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..!