Using Kotlin Multiplatform (KMP) to Share UI Logic: Compose vs Native SwiftUI

Introduction

In modern mobile app development, teams often need to build applications for both Android and iOS. Traditionally, this meant writing separate codebases using different technologies—Kotlin for Android and Swift for iOS.

This approach increases:

Development time
Maintenance cost
Code duplication

To solve this problem, developers are now using Kotlin Multiplatform (KMP).

KMP allows you to share code across platforms while still keeping native performance. But when it comes to UI, developers face an important decision:

Use Jetpack Compose Multiplatform (shared UI)
Use Native SwiftUI (platform-specific UI)

So the big question is:

Which approach is better?

In this article, we will explore both options in detail, including architecture, use cases, advantages, disadvantages, and real-world scenarios.

What is Kotlin Multiplatform (KMP)?

Kotlin Multiplatform is a technology that allows developers to write shared code in Kotlin and reuse it across platforms like Android, iOS, Web, and Desktop.

KMP = Write once (business logic), run everywhere with native UI

What Can Be Shared?

Business logic
Networking
Data models
Validation logic

Example

What is Jetpack Compose Multiplatform?

Jetpack Compose Multiplatform is a UI toolkit that allows developers to write UI code in Kotlin and share it across platforms.

Key Features

Declarative UI
Shared UI code
Faster development
Consistent design

Example

You can write a button UI once and use it on Android and iOS.

What is SwiftUI?

SwiftUI is Apple’s native UI framework for building iOS applications.

Key Features

Native performance
Deep iOS integration
Optimized for Apple ecosystem

Example

You design UI specifically for iOS using Swift language.

Architecture Options in KMP

When using KMP, there are two main approaches:

1. Shared UI (Compose Multiplatform)

UI + Logic shared
Single codebase

2. Shared Logic + Native UI (SwiftUI)

Logic shared
UI written separately

Compose vs SwiftUI

Feature	Compose Multiplatform	SwiftUI
UI Sharing	Yes	No
Code Reuse	High	Medium
Performance	Good	Excellent
Platform Feel	Moderate	Native
Development Speed	Fast	Moderate
Maintenance	Easier	More effort
Flexibility	High	High

Using Compose Multiplatform (Shared UI)

How It Works

UI written in Kotlin
Shared across Android and iOS
Rendered using platform-specific engines

Example Scenario

A startup building an MVP app:

Needs fast development
Limited resources

Compose helps:

Build once
Deploy everywhere

Advantages

Maximum code reuse
Faster development
Consistent UI across platforms

Disadvantages

Less native feel on iOS
Smaller ecosystem compared to SwiftUI
Learning curve for iOS teams

Using Native SwiftUI with KMP

How It Works

Business logic shared via KMP
UI built separately in SwiftUI

Example Scenario

A large enterprise app:

Needs high-quality iOS experience
Requires platform-specific features

SwiftUI helps:

Deliver native UI
Better user experience

Advantages

Native performance
Better iOS user experience
Full access to Apple APIs

Disadvantages

More code to maintain
Slower development
UI duplication

Real-World Use Cases

1. Startups and MVPs

Prefer Compose Multiplatform
Faster time-to-market

2. Enterprise Applications

Prefer SwiftUI + KMP
Focus on user experience

3. Cross-Platform Apps

Use shared UI for consistency

4. High-Performance Apps

Use native UI for better optimization

When Should You Choose Compose?

Choose Compose when:

You want maximum code sharing
You have a small team
You need faster delivery

When Should You Choose SwiftUI?

Choose SwiftUI when:

You want native experience
You have separate platform teams
You need deep iOS integration

Best Practices

1. Start with Shared Logic

Always share business logic first.

2. Evaluate UI Complexity

Simple UI → Compose
Complex UI → SwiftUI

3. Use Hybrid Approach

Combine both when needed.

4. Keep Code Modular

Separate UI and logic clearly.

5. Test Across Platforms

Ensure consistent behavior.

Common Mistakes to Avoid

Sharing too much UI unnecessarily
Ignoring platform guidelines
Overcomplicating architecture
Not testing on real devices

Conclusion

Kotlin Multiplatform is transforming how cross-platform apps are built.

When it comes to UI:

Compose Multiplatform offers speed and code reuse
SwiftUI offers native experience and performance

There is no one-size-fits-all solution.

The best approach depends on your project needs, team expertise, and user expectations.

In many cases, a hybrid approach—sharing logic and selectively sharing UI—provides the best balance.

By choosing the right strategy, you can build scalable, efficient, and high-quality mobile applications using Kotlin Multiplatform.