Optimizing Flutter App Performance

Best Practices, Widget Building Tips, and Architectural Impact

6 min readSep 13, 2023

As a software developer, more than delivering a solution to a problem through software, it is also necessary to pay attention to the user experience. The challenge lies in selecting the right technologies and devising clever solutions that utilize resources efficiently without compromising user experience. This principle holds true across all technologies, including Flutter. While the Flutter framework itself is designed to empower developers to build high-performance applications, the responsibility still falls on developers to harness its potential.

With that in mind, we will in this article delve into the crucial aspects that determine the performance of Flutter applications, exploring best practices, widget-building tips, and the profound impact of architecture.

App Performance

First things first, what does it take for an application to be well performant? What are the criteria?

A mobile application specifically differs a little bit from a web application, especially in how the end user interacts with it, and how/what they expect while using them. For instance, when the user interacts with an element in a web application, he understands that the expected action depends on the browser making a call to the server — well, maybe the end user will call it just “the internet” — but in a mobile application, the expectation is for an immediate response of the tap action, at the risk of the user tapping the button once again after one second or even less time of delay, and after 3–4 seconds user might want to leave the app or restart the application.

A well-performant mobile application will be measured by how responsive it is, how quickly it starts up, how well it uses device memory, how well it uses device power, and in the case of animations or games how high its frame rate or how smooth the animation or game is. With that in mind, we can have some key factors to be used as benchmarks such are: the application's overall design (how it communicates with the user), memory and power usage, network handling, and overall architecture of the application.

Memory management

Flutter (the engine) uses a garbage collector approach to manage memory, which will constantly be checking for unused memory and claim, meaning it will map out widgets that are in use and those that aren’t and then release memory if a widget is no longer using it. But with that in mind, it’s important to be mindful of memory usage and improper disposal of objects, or failure to close listeners that are no longer needed, dispose of resources properly, especially in instances, to prevent memory leaks which can happen due to caching, large image, and video loading without releasing them properly which can be addressed using the isolates approach or reducing the size of the files if justifiable. It is also important to note stream subscriptions, failing to cancel them, will keep running in the background and consume memory unnecessarily. Other than efficiently dealing with large resources loading, canceling subscriptions, and disposing of objects in stateful widgets manually, some resources can be used to help achieve better memory management:flutter_cache_manager, leak_detector, flutter analyze, paying attention profiling tools such as the Flutter DevTools and command to detect memory leaks efficiently, redundant objects and other memory-related issues.

Lazy Loading

Lazy loading is a technique for loading resources only when they are needed. This can improve performance by reducing the amount of data that needs to be loaded at once. One example of this is the infinite scroll implemented across almost all social media apps. This approach in Flutter can be addressed by simply using options like cached_network_image, which enables you to efficiently manage remote images, ensuring they are only fetched when they are needed, and more packages that can be found depending on your specific use case, and with the use of widgets like ListviewBuilder (which we’ll address later in the article).

Widget Usage

Widgets are the most important part of a Flutter app, and Flutter uses a reactive approach to UI, which means that widgets rebuild themselves when their state changes. However, excessive widget rebuilding can lead to unnecessary performance overhead, and we can avoid that by using the const keyword for widgets that don’t change and employing the Stateful widgets and Stateless widgets efficiently by segregating mutable and immutable parts. It is also important to opt to use simpler widgets like SizedBox and Text over complex ones. Also, leverage widgets with built-in caching mechanisms such as Listview.builder to efficiently handle lists of dynamic content.

Animation Optimization

Animations make communication with the end user more fun and interactive, and although they add life to the app, if used improperly can lead to a janky experience, it’s important to handle it carefully. For better management and experience, we can use AnimationController and Rive. AnimationController acts as a time-based controller for animations, allowing us to precisely control animation duration, easing curves, and intervals instead of perhaps just starting abruptly when triggered, resulting in the animation feeling fluid and natural. Most importantly, eliminates the risk of jarring jumps or pauses in animations, contributing to a more polished user experience. Rive enables developers to create and integrate complex animations seamlessly and represents those animations as lightweight vector graphics, which means that even intricate animations can be stored and rendered efficiently, ideal for scenarios where complex animations are needed.

Widget Building Tips

Avoid using nested widgets: nested widgets can make the app less performant, instead, opt to create individual classes for widgets and clearly segregate Stateful and Stateless widgets.
Use keys: Keys help Flutter identify widgets across updates, minimizing the need for complex builds.
Context Usage: Avoid passing BuildContext when it’s not needed as it can trigger unnecessary widget rebuilds, leading to inefficiency. Make sure to use it in a more conscient way, that way ensuring app performance is consistent.
Use the right kind of widget for the job: Some widgets are more performant than others. For example, Row and Column are more performant than Stack. Make sure you are making a conscious decision about which widget is being used according to the need.

The Architectural Impact on App Performance

An often-underestimated aspect of Flutter app performance is the architecture. A well-designed architecture can significantly influence how efficiently an app runs:

State Management: The chosen state management approach plays a vital role. Options like Provider, Riverpod, and BLoC offer different ways to manage app state, affecting reactivity and resource usage.
Separation of Concerns: The different parts of your app should be separated into different layers, each with its own responsibility. This will make it easier to understand and maintain your code, and it will also make it easier to optimize performance. Implementing a clean architecture, such as the BLoC (Business Logic Component) pattern, can aid in isolating UI, business logic, and data layers. This separation enhances code maintainability and performance.
Code Splitting and Modularization: Breaking down your app into smaller, modular components allows for efficient code splitting. This means that only the necessary parts of the app are loaded when required, reducing initial loading times.
Reusability: Code that is used in multiple places should be made reusable. This will reduce the amount of code that you need to write, and it will also make it easier to optimize performance.
Data locality: Data that is frequently used should be kept close to the code that uses it. This will reduce the amount of data that needs to be transferred between different parts of your app, and it will also make it easier to optimize performance.

Conclusion

As software developers, crafting high-performance applications is both an art and a science. While Flutter equips developers with a powerful framework, it’s the developer’s responsibility to wield it optimally. By opting to use best practices, employing smart widget-building techniques, and adopting a well-considered architectural approach, Flutter apps can attain the performance levels users expect. Remember, the framework is the tool, but the engineering choices make all the difference. So, go forth and build performant, delightful Flutter applications that leave a lasting impression on users.

I tried to cover more than what is explained in the Flutter Documentation, so, if you haven’t read it yet consider checking it here. It’s a great resource to really grasp performance concepts. Also, I listed below resources that I used to write this article and others that I simply use as reference guides to keep learning how to improve app performance.

Useful Resources (not just related to Flutter specifically):

Thank you for reading. I hope you enjoyed it and learned from it.

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For questions and/or suggestions, I am available through the comments section, email igorlsambo1999@gmail.com or 𝕏 @lsambo02.

Thank you and we will catch up on the next article!!!