Flutter vs. Kotlin Multiplatform (KMP): A Deep Dive

The realm of cross-platform app development has witnessed a surge in recent years, with Flutter and Kotlin Multiplatform (KMP) emerging as prominent contenders. Each framework offers unique strengths and caters to different project requirements. This comprehensive comparison delves into the core features, performance, development experience, and use cases of both frameworks to assist you in making an informed decision for your next app.

Understanding Flutter and Kotlin Multiplatform

 

Flutter

Flutter, a UI toolkit developed by Google, enables the creation of natively compiled applications for mobile, web, and desktop from a single codebase. It employs the Dart programming language and offers a rich set of pre-built widgets for rapid UI development. Flutter’s architecture, based on the Impeller graphics engine (Before Impeller, Skia graphic engine was implemented), provides high performance and visually appealing applications.

Key Features of Flutter:

• Single Codebase: Write once, run anywhere approach for multiple platforms.
• Rich Widget Library: Pre-built customizable widgets for a consistent look and feel.
• Hot Reload: Instant feedback during development for quick iterations.
• High Performance: Thanks to the Impeller graphics engine and ahead-of-time (AOT) compilation.
• Extensive Documentation: Comprehensive resources for learning and troubleshooting.

Advantages of Flutter:

• Consistency: Ensures a uniform user experience across different platforms.
• Efficiency: Reduces the amount of code developers need to write.
• Developer Productivity: Tools like hot reload significantly boost productivity.

Disadvantages of Flutter:

• Platform-Specific Features: May require additional work to access certain native features.
• App Size: Flutter apps can be larger due to the inclusion of the Dart runtime and additional libraries.

Kotlin Multiplatform (KMP)

Kotlin Multiplatform (KMP), developed by JetBrains, is a technology that allows you to share business logic across different platforms, including iOS, Android, web, and desktop. Unlike Flutter, KMP focuses on code sharing rather than a unified UI framework. It leverages Kotlin’s ability to compile to different target platforms, enabling you to create platform-specific UIs while sharing core business logic.

Key Features of Kotlin Multiplatform:

• Code Sharing: Share business logic across multiple platforms while keeping platform-specific UIs.
• Native Performance: Achieve near-native performance through direct platform API access.
• Flexibility: Allows using native UI components for a truly native look and feel.
• Kotlin Language: Utilizes Kotlin, a modern language with strong community support.
• Gradual Adoption: Can be introduced incrementally into existing projects.

Advantages of KMP:

• Native Experience: Offers the ability to use native UI components for each platform.
• Reusability: Promotes code reuse, reducing duplication and maintenance efforts.
• Integration: Seamlessly integrates with existing projects and platforms.

Disadvantages of KMP:

• Complexity: Requires managing separate UIs for each platform.
• Learning Curve: Steeper learning curve due to the need for platform-specific knowledge.

Key Differences

 

Performance Showdown

Both Flutter and Kotlin Multiplatform (KMP) prioritize performance, but their approaches differ.

Flutter Performance

• Rendering Engine: Flutter’s Impeller graphics engine ensures efficient rendering and smooth animations.
• Ahead-of-Time (AOT) Compilation: Compiles to native code for enhanced performance.
• Platform Channels: Facilitates interaction with native code, though with some overhead.
• Hot Reload: Speeds up development but may introduce some performance overhead during runtime.

Examples of Flutter’s Performance:

• YouTube Create (Beta): Utilizes Flutter to provide a seamless and high-performance video editing experience. The app delivers a consistent and responsive user interface across platforms, ensuring smooth video editing and creative features.
• Reflectly: A journaling app that takes advantage of Flutter’s smooth animations and efficient rendering.

Kotlin Multiplatform Performance

• Native Compilation: Compiles to platform-specific code for optimal performance.
• Direct Platform Interaction: Allows direct access to platform APIs, minimizing performance overhead.
• UI Performance: Dependent on the chosen native UI framework, enabling platform-specific optimizations.
• Potential for Optimization: Offers opportunities for performance tuning through native code integration and careful structuring.

Examples of KMP’s Performance:

• PlanGrid: A construction productivity software that uses KMP for sharing business logic across mobile platforms.
• KeePassXC: A password manager that leverages KMP for cross-platform code sharing while maintaining platform-specific UIs.

In general, both frameworks can deliver high-performance apps. Flutter often excels in UI smoothness and animations, while KMP can be advantageous for computationally intensive tasks or those requiring tight integration with platform-specific features.

UI/UX Development

UI/UX is a critical aspect of any app’s success. Let’s compare how Flutter and  Kotlin Multiplatform (KMP) approach UI development:

Flutter:

• Rich Widget Set: Pre-built widgets for rapid UI development and visual consistency.
• Customizable Widgets: Allows tailored designs while maintaining performance.
• Visual Consistency: Strong focus on consistent UI across all platforms.
• Limitations: May face challenges in achieving platform-specific UI nuances.

Flutter in Action:

• eBay Motors: Uses Flutter to create a visually appealing and consistent UI for buying and selling cars.
• Toyota: Leverages Flutter to deliver a user-friendly and engaging experience for its customers, showcasing Flutter’s capability to handle complex UIs and animations.

Kotlin Multiplatform:

• Native UI Components: Leverages native components for each platform for a truly native experience.
• Full Customization: Provides full control over platform-specific UI adaptations.
• Separate UI Development: Requires development of distinct UIs for each platform, which can be time-consuming.

KMP in Action:

• Expedia: Utilizes KMP to share business logic while maintaining native UIs for a seamless user experience.
• Netflix: Uses KMP for sharing code across platforms to ensure high performance and native look and feel.

Flutter excels in creating visually appealing and consistent UIs across platforms. KMP, on the other hand, offers greater flexibility for platform-specific UI adaptations but requires more development effort.

Developer Experience

The developer experience encompasses factors such as the learning curve, tooling, and community support.

Flutter:

• Learning Curve: Relatively easy due to Dart’s simplicity and extensive documentation.
• Ecosystem: Rich ecosystem of plugins and packages for various functionalities.
• Hot Reload: Facilitates rapid development and testing.
• Community: Large and active community providing ample resources and support.

Developer Testimonials:

• Nubank Developers: Many developers praise Flutter for its ease of use and the ability to iterate on UI designs quickly.
• LG: The Flutter rewrite launched twice as fast as LG’s original app, consumed less runtime memory, and felt more responsive and playful to use.

Kotlin Multiplatform:

• Knowledge Requirement: Requires understanding of Kotlin and platform-specific development for iOS and Android.
• Ecosystem: Smaller but growing, with increasing support from the community.
• Learning Curve: Steeper, especially for complex projects involving multiple platforms.
• Tooling: Gradually improving with more tools and libraries becoming available.

Developer Testimonials:

• Expedia Developers: Highlight the benefits of code sharing and the ability to write platform-specific features when needed.
• PlanGrid Developers: Value KMP for enabling code reuse across mobile platforms while allowing native UI development.

In summary, Flutter generally offers a smoother developer experience due to its comprehensive documentation and larger community, but developers still need a good grasp of platform-specific details. KMP, while powerful and enabling convenient sharing of business logic, requires a deeper understanding of multiple platforms and has a steeper learning curve.

Cost and Time-to-Market

Cost and time-to-market are crucial considerations for any project.

Flutter:

• Development Speed: Faster development due to hot reload and pre-built widgets.
• Cost Savings: Cost Savings: Potential for cost savings through extensive code sharing, a single codebase for multiple platforms, a single development team, and maintenance of one codebase only.
• Complex UI Customizations: May require additional effort for platform-specific customizations.

Case Study:

• Alibaba: Uses Flutter to quickly iterate and deploy features across its e-commerce platforms, reducing time-to-market and development costs.

Kotlin Multiplatform:

• Initial Setup: Slower initial setup due to separate UI development for each platform.
• Long-term Savings: Potential long-term cost savings through shared business logic and performance optimizations.
• Complex Projects: Can be more efficient for complex projects requiring extensive platform-specific features.

Case Study:

• Square: Utilizes KMP to maintain a single codebase for business logic, reducing development costs and improving maintainability.

Flutter often has a shorter time-to-market due to its rapid development capabilities. KMP can be more cost-effective in the long run, especially for complex projects with extensive platform-specific requirements.

When to Choose Flutter or KMP

 

Choose Flutter if:

• Rapid development and time-to-market are priorities.
• Consistent UI across platforms is needed.
• The team is comfortable with Dart and reactive programming.

Ideal Projects for Flutter:

• Startups: Looking to quickly launch an MVP across multiple platforms.
• Consumer Apps: Requiring a visually appealing and consistent UI.

Choose Kotlin Multiplatform if:

• Native performance and platform-specific features are priorities.
• There is an existing codebase to leverage.
• The team has experience with Kotlin and native development.

Ideal Projects for KMP:

• Enterprise Apps: Needing robust performance and integration with platform-specific features.
• Complex Applications: Involving heavy computations or data processing.

Ultimately, the best choice depends on your project’s specific needs, team expertise, and long-term goals.

Real-world Performance Considerations

While benchmarks can provide valuable insights, real-world performance often depends on various factors:

App Complexity

• Complex UIs: Flutter excels with complex UIs and animations due to its powerful rendering engine.
• Heavy Computations: KMP might have a slight edge in scenarios requiring heavy computations or data processing due to its direct access to native capabilities.

Platform-Specific Optimizations

• Flutter: May require additional work for optimizing platform-specific features.
• KMP: Direct platform interactions can optimize performance without significant overhead.

Developer Expertise

• Flutter: Easier for developers with experience in Dart and reactive programming.
• KMP: Best suited for developers familiar with Kotlin and platform-specific development.

Third-Party Libraries

• Flutter: A rich ecosystem of third-party libraries facilitates rapid development.
• KMP: A growing ecosystem, with more libraries becoming available to enhance functionality and performance.

Conclusion

Choosing between Flutter and Kotlin Multiplatform requires careful consideration of your app’s specific needs and long-term goals. Flutter shines in providing a unified development experience with its rich set of pre-built widgets and rapid development capabilities, making it ideal for projects where a consistent and visually appealing UI across platforms is paramount. Its single codebase approach can accelerate development and streamline maintenance, especially for teams focused on quick iterations and high UI consistency.

On the other hand, Kotlin Multiplatform excels in scenarios where business logic needs to be shared across platforms while allowing for native UI development. It provides flexibility for integrating platform-specific features and optimizing performance through direct access to native APIs. This makes KMP particularly suitable for applications with complex business logic or those that require fine-tuned performance and close integration with platform-specific functionalities.

Ultimately, the choice between Flutter and KMP should be guided by factors such as your team’s expertise, project complexity, performance requirements, and the need for platform-specific customizations. Both frameworks offer powerful capabilities, but aligning their strengths with your project’s goals will help you achieve the best results.

At Reactree, we specialize in leveraging the latest technologies, including Flutter and Kotlin Multiplatform, to deliver high-quality, performance-driven applications tailored to your needs. Whether you’re looking to develop a cross-platform app with Flutter’s rapid UI capabilities or harness the power of Kotlin Multiplatform for complex business logic, our team is here to help. Contact us today to discuss your project and see how we can turn your vision into reality!