A Study of API Guidelines for Building Better Jetpack Compose Components

The Jetpack Compose ecosystem has grown exponentially in recent years, and it is now widely adopted for building production-level UIs in Android applications. We can now say that Jetpack Compose is the future of Android UI development.

One of the biggest advantages of Compose is its declarative approach. It allows developers to describe what the UI should display, while the framework handles how the UI should update when the underlying state changes. This model shifts the focus from imperative UI logic to a more intuitive and reactive way of thinking.

However, building reusable and scalable UI components requires more than just a grasp of declarative principles. It demands a thoughtful approach to API design. To guide developers, the Android team has published a comprehensive set of API guidelines. These best practices are not strict rules but are strongly recommended for creating components that are consistent, scalable, and intuitive for other developers to use.

In this article, you will explore the core principles outlined in these guidelines. We will examine the key recommendations for designing component APIs, from initial purpose and structure to parameter ordering and state management, to better understand how to build high-quality, production-ready composables.

The Philosophy: Clarity, Purpose, and Layering

Before writing a single line of code, the guidelines encourage developers to think critically about a component's purpose. A well-designed component should solve a single, well-defined problem. If a component attempts to do too much, it often leads to a complex and confusing API.

Consider a Button component that also tries to manage a "checked" state, like a checkbox.

// DON'T: Avoid multipurpose components
@Composable
fun Button(
    // Problem 1: A clickable rectangle
    onClick: () -> Unit = {},
    // Problem 2: A checkable component
    checked: Boolean = false,
    onCheckedChange: (Boolean) -> Unit,
) { /* ... */ }

This design conflates two distinct user interactions. The guidelines strongly recommend splitting this into two separate, single-purpose components: a Button for clicks and a ToggleButton for checkable states. This focus on a single responsibility makes each component's API simpler and its behavior more predictable.