[KotlinConf2024] Compose Multiplatform Evolves on iOS and Beyond
At KotlinConf2024, Sebastian Aigner, a JetBrains developer advocate, unveiled advancements in Compose Multiplatform, now in beta for iOS and alpha for web. Extending beyond business logic, Compose enables shared UI across platforms, integrating native capabilities. Sebastian showcased new common APIs—previews, resources, lifecycle, navigation, and UI testing—alongside iOS-specific enhancements like accessibility and scroll physics. Through live demos, he demonstrated how these features simplify cross-platform development, inviting developers to shape Compose’s future with feedback.
A Year of Progress for Compose Multiplatform
Since its debut at KotlinConf2023, Compose Multiplatform has matured significantly. Sebastian highlighted its role in sharing UI code, complementing Kotlin Multiplatform’s business logic sharing. On Android, it leverages Jetpack Compose; on desktop, it powers JetBrains Toolbox; and on iOS, it reached beta status at KotlinConf2024. The web target hit alpha, broadening its reach. Progress spans accessibility, navigation, text input, and scroll physics, with most features now stable or experimental, ready for developers to adopt and refine through real-world use.
iOS-Specific Enhancements
Compose Multiplatform on iOS now feels native, thanks to revamped scroll physics mirroring iOS’s overscroll and spring effects. Sebastian demonstrated accessibility improvements, with components supporting VoiceOver and gesture navigation out of the box, provided content descriptions are added. Interop with SwiftUI allows popups to span the screen, and window insets APIs handle notches and dynamic islands, ensuring full-screen rendering. These enhancements make iOS apps built with Compose visually and functionally indistinguishable from native counterparts, enhancing user experience.
Common Resources for Seamless UI
The new common resources API simplifies asset management. Sebastian showed how to add drawables and strings in a composeResources directory, accessed via a type-safe res object. In a demo, he added a banner image and a localized conference description, with Fleet auto-generating accessors. Support for multimodule resources and translations (e.g., German dark mode) ensures flexibility. This API, familiar from Android, reduces boilerplate, letting developers focus on crafting polished, platform-agnostic UIs with minimal effort.
Lifecycle and View Models in Common Code
Compose Multiplatform now supports common lifecycle and view model APIs, enabling robust app architecture. Sebastian demonstrated a lifecycle logger tracking states like onCreate and onPause, with collectAsStateWithLifecycle ensuring efficient flow collection. In a view model demo, he outsourced mood-tracking logic, using a factory function to instantiate it. Integration with Koin for dependency injection and lifecycle-aware state collection streamlines development, making MVVM patterns viable across platforms without platform-specific workarounds.
Navigation for Cross-Platform Apps
Navigation, a cornerstone of multiplatform apps, is now available via a Jetpack Navigation-inspired API. Sebastian built a demo app with a fruit list and detail pages, using a NavHost and NavController for stack-based navigation. Features like window insets padding, animated transitions, and rememberSaveable for state persistence ensure a native feel. Type-safe routing with Kotlinx.serialization is in development, reducing errors. This API, while optional, simplifies porting Android navigation logic to iOS and beyond, enhancing developer productivity.
UI Testing and Community Feedback
A new common UI testing API allows writing tests once for all platforms. Sebastian showed a test verifying a composable’s text content, executed across targets. This reduces testing overhead, ensuring consistent behavior. He urged developers to try these features, citing the Compose Multiplatform portal (jb.compose) for documentation. Feedback via the Kotlin Slack and issue tracker is vital, as community input drives stabilization. With support for features like strong skipping mode and shared element transitions, Compose continues to evolve dynamically.