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Kotlin vs. Flutter: Choosing the Best Mobile Dev Framework

Kotlin vs. Flutter: Choosing the Best Mobile Dev Framework
May 21, 2021
min read

Flutter is Google’s user interface (UI) tooling kit for making iOS and Android applications from a single codebase. Kotlin, on the other hand, is the official programming language for Android development.

Both Kotlin and Flutter have their unique strengths and weaknesses. So, picking which one of the two is the better mobile development framework for your project can be tricky. Also, deciding which tool is better for your mobile development project may depend on the nature of the app you’re building.

In this post, we’ll compare both tools using five vectors that’ll help you decide which tool makes more sense for your mobile app project.

Both Kotlin and Flutter have their unique strengths and weaknesses.

1. Cross-Platform Support

Cross-platform apps are simply mobile applications built for Android and iOS devices from a single codebase. That means you create a single project and use a single technology or programming language to develop both the iOS and Android versions of an app.

Although Kotlin multiplatform exists, it’s not as mature as Flutter in this category.

In contrast to Kotlin, Flutter lets developers code UI elements for iOS and Android with the same code using Flutter widgets.

For example, Text() is a widget in Flutter. If you include this widget in your app just once, Flutter will take care of rendering the widget for both platforms. If you need to specify some custom styling for each platform, Flutter also has you covered with the Material and Cupertino style widgets.

In contrast, the less popular Kotlin Multiplatform Mobile lets you write UI code using separate code for iOS and Android. However, it allows you to use the Kotlin programming language for both platforms.

In short, Flutter is more popular and stable. This means more resources and a larger community to find help from when you get stuck.

Now, let’s talk about application programming interfaces.

2. Access to Device API

Both iOS and the Android operating system have APIs that let developers access core resources on the devices, including the camera, GPS, and microphone. When the latest versions of iOS and Android are released, these APIs usually get new features and improvements.

As stated earlier, Flutter lets you write UI elements for both iOS and Android from a single codebase. Flutter also behaves in a similar way when you’re trying to access device resources. However, the native APIs for iOS and Android are very different. To unify things, the Flutter software development kit does some work in the background to handle things the right way for each platform—and this brings some limitations. For example, gaining access to the latest device APIs takes longer in Flutter than it does in Kotlin.

Kotlin as a native programming language for the Android operating system has direct access to device APIs. In other words, Kotlin is better at delivering apps that use resources such as camera, GPS, and microphone.

Let’s look at another way to compare Kotlin and Flutter.

3. Speed and Performance

Users love apps that are fast, responsive, and don’t drain limited device resources, such as battery, RAM, and storage. So, speed and performance are vital.

Native Android apps built with Kotlin run faster than Flutter apps. This is mostly because Kotlin apps don’t have to run inside any container. Instead, they interact with the device directly as the operating system permits.

How do things work for Flutter apps? A platform-specific embedder provides an entry point into the app. This embedder is also responsible for coordinating access to resources. This leads to slightly slower performance in Flutter apps when compared to Kotlin. However, the difference is negligible in the case of most apps. Therefore, Flutter still delivers reliable performance.

Developing and debugging Flutter apps is fast. Thanks to hot reload and hot refresh, you can view changes made to your app during development without recompiling the entire app every time. This can save you, the developer, minutes or even hours of development time!

4. Syntax

Dart, the programming language for developing Flutter apps, has many interesting features that make life easier for developers. For example, Dart’s support for UI components called widgets removes the need for a separate XML file that handles UI design, as you’d have in native development with Kotlin. In other words, in Flutter, widgets are declared right inside the Dart code. Dart’s an object-oriented programming language and feels like Java. Therefore, if you’re already familiar with Java or JavaScript, learning Dart won’t be painful.

On the other hand, with Kotlin, you won’t need to write as much boilerplate code. A good example of this statement is the implementation of a model plain old Java object (POJO) in Kotlin. That is to say, you can create a POJO that has getters and setters with just a single line of code. Also, in Kotlin there’s no need to end each statement or line of code with a semicolon.

Both Kotlin and Dart have their unique strengths and solve the problems in their domain very well. Hence, in this category, there’s no better or worse choice.

Let’s look at one more factor.

5. Testing and Testability

The last but not the least vector is testing. It’s an essential software development process—the practice of verifying that your app or code behaves as expected.

A common form of test that you might have already performed is to deploy your app to an emulator or physical device to confirm that it works. However, that kind of test is manual. Programming languages and other software development tools offer a better way of automating tests using code. In other words, tests are generated with code. Tests can be in the form of unit tests, integration tests, or full implementation tests.

The last but not the least vector is testing. It's an essential software development process—the practice of verifying that your app or code behaves as expected.

Flutter provides some great tools that enable developers to test their apps during development. You can write unit tests for the smallest functional parts of a Flutter app using the unit testing tool. Also, you can write tests for widgets to verify that they behave as expected, and you can also do integration testing using Flutter’s test driver. What’s more, it’s possible to provide external classes and dependencies during testing using mocks.

Similarly, in Kotlin for Android development, there’s full support for Android unit tests and Android instrumentation tests.

Waldo makes a no-code testing solution for mobile that you can use to automate tests for both Flutter and Kotlin apps. There’s a lot on the Waldo site about mobile engineering and mobile design. You can try Waldo for free.

Summing Up

To conclude, let’s look at a summary of all the comparisons in this post.

Kotlin vs. Flutter chart

From the table, it’s clear that Flutter and Kotlin win in one category each and tie in three categories. Therefore, picking the better mobile development framework out of the two depends on what your priorities are and the nature of the app you’re going to build. For example, if you’re building a camera app, Kotlin will be the wise choice, as it shines in accessing the camera API. But for an e-commerce or shopping app, Flutter will enable you to reach more customers faster. That’s because Flutter lets you serve the same code to both iOS and Android users.

This post was written by Pius Aboyi. Pius is a mobile and web developer with over 4 years of experience building for the Android platform. He writes code in Java, Kotlin, and PHP. He loves writing about tech and creating how-to tutorials for developers.

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