Posts Tagged ‘ComposeForiOS’
[KotlinConf2023] Compose Multiplatform on iOS: Sharing UIs Across Ecosystems with Sebastian Aigner and Nikita Lipsky
At KotlinConf’23, Sebastian Aigner (Developer Advocate at JetBrains) and Nikita Lipsky (Software Developer for Kotlin at JetBrains) presented an exciting overview of Compose Multiplatform, focusing on its then-Alpha support for iOS. Their session detailed how this JetBrains initiative enables developers to write their user interface once in Kotlin and deploy it across Android, iOS, desktop, and web, fostering significant code sharing and development efficiency. The official documentation for Compose Multiplatform offers further insights.
The presentation began by recapping the classic Kotlin Multiplatform (KMP) use case, which allows sharing of business logic while retaining access to platform-specific APIs. Compose Multiplatform builds upon this by providing a solution for sharing the UI layer itself, addressing scenarios where building and maintaining separate native UIs for each platform is not feasible due to time, resources, or the desire for rapid market entry. While the talk focused on iOS and Android, the speakers emphasized that Compose Multiplatform also supports desktop (stabilized in late 2021) and web targets.
Architecture and Jetpack Compose Foundations
A key point underscored by Sebastian and Nikita was that Compose Multiplatform is built upon Jetpack Compose, Google’s modern declarative UI toolkit for Android, which is 100% Kotlin. This means developers familiar with Jetpack Compose can leverage their existing knowledge and skills to build UIs for iOS and other platforms. The JetBrains team collaborates closely with Google, regularly upstreaming changes to the Jetpack Compose repositories.
Nikita Lipsky delved into the architecture, explaining that official Jetpack Compose itself is already a Kotlin Multiplatform project at its core, with its lowest levels defining Kotlin Multiplatform sources. The composable function concept is an extension to the Kotlin language requiring compiler support, and the entire Compose system is managed by the Compose Runtime. For iOS, Compose Multiplatform renders UI elements by drawing directly onto a CAPI (Canvas API) provided by Skiko, a graphics library that abstracts over Skia (for Android and desktop) and CoreGraphics (for iOS). This allows for consistent rendering across platforms.
Live Demos and iOS Integration
The session featured live demonstrations showcasing the capabilities of Compose Multiplatform on iOS. Sebastian Aigner walked through a sample application, highlighting how standard Jetpack Compose code for UI elements, state management (using remember), layouts (like Column), and modifiers can be shared and run on iOS simulators and devices. He demonstrated features like text input, button interactions, and even integration with iOS-specific functionalities like the share sheet, emphasizing the goal of seamless interoperability.
The speakers also discussed the importance of providing solid accessibility integrations and ensuring smooth performance, even on high-refresh-rate displays, which is an ongoing area of focus for the Kotlin/Native and Compose Multiplatform teams. Interoperability with existing iOS UI code (SwiftUI and UIKit) was also presented as a key feature, allowing for gradual adoption. Developers can embed Compose Multiplatform views within existing SwiftUI applications or, conversely, embed native iOS views within a Compose Multiplatform UI. This flexibility is crucial for teams looking to integrate Compose into their established projects incrementally.
Getting Started and Future Outlook
Sebastian and Nikita provided clear guidance on how developers can start experimenting with Compose Multiplatform for iOS. They pointed to project templates, sample applications available on the Compose Multiplatform GitHub repository (including to-do list apps and code viewers), and updated KMP production samples that now include branches with Compose-based UI implementations. The new memory manager in Kotlin/Native was also mentioned as a significant improvement, simplifying multi-threaded programming for all Kotlin targets, including iOS.
While acknowledging that the iOS target was in Alpha and some areas were still works in progress, the overall message was one of excitement and a call to action for the community. They encouraged developers to explore the technology, provide feedback, and contribute to its evolution. The vision is a future where developers can agree on a delightful way to write UIs for all their target platforms using Kotlin.