In recent years, cross-platform development has gained significant momentum as developers seek to create apps that run on multiple platforms with a single codebase. Two major players in this space are Kotlin Multiplatform (KMP) and Flutter, both offering unique benefits and approaches to solving the cross-platform dilemma. But which one should you choose for your next project?
In this blog, we’ll explore the key differences between Kotlin Multiplatform (KMP) and Flutter, comparing their architecture, performance, development experience, and suitability for different use cases.
1. What Is Kotlin Multiplatform (KMP)?
Kotlin Multiplatform (KMP) is a feature of Kotlin that allows you to write common code that runs on multiple platforms, including Android, iOS, desktop, and web. KMP enables code sharing across different platforms while still allowing you to write platform-specific code when necessary.
Key Features of KMP:
- Shared Logic: You can write business logic, networking, and other shared code in Kotlin and reuse it across platforms.
- Native UI: UI code is written separately for each platform, which gives developers full control over the look and feel of their app on Android, iOS, etc.
- Flexible Architecture: KMP doesn’t force you to follow a specific architecture. You can integrate it into existing apps or start new projects using KMP.
2. What Is Flutter?
Flutter is Google’s open-source UI software development kit (SDK) that allows you to build natively compiled applications for mobile, web, and desktop from a single codebase. It uses Dart as its programming language and provides a complete framework for developing cross-platform apps with a consistent UI.
Key Features of Flutter:
- Single Codebase for UI: You can create a single user interface for multiple platforms (Android, iOS, web, desktop) using Flutter’s widget system.
- Custom Rendering Engine: Flutter uses its own rendering engine, which allows for pixel-perfect UI across platforms, eliminating the need to write platform-specific UI code.
- Hot Reload: One of the standout features of Flutter is its “hot reload,” which allows developers to see the results of their code changes instantly without restarting the entire app.
3. Architecture and Development Approach
Kotlin Multiplatform (KMP): Native-First Approach
KMP focuses on sharing business logic while keeping the UI and platform-specific code separate. You write the core functionality (networking, caching, data models, etc.) in Kotlin, which is shared across platforms. However, the UI code for Android and iOS must be written natively (in Kotlin for Android and Swift for iOS).
- Native UI: With KMP, you get the flexibility to write native UIs for each platform, resulting in better adherence to platform conventions and user experience.
- Code Sharing: While KMP excels in logic/code sharing, it doesn’t enforce shared UI, making it ideal for projects that prioritize a native look and feel.
Flutter: UI-First Approach
Flutter takes a UI-centric approach, where both the business logic and UI are written in a single codebase using Dart. Flutter handles rendering using its own engine, bypassing native components, which allows for uniform UI across platforms.
- Unified UI: Flutter’s widget system allows developers to build custom UIs that look the same across platforms, making it ideal for apps that need a consistent experience.
- Less Platform-Specific Code: Since Flutter manages most of the platform differences internally, there is little need for platform-specific code compared to KMP.
4. Performance Comparison
Kotlin Multiplatform (KMP) Performance:
KMP apps utilize native UI and native code execution. This means that KMP-based apps run at native speed and performance, especially for platform-specific functionalities like animations, camera access, or GPS usage.
- Native Performance: Since KMP uses native code, performance is usually on par with fully native apps.
- Platform-Specific Optimization: You can optimize performance separately for Android and iOS if needed.
Flutter Performance:
Flutter uses the Dart language and compiles to native machine code for mobile, desktop, and web apps. It renders the UI via Skia, a powerful 2D rendering engine, which allows for high-performance, pixel-perfect UI rendering.
- Smooth Animations: Flutter’s rendering engine handles complex animations and transitions smoothly at 60fps or higher.
- Unified Performance: Since Flutter handles most of the platform-specific operations internally, performance is relatively consistent across platforms.
5. Development Experience
Kotlin Multiplatform (KMP):
- Language Familiarity: If you’re already an Android developer, you’re likely familiar with Kotlin, which makes the learning curve for KMP relatively shallow.
- Tooling Support: KMP is fully integrated with Android Studio, and with IntelliJ IDEA for cross-platform development. However, the tooling and ecosystem for KMP are still evolving, especially for iOS development.
- Flexibility: KMP allows you to gradually adopt a cross-platform approach. You can share as much or as little code as you like and maintain full control over the native parts of your app.
Flutter:
- Quick Setup: Flutter provides a fast setup process, and its “hot reload” feature makes it easy to iterate quickly on your designs and logic.
- Single Language: You’ll need to learn Dart, which might be a learning curve if you come from a Kotlin/Java background. However, Dart is fairly easy to pick up.
- Rich Ecosystem: Flutter has a vast ecosystem of widgets and libraries that allow you to build complex UIs quickly.
- Visual Design: Flutter is great for creating highly custom UIs and animations, and its widget system is well-suited for rapid development.
6. Use Cases and Suitability
When to Use Kotlin Multiplatform (KMP):
- Existing Native Codebases: If you already have native Android or iOS codebases and want to share common logic without rewriting the entire UI, KMP is an ideal solution.
- Platform-Specific UIs: KMP is great if you need to deliver the best possible native UI for each platform, adhering to their design standards.
- Gradual Adoption: KMP can be introduced gradually, allowing you to share business logic while keeping platform-specific code intact.
When to Use Flutter:
- Consistency Across Platforms: If you need a single, uniform UI across platforms, Flutter is a better choice as it handles all platform-specific differences internally.
- Rapid Prototyping: Flutter’s hot reload and comprehensive widget system make it ideal for fast prototyping and building MVPs.
- Custom UI Requirements: Flutter excels in apps that require custom UI designs and highly dynamic interfaces, such as animations and transitions.
7. Community and Ecosystem
Kotlin Multiplatform (KMP):
- Growing Ecosystem: KMP’s ecosystem is growing, with more libraries supporting multiplatform projects, though it’s still not as mature as Flutter’s.
- Strong Kotlin Community: Backed by JetBrains and Google, Kotlin has a strong and expanding community, especially within the Android development sphere.
Flutter:
- Vibrant Ecosystem: Flutter has a rich ecosystem of third-party packages, and Google actively supports and maintains the framework. The community around Flutter is large, with extensive tutorials, packages, and resources.
- Cross-Platform Beyond Mobile: Flutter is rapidly expanding to web, desktop, and embedded devices, making it a versatile tool for multi-platform apps.