method handles the visual rendering of the view and render the views on the screen.

Each step involves multiple passes through the view hierarchy, which can become inefficient for deep or complex layouts. While these principles ensure that views are flexible and reusable, they also come with certain drawbacks.

Drawbacks of the Traditional UI Toolkit

While the traditional UI toolkit is powerful, it has some notable limitations:

Complexity

• Boilerplate Code: XML files, findViewById, and handling view updates can lead to excessive boilerplate code.
• Manual State Management: Updating views manually whenever the state changes can result in complex and error-prone code.

Performance Issues

• Deep View Hierarchies: Rendering deeply nested views can degrade performance.
• Repetitive Rendering: The system may trigger unnecessary layout passes or redraw large portions of the view hierarchy, even for minor updates, leading to performance inefficiencies.

Maintainability

• Hard to Refactor: Large XML files and imperative codebases can be difficult to refactor and maintain.
• Limited Reusability: Creating and reusing custom views across different projects can be cumbersome.

There are many challenges with the old UI toolkit. I’ve highlighted a few of them here. These challenges led to the development of a modern approach to building UIs in Android: Jetpack Compose.

The Rise of Jetpack Compose: Modern UI Toolkit

Jetpack Compose is a declarative UI toolkit that allows Android developers to create UIs using Kotlin programming language. Unlike traditional XML-based layouts, Jetpack Compose defines the UI within Kotlin code, making it easier to work with and more dynamic. By leveraging Kotlin’s power, Jetpack Compose provides a more modern, flexible, and efficient way to develop Android UIs.

Now, let’s take a deep dive into how Jetpack Compose overcomes the drawbacks of traditional Android UI toolkits and why it’s quickly becoming the go-to choice for Android development.

1. Declarative UI: Simplicity and Flexibility

One of the key principles behind Jetpack Compose is the declarative approach to UI development. In traditional Android development, you would have to describe the layout of UI elements and the logic separately (in XML and Java/Kotlin code). In Jetpack Compose, everything is done inside the Kotlin code, making it much simpler and more cohesive.

With Jetpack Compose, you describe the UI’s appearance by defining composable functions, which are functions that define how UI elements should look based on the app’s current state. Here’s a simple example of a button in Jetpack Compose.

@Composable
fun GreetingButton(onClick: () -> Unit) {
    Button(onClick = onClick) {
        Text("Click Me!")
    }
}

The declarative nature allows for UI elements to be modified easily by changing the state, reducing the complexity of managing UI components manually.

2. No More findViewById or View Binding

One of the pain points of traditional Android UI development was the need to reference views using findViewById() or even use View Binding. These approaches added complexity and could result in null pointer exceptions or repetitive code.

With Jetpack Compose, there is no need for findViewById() because all UI elements are created directly in Kotlin code. Instead of manually referencing views, you define UI components using composables. Additionally, since Jetpack Compose uses state management, the UI automatically updates when the state changes, so there’s no need for manual intervention.

3. Less Boilerplate Code

Jetpack Compose significantly reduces the need for boilerplate code. In traditional XML-based development, a UI element like a button might require multiple lines of code across different files. In contrast, Jetpack Compose reduces it to just a few lines of Kotlin code, which leads to cleaner and more maintainable code.

For instance, creating a TextField in Jetpack Compose is extremely simple:

@Composable
fun SimpleTextField() {
    var text by remember { mutableStateOf("") }
    TextField(value = text, onValueChange = { text = it })
}

As you can see, there’s no need for complex listeners or setters—everything is managed directly within the composable function.

4. Powerful State Management

State management is an essential aspect of building dynamic UIs. In traditional Android UI toolkits, managing state across different views could be cumbersome. Developers had to rely on LiveData, ViewModels, or other complex state management tools to handle UI updates.

Jetpack Compose, however, handles state seamlessly. It allows developers to use state in a much more intuitive way, with mutableStateOf and remember helping to store and manage state directly within composables. When the state changes, the UI automatically recomposes to reflect the new state, and saving developers from having to manually refresh views.

@Composable
fun Counter() {
    var count by remember { mutableStateOf(0) }
    Button(onClick = { count++ }) {
        Text("Count: $count")
    }
}

This simple, dynamic approach to state management is one of the core reasons why Jetpack Compose is considered a powerful modern toolkit.

5. Customizable and Reusable Components

Jetpack Compose encourages the creation of reusable UI components. Composables can be easily customized and combined to create complex UIs without sacrificing maintainability. In traditional Android development, developers often need to write custom views or use third-party libraries to achieve flexibility in their layouts.

In Jetpack Compose, developers can create custom UI components effortlessly by combining smaller composables and applying modifiers to adjust their behavior and appearance.

@Composable
fun CustomCard(content: @Composable () -> Unit) {
    Card(modifier = Modifier.padding(16.dp), elevation = 8.dp) {
        content()
    }
}

This flexibility allows for more scalable and maintainable UI code, which is particularly beneficial as the app grows.

Core Features of Jetpack Compose

1. Declarative UI: Build UIs by defining composables, leading to a cleaner and more intuitive way of designing apps.
2. State Management: Automatic UI recomposition based on state changes, reducing manual updates.
3. Reusable Components: Easy to create modular, reusable, and customizable UI elements.
4. Kotlin Integration: Leverages Kotlin’s features for more concise, readable, and maintainable code.
5. No XML: Eliminates the need for XML layouts, improving development speed and reducing errors.

Conclusion

Jetpack Compose represents a major shift in Android UI development by solving many issues that developers faced with the old Android UI toolkit. By adopting a declarative, state-driven approach, it simplifies UI creation, reduces boilerplate code, and improves the overall development experience. With its powerful features and seamless integration into the Android ecosystem, Jetpack Compose is the future of Android app development.

As you explore Compose further, you’ll discover how it can be used to create complex and dynamic UIs with less code and more efficiency. So, if you’re still stuck with the old XML-based UI, it’s time to embrace the future with Jetpack Compose!

happy UI composing..!