Flutter vs. Kotlin Multiplatform: Key Factors to Consider for Your App

Not so long ago, everyone was talking about Flutter as the newest and best option for developing your cross-platform project. Today, Kotlin Multiplatform (KMP) has emerged as a strong competitor and has stolen much of the attention. So, does the rise of KMP mean you should abandon your Flutter project? Far from it! Flutter is still in a strong position. Both technologies have their pros and cons and are better suited for some projects than others.

However, it can be hard not to get lost in the shuffle. We are here to help you figure out which technology is best for YOUR project based on your resources and business goals. 

Flutter vs. Kotlin Multiplatform in a nutshell

Kotlin Multiplatform and Flutter are both relatively new development tools. Both aim to create cross-platform digital products, but they take quite different approaches to this goal.

Let’s  explain this in a simple way:

Flutter uses its own UI rendering tool to create what you see on the screen – a Flutter engine. This means that Flutter draws everything itself, ensuring that the look and feel are the same on every device, regardless of the platform.

KMP, on the other hand, uses the built-in tools of each platform (such as iOS or Android) to build the visual parts of the app. This approach focuses on growing and handling more tasks easily, making it scalable. Also, It ensures that the app looks and behaves exactly as expected on each platform, following its specific guidelines.

Therefore, we can say that Kotlin is an extension of native applications, while Flutter is their replacement. What many people don’t know is that both technologies are native in terms of code, but follow a different philosophy – we’ll discuss this in detail later in this article. 

In the meantime, here is a basic feature comparison chart between Flutter and Kotlin Multiplatform.

Feature	Flutter	Kotlin Multiplatform
Programming language	Dart	Kotlin
UI toolkit	Rich library of customizable widgets	Native UI for Android in Jetpack Compose or Views and for iOS in SwiftUI or UIKit
Code sharing	Single codebase for both iOS and Android	Shares logic implementation, platform-specific UI code
Rendering engine	Uses its own rendering engine (Impeller)	Uses native rendering
Hot Reload feature	Yes	No
Performance	High performance with a native feel, superior app startup times, smooth animations	Native-like performance due to leveraging native functionalities and APIs
Development speed	Rapid development with one UI implementation and Hot Reload	Slower development due to the need for platform-specific UI implementation
Platform-specific features	Access platform-specific code through the Platform Channels mechanism	Access platform-specific code directly without any bridges
Community support	Large, rapidly growing, substantial support on platforms like GitHub and Stack Overflow	Steadily growing support that is small but strong, due to official Google support for Android development
Use cases	Suitable for applications needing rapid development and a single codebase, ideal for MVPs	Ideal for projects requiring native performance and extensive use of platform-specific features, great for migrating highly developed projects
Adoption examples	Google Ads, Alibaba, Hamilton, myBMW, Philips Hue	Netflix, McDonald’s, Forbes, 9GAG, Bolt, Google Docs

This table highlights the key differences for choosing between Flutter and Kotlin Multiplatform based on your project needs and team capabilities.

Read also: Native vs. Cross-platform App Development – All You Need to Know as an Entrepreneur

Flutter vs. Kotlin Multiplatform – Detailed comparison

As mentioned above, Flutter and Kotlin Multiplatform are both great solutions for a cross-platform project. The choice depends on your resources, project requirements, and business goals. Let’s look at some details about each technology to help you make the right decision. 

What is Flutter?

Flutter is an open source UI development framework created by Google. It was officially launched at the Google I/O conference in December 2018. 

With Flutter, developers can create natively compiled applications for multiple platforms from a single code base. This includes iOS, Android, Windows, macOS, Linux, Google Fuchsia, web, and embedded devices.

Flutter uses the Dart programming language, known for its efficiency and performance, making it well suited for mobile application development.

Read also: Top Flutter Apps: Real-World Examples & Business Stories

Flutter advantages

Here are some of the most significant Flutter benefits. 

• Single code base: With Flutter, you write once, and run on multiple platforms (Android, iOS, web, desktop), reducing development time and effort.
• Hot Reload: Instantly see development-level code changes without restarting the application, speeding up the process.
• Rich set of widgets: Flutter offers a wide range of customizable widgets for creating visually stunning and responsive UIs.
• Performance: Dart’s ahead-of-time (AOT) compilation and Flutter’s use of native code result in high-performance apps that rival natively developed applications.
• Open-source and community-driven: There is a large and active Flutter developer community that provides continuous improvement and support, alongside numerous plug-ins and packages.
• Access native features: You can easily integrate device-specific functionality using Flutter plug-ins to access native device features and APIs.

Flutter disadvantages

Even though Flutter is one of the most popular cross-platform technologies, it’s not without its drawbacks. Here are some that you should consider while choosing the right solution for your project.

• App size: Flutter apps tend to be larger, requiring more storage and longer download times than smaller native apps. This is because you always download the Flutter engine with Flutter apps, resulting in an additional layer that adds 3-4 MB to the total weight of the app.
• Performance concerns: Although Flutter has significantly improved in performance, it might not fully match the native experience, as it uses a bridge to interact with native features.
• Limited access to native features: Flutter relies heavily on third-party plugins to access the native functionalities of mobile devices. While many plugins are available and effective, they may not support all features, particularly the more advanced and complex ones.
• Limited access to the latest system features: Native apps get immediate access to new Android and iOS features. Flutter, on the other hand, may experience delays or no access at all as it requires updates to support these features.
• Dart adoption: Dart is less widely used than other programming languages, which can create a learning curve for some developers. However, both its community and usage are growing.
• Rewriting an established native application: If you already have a well-developed and established native application, migrating to Flutter may require rewriting the entire application from scratch.

What is Kotlin Multiplatform?

To understand Kotlin Multiplatform, you first need to know about Kotlin, a modern programming language developed by JetBrains, the creators of many of the top programming tools on the market. 

Even though it’s widely associated with the Android platform, Kotlin was not designed to be an Android-specific technology. Instead, the idea behind Kotlin was to create a universal language that works well with other programming languages and can be used to build applications for multiple platforms. 

Kotlin is a multiplatform language by design. So why do you need Kotlin Multiplatform and what is it?

KMP is a set of official tools for developers that organize and simplify the process of using the Kotlin language on multiple platforms simultaneously (Android, iOS, web, desktop, and server-side applications).

In a KMP project, most of the code only needs to be implemented once in Kotlin before being easily reused in different native applications.

Thanks to this shared code, you can build full-featured native applications much faster and with less effort.

Kotlin Multiplatform advantages

Here are some of the most significant KMP benefits. 

• Superior performance: Kotlin Multiplatform (KMP) delivers native application performance that matches the efficiency and speed of applications built without KMP.
• Full access to platform-specific APIs and libraries: You can use any native technology and combine it with Kotlin Multiplatform, which is ideal for apps relying on native solutions like AR.
• Shared codebase: You can develop shared code across platforms, reducing duplication and maintenance efforts.
• Easy migration: If you have a working native application, migrating to KMP is easy. Developers can move Kotlin code to KMP iteratively, without having to rewrite the entire app, as would be necessary with Flutter. This approach allows changes to be made without changing the UI, avoiding additional costs during the migration process.
• Native UI: With KMP, you can do platform-specific UI implementations, enabling the use of the latest UI frameworks like SwiftUI and Jetpack Compose.
• Platform-specific customization: You can customize your apps’ look and behavior to follow platform design guidelines, ensuring a native look and feel.
• Full potential of Kotlin: You can use all Kotlin features, including strong typing, null safety, and coroutines, in cross-platform projects.
• Growing ecosystem: With KMP, you can benefit from an expanding ecosystem with increasing library support and community contributions.

Kotlin Multiplatform disadvantages

As with every solution, KMP also has its drawbacks. Here is what you need to know. 

• Libraries are still in the early days: In areas like architecture or testing, KMP doesn’t yet have as many programming libraries as Flutter.
• Limited online resources: There are fewer resources available for KMP compared to more established tools, though this is expected to improve as the KMP ecosystem grows.
• Early-stage UI sharing: KMP allows for joint UI development with Compose Multiplatform, but it’s still in its early stages and doesn’t yet match Flutter’s power for a fully unified codebase.
• Objective-C limitations: Translating Kotlin code to Objective-C for iOS apps can lead to certain limits and unpredictable behaviors, such as issues with default method parameters.

Flutter vs. Kotlin Multiplatform – Main differences

Now, let’s take a look at what distinguishes Flutter and Kotlin Multiplatform and why one can sometimes be a better fit than the other. 

Technical approach

Flutter and Kotlin Multiplatform are very different in their technical approach. Flutter uses Dart and compiles the code into a native binary that includes an additional Flutter engine. This engine, written in C++, runs on the device and controls every pixel on the screen, adding about 3-4 MB to the app size. This setup helps Flutter apps to run on different devices via this intermediate layer. 

KMP, on the other hand, compiles Kotlin code directly into the native code of each platform without any additional layers, enabling the system to run the code as if it were a regular native application. KMP integrates seamlessly with the native code and provides direct access to platform-specific APIs.

System integration

In KMP, common code can directly use native code specific to each platform, just like in regular native applications without KMP. In Flutter, however, common code accesses native code via Platform Channels, which serialize and deserialize data to move them between the Flutter Engine and the system. 

While Platform Channels generally perform well, high-frequency, data-intensive tasks might experience performance impacts due to this abstraction layer. Most functionalities in Flutter are handled by packages using Platform Channels. If no suitable package exists or a package doesn’t meet all requirements, developers need to implement this abstraction layer themselves.

Migration strategy

When it comes to migrating existing applications, Flutter and KMP offer different strategies. Migrating to Flutter often involves rewriting the entire application in Dart, which can be a lengthy process for large, mature applications, potentially taking months or even years. However, Flutter also allows specific features to be written in Dart and integrated into native applications, which is useful for isolated functionality.

KMP takes a more incremental approach. Instead of rewriting the code, we can gradually move it from the Android application to the Multiplatform module and then integrate in the iOS application. Migration with KMP typically starts with abstract elements such as data models, then moves to business logic, and finally to the presentation layer, while maintaining the native UI throughout. This strategy ensures a high quality user experience and familiarity, allowing for continuous value-add without disrupting business operations.

Read also: 

• Convert Your Native Project to Kotlin Multiplatform: Why, When and How
• Convert Your Native Project to Kotlin Multiplatform – Developer’s Guide

Flutter vs. Kotlin Multiplatform: 4 key criteria to help you decide

As you can see, KMP is ideal for reducing development costs and effort while maintaining native performance and experience. Its iterative migration process ensures business continuity while delivering incremental value. 

Conversely, Flutter is an excellent choice for new cross-platform projects, providing a consistent solution with a single code base, but it can be complex and time-consuming to migrate large existing native applications.

Let’s look at some other cases where either Flutter or Kotlin Multiplatform is a good fit.

Application focus

Kotlin Multiplatform is better suited for:

• Applications where the primary functionality involves hardware features such as AR fitting rooms, navigation, image processing, phone calling or video conferencing.
• Applications that need to take advantage of the latest Android and iOS features as they are released.
• Applications that require a user interface that closely follows Google’s Material Design or Apple’s Human Interface Guidelines.

Flutter is better suited for:

• Applications that focus primarily on UI/UX, with native functionality such as barcode scanning as a secondary concern.
• Applications that require a consistent user experience across Android and iOS, without strict adherence to platform-specific design guidelines.
• Applications that prioritize a unique and custom UI, potentially extending to web platforms in the future.

Organizational structure

Kotlin Multiplatform is better when:

• You already have a mobile app and an Android/iOS team, and you want to work with a technical partner.
• You want to integrate new components in your existing app or simplify development by leveraging a shared codebase.

Flutter is better when:

• You’re new to the industry and need a technical partner to build your first mobile application.
• You do not have a development team and need a partner to manage the entire development process.

Priorities and market environment

Kotlin Multiplatform is better suited for:

• Applications entering a highly competitive market where delivering a perfect, platform-native experience is critical.
• Applications that prioritize a native UI and the expected experience for platform users.

Flutter is better suited for:

• Apps that want to get to market quickly, especially for proof of concept or version 1.0, in innovative or uncharted territories.
• Applications that benefit from rapid development and features such as Hot Reload.

Read also:

• Flutter vs. Kotlin: Choose the Best Fit for Your Project  – Developers’ Guide
• Flutter vs. React Native – Which is Better for Your Project?

Developing with Flutter and Kotlin Multiplatform – Droids On Roids approach

At Droids On Roids, we leverage our deep expertise in both Flutter and Kotlin Multiplatform to tailor our approach to your unique product needs. By understanding your project’s specific requirements and goals, we combine our technical knowledge with strategic planning to deliver the optimal solution. Our goal is to ensure that your product is released quickly and efficiently, while maintaining the highest quality standards, enabling your product to thrive in a competitive market. Whether you need a robust native experience or a versatile cross-platform solution, we are committed to making your vision a reality.

Summary

Choosing between Kotlin Multiplatform and Flutter is like choosing between two powerful tools, each with its own strengths and advantages, to realize your vision of a multiplatform application. Understanding your priorities will help you make the right choice. Let’s sum up.
Kotlin Multiplatform is better suited for applications:

• whose main functionality and business purpose is some hardware feature. For example: clothes fitting rooms or furniture configurators in AR, apps for navigation, image processing, phone calling or video conferencing. 
• that want constant access to all the latest Android and iOS features
• where the UI/UX is more aligned with the platform’s guidelines.

This may be dictated, for example, by the high competition in the particular market area where the app will operate and an “every detail counts” approach. In these cases, it may be better to consider Kotlin Multiplatform than Flutter. 

Flutter, on the other hand, is better suited for applications:

• where we use native functionality only as an additional feature in the app. For example, a store app has a main purpose: product presentation and shopping process, but it may also have a barcode scanner.
• when the UI/UX needs to be consistent/identical between platforms.
• when it is to be highly custom and not necessarily following Google or Apple guidelines.

Remember, you don’t have to go one way or the other. Both tools offer different paths to success, depending on your project’s needs and future aspirations.

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