Flutter vs. Kotlin: Choose the Best Fit for Your Project  – Developers’ Guide

In today’s world, mobile app development is rapidly evolving. Developers are constantly looking for efficient and versatile frameworks – something that can help them build high-quality applications with ease. Two popular choices for the Android platform are Flutter and native Android.

Flutter, developed by Google, is an open-source UI toolkit. It allows us to create beautiful and fast applications. It uses the Dart programming language and supports both mobile, web, and desktop platforms using a single codebase.

On the other hand, modern native Android apps use Kotlin as a main programming language. But, there is a full interoperation with Java and the JVM ecosystem. 

In this article, I will explore the differences and similarities between those approaches. That should help you make a decision about which framework to choose for your next app project. 

At Droids On Roids, we excel in crafting high-quality digital products through both native and cross-platform methods, customizing solutions to align with specific project requirements and our clients’ goals. As a mobile developer with hands-on expertise in both Kotlin and Flutter, I’m eager to share my insights with you.

So, let’s dive in!

Flutter vs Kotlin: Programming languages differences

Kotlin and Dart are two popular programming languages for mobile app development (the latter being a programming language used by Flutter). Both are capable of building robust and feature-rich applications. However, there are some key differences that developers should be aware of.

Kotlin

Kotlin is a statically-typed language that runs on the Java Virtual Machine (JVM). It’s a natural choice for Android app development, offering seamless interoperability with Java. This enables developers to leverage existing Java libraries and frameworks. Kotlin is also used for server side programming. There are many backend frameworks written in Kotlin, too.

Dart

Dart is a dynamically-typed language. It is primarily used with the Flutter framework. Its Just-In-Time (JIT) compilation allows for hot-reloading. That makes the app development process much faster and more efficient. There are several server-side Dart frameworks but the language’s popularity on the backend side is very low. It is possible to develop the production-ready backend services in Dart. However, there are much more resources, tools and teams available in the popular technologies like Node.JS, Python or Go.

Kotlin vs Dart: The ecosystems

In terms of community support and ecosystem, Kotlin has a strong advantage. It has been embraced by the Android community and has a large and active developer community. There are many resources, libraries, and frameworks available for Kotlin. So, it is easier for developers to find help and build robust applications. 

Dart, although growing, has a smaller community compared to Kotlin. According to the statistics gathered by libraries.io there are about 50k packages on Dart’s pub.dev and 588k on Maven central at the time of writing. 

Those two repositories are not the only ones available for each platform, especially in the case of the Java ecosystem. Nevertheless, a tenfold gap is a huge difference. Yet, with the rise of Flutter’s popularity, the Dart ecosystem is also expanding. More resources and libraries are becoming available.

Kotlin has plenty of well-known libraries for common tasks like DI or HTTPS requests. Many of them are maintained by companies like JetBrains or Square. In contrast, many of the popular Flutter/Dart packages are powered by various communities. They rely on individual contributors working in their free time. The support in such cases may not be so stable. 

For example, the most popular HTTPS client – dio, had no active maintainer for several months at the end of 2022. See this Reddit thread for more details. Finally, the new maintainer was found in early 2023 (see this issue for more details). However, it was not a good sign for thousands of projects using that library.

Dart vs Kotlin: The language features

Both languages offer modern features. For instance: null-safety, sealed classes or smart casting (non-null promotion in Dart). Yet most of them land earlier in Kotlin. For example Kotlin has been null-safe since the beginning. In Dart, it was added in version 2.12.0 in 2021. 

When it comes to smart casting, Kotlin provides more advanced smart casting capabilities compared to Dart. Kotlin’s smart casting allows for automatic type casting when certain conditions are met. For example, if an object is checked for a certain type within an if statement, Kotlin automatically casts it to that type within the if block. This eliminates the need for explicit type casting. 

Dart, on the other hand, does not have the same level of smart casting as Kotlin. In Dart, explicit type casting is required when switching between different types.

It takes some time to adapt to the new core language features. Even if you have the capacity to modify the code of your app immediately, you have to wait until the library maintainers do that.

The Flutter build system is not as versatile and easy to use as its native brother. For instance, there is no such tool like Gradle in Flutter. Of course, you can, for instance, use the build_runner package for code generation. But, there is no way to automatically invoke it using only the utilities from the Flutter SDK. You have to rely on shell scripts, CI workflows and/or instructions in Readme files.

Dart vs Kotlin: Adopting to system updates

There are differences between native development and Flutter in adopting changes introduced in new Android or iOS versions. Native development typically allows for faster adoption of platform-specific changes. This is because developers working on native Android or iOS apps have direct access to the latest APIs, tools, and documentation provided by Google or Apple. They can leverage these resources to quickly update their apps and take advantage of new features or optimizations introduced in the latest platform versions.

On the other hand, Flutter’s adoption of changes introduced in new Android or iOS versions may take slightly longer. Flutter acts as a layer of abstraction between the app and the platform. It relies on updates and improvements made by the Flutter framework itself to incorporate new platform features. 

Flutter developers often need to wait for the Flutter team to release updates that support the latest platform changes. However, the Flutter team is dedicated to ensuring timely updates and compatibility with new platform versions. And they actively work on incorporating platform-specific features into Flutter’s framework. Adapting all the dependencies (packages, libraries) will take additional time. All that can result in a slight delay in adopting platform-specific changes.

Flutter vs Kotlin: Differences in the app development process

At the planning level, the app development process differs in terms of resource allocation and team structure. In native Android development, one or more developers works only on the app for their platform. Another set of developers may be assigned separately to work on the iOS platform using Swift and the iOS SDK.

Flutter app development, in contrast, follows a cross-platform approach. A single team of developers can handle both the Android and iOS platforms using the same codebase. This is because Flutter uses a single language, Dart, and a single set of widgets for building user interfaces. With Flutter, developers can write code once and deploy it to multiple platforms.

See: Top Flutter Apps: Real-World Examples & Business Stories

You may think that Flutter is great due to reducing the need for separate platform-specific teams. The lesser number of involved developers the lesser costs. Indeed, it may be true. But, it’s not correct in all the cases. 

If the app codebase can be pure (or almost pure) Dart, then of course it is more efficient to use Flutter. However, the more platform-specific code, the better native development may be. Keep in mind that most Flutter developers have the majority off their experience in Flutter. Some of them may have backgrounds in one of the native platforms, but not both. There are very few people holding a senior level in both Android and iOS. A person with lower experience in a given technology may need more time to develop a certain feature in another technology. What is more, the quality of their code may be lower when compared with code from a native developer.

The complexities of separate iOS and Android teams

On the contrary, if there are two separate development teams, the products they are creating may differ from each other. I’m not talking about visual distinctions or platform-specific behaviors. For example, there might be different interpretations of the requirements. Even if the entire team has common meetings like refinements. It may be impossible to align all the details. 

In some cases, the consistency between platforms is more important than the final effect. For instance, the designs may be for iOS only or just the iOS version was presented sooner and stakeholders want that solution instead of something following Android guidelines. As you can see, such discrepancies may be discovered after the development, such as during the QA or UAT phase. They may introduce additional work for one of the platforms, usually for the team that finished a given feature later. This increases the difference in development time even more. And here we come to another stage.

Native iOS development is often considered faster than Android development. iOS has a more controlled hardware ecosystem with a limited number of device models and configurations. This allows developers to optimize their apps specifically for these devices. It further results in better performance and fewer compatibility issues. 

In contrast, Android has a vast array of device manufacturers. Each of them use their own hardware specifications and customizations. This fragmentation can introduce complexities and challenges during the development and testing process.

In most real-world apps, iOS development is faster than Android. That discrepancy may cause many issues. For example, it can lead to friction between team members. Moreover, the customer may not understand or even be interested in the differences between platforms. That may create additional pressure on the “slower” team.

Yet another source of differences between platforms is engagement. For example, the developers of one platform may write a lot of tests, such as unit, UI, integration, or even mutation tests. If, on the second platform, the number of tests is significantly lesser then it may take them less time to deliver the same feature. What is more, developers of one of the platforms may decide to handle or distinguish more edge cases.

In the case of Flutter apps, there is usually one codebase and one development team. Even if there are differences in the engagement and/or seniority of the individual developers, they are not visible outside. They ship features equally for both of the platforms by default. There are no differences between platforms caused by the aforementioned reasons. That is a key advantage of Flutter.

In summary, when there are separate iOS and Android development teams, the products they create may differ from each other, not just in terms of visual distinctions or platform-specific behaviors, but also in their interpretation of requirements. In contrast, Flutter apps have a single codebase and development team, eliminating platform differences caused by separate teams. This is a benefit of Flutter in those terms.

Flutter apps can usually be developed faster and cheaper than native ones. Using Flutter can also reduce differences between platforms. However, if the app needs a significant amount of native code (because the given functionalities are not available in Flutter) then choosing a native app will often be a better choice. Flutter may also be a good option for MVP (Minimum Viable Product), MMP (Minimum Marketable Product) or PoC (Proof of Concept) project stages.

Advantages of Kotlin and Flutter

Advantages of Kotlin

• Native performance: Kotlin for Android and Swift for iOS offer native performance, as they are specifically designed for their respective platforms. This can result in faster and more efficient apps compared to Flutter’s cross-platform approach.
• Platform-specific APIs: Kotlin and Swift provide direct access to platform-specific APIs, allowing developers to leverage the full capabilities of the underlying operating systems.
• Mature ecosystem: Kotlin and Swift have been around for a longer time and have well-established ecosystems. This means there is a vast range of libraries, tools, and resources available to aid in development, making it easier for developers to find solutions and address challenges.

Advantages of Flutter

• Cross-Platform development: Flutter enables cross-platform development, meaning that a single codebase can be used to create apps for both iOS and Android platforms. This saves time and effort, since developers don’t have to write separate code for each platform.
• Hot Reload: Flutter offers a hot reload functionality, allowing for real-time code updates and faster iteration during the development process.
  Read more: Pros and Cons of Flutter App Development

Next, I’d like to delve into an interesting solution that Kotlin provides for cross-platform development and compare it with Flutter. 

See a brief summary in the form of a graphic:

Kotlin Multiplatform vs Flutter

What is Kotlin Multiplatform?

Kotlin Multiplatform is a cross-platform technology that enables developers to share code between different platforms, primarily for Android, iOS, and web applications. It is an extension of the Kotlin programming language. It enables the creation of common modules containing business logic, data models, and utility functions that can be shared across platforms. With KMP, developers can write platform-specific code for UI and platform-specific features.

	Flutter	Kotlin Multiplatform
Programming language	Dart	Kotlin
Created by	Google	JetBrains
Community support	Large community (51k repositories on GitHub)	Growing community (1,5k repositories on GitHub)
Performance	High performance with a custom rendering engine	Native performance on Android, but slightly worse on other platforms
UI Consistency	Consistent UI across all platforms or adaptive UI	Native, platform-specific UI
Learning Curve	Easier for beginners with extensive documentation	Steeper, but more familiar to Android developers
Codebase	Single codebase for multiple platforms (iOS, Android, web, Windows, macOS, Linux)	Shared business logic with platform-specific UI code (iOS, Android, desktop, web)

Key pros of Kotlin Multiplatform

Kotlin Multiplatform’s key advantages lie in its ability to fuse the benefits of shared business logic. The primary pro is the significant reduction in code duplication, as developers can write the core logic once and use it across many platforms. KMP allows for the leveraging of Kotlin’s expressive and concise language features, enhancing code readability and reducing the potential for bugs. 

Moreover, it provides full access to each platform’s native APIs, enabling developers to create fully native user experiences without compromises. Lastly, KMP promotes a collaborative environment between iOS and Android teams, fostering communication and code sharing.

Key cons of Kotlin Multiplatform

Despite the advantages of Kotlin Multiplatform, there are several cons to consider as well. One of the main drawbacks is the relative immaturity of the ecosystem compared to established platforms like Android and iOS native development. Another challenge is the learning curve associated with understanding the KMP architecture and the best practices for sharing code between platforms, which can be steep for teams new to the concept. Finally, while KMP is strong in sharing business logic, it still requires platform-specific UI code,  potentially limiting the efficiency gains in the UI layer of development.

To sum up, when your goal is to create cross-platform mobile apps using just one codebase and a fully native UI isn’t a top priority, Flutter could be the more suitable option because of its rich ecosystem and straightforward development process. Conversely, if your focus is mainly on Android and iOS and you aim to share business logic across these platforms while leveraging native UI elements, Kotlin Multiplatform Mobile (KMM) might be the right choice, particularly if you have experience with Kotlin.

Read also: 4 Most Popular Cross-Platform App Development Frameworks for 2023

Flutter vs Kotlin trends

The trends between Flutter and Kotlin reflect a broader movement in the industry. Developers are increasingly looking for tools that offer both productivity and performance. Flutter appeals to developers who want to target multiple platforms with a single codebase. Kotlin is preferred by those who are developing exclusively for Android but want a more modern and expressive language than Java. 

However, according to the recent Google Trends, Kotlin Multiplatform is an emerging trend. This could potentially shift some of the momentum back towards Kotlin if it gains traction and proves to be a robust alternative for cross-platform development.

Kotlin or Flutter – what do we choose at Droids On Roids?

At Droids On Roids, we create software products using both Flutter and native development for each platform chosen by our clients. When it comes to Android, Kotlin is our go-to language.

Each client project is unique. We carefully analyze the specific needs and requirements to determine the best fit. Recently, Flutter has been our frequent choice for its versatility. However, we go with the native development in case of the maintenance of apps with existing native codebases. Contact us if you’re looking for experienced app development team.

Kotlin vs Flutter: Wrap-up

Ultimately, the decision between Flutter and native iOS/Android development should consider several factors. This includes project requirements, available resources, development timeline, and the specific needs of the target audience. Both approaches have their own strengths and considerations, so it’s important to evaluate them in the context of your project to make an informed decision.

	Flutter	Kotlin
Language used	Dart	Kotlin
Origin/ owner	Google	JetBrains
Development environment	Android Studio, VS Code	Android Studio, IntelliJ IDEA
Cross-platform capabilities	Android, iOS, web, Windows, Linux, macOS, Fuchsia	Stable: Android, iOS, Desktop (using JVM), server-side (using JVM), web (using JS)Alpha: web (using Wasm)Best-effort: tvOS, watchOS
Cost-effectiveness	Very effective	Quite effective
Community support & Compatibility	Wide community support, moderate compatibility	Moderate community support, high compatibility
Hot-reload	Yes	No
Backend support	Yes	Yes
Integration of Third-Party Libraries	Limited	Wide
UI Experience	Custom or native-like	Native
Documentation & learning resources	Very high availability	High availability
Backward compatibility	Low	High
Testing & debugging tools	Some tools	Rich set of tools

When deciding whether to choose Flutter or native development with Kotlin, it’s essential to consider your project’s specific requirements. Flutter offers a rapid development cycle, a single codebase for multiple platforms, and a rich set of pre-designed widgets, making it ideal for cross-platform applications with a consistent UI. On the other hand, native Kotlin development should be your go-to for applications that demand deep integration with the Android platform, require maximum performance, or need to leverage the full spectrum of Android-specific APIs and features.

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