Optimizing Flutter Apps for Performance

November 22, 2024November 22, 2024 Divyanshu Singh Performance and Optimization

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Introduction

Understanding Flutter Performance

Factors affecting Flutter app performance

Measuring performance

Profiling performance

Why do we need to Optimize our application?

How can we optimize our flutter application?

Conclusion

References

Introduction

Optimizing Flutter apps is crucial for delivering smooth and responsive user experiences, especially on resource-limited mobile devices. As Flutter apps grow in complexity, factors like widget rebuilds, inefficient data handling, and heavy asset usage can slow performance. By focusing on efficient widget management, memory optimization, and streamlined network requests, you can significantly enhance app responsiveness and reduce memory usage. Let’s dive into some best practices and techniques to help optimize your Flutter app for peak performance.

Understanding Flutter Performance

In the context of Flutter apps, performance primarily revolves around two key metrics:

Rendering speed: This refers to how quickly Flutter can generate the pixels that make up your app’s UI on the screen. Ideally, Flutter should be able to render each frame in roughly 16 milliseconds (ms) to achieve a smooth 60 frames per second (FPS) experience. This ensures a seamless and responsive interaction for the user.
Frame rate (FPS): FPS refers to the number of times per second that the app’s UI is updated and redrawn on the screen. A higher FPS translates to a smoother and more fluid user experience. Conversely, a low FPS can lead to choppiness, lag, and a feeling of sluggishness.

Factors affecting Flutter app performance

Several factors can influence the performance of your Flutter app. Here’s a breakdown of some key contributors:

Widget tree complexity: Flutter builds your app’s UI using a hierarchy of widgets. A complex widget tree with many nested widgets can take longer to render, impacting performance.
Widget rebuild frequency: Flutter rebuilds the entire widget subtree whenever a change occurs in its state, even if the change only affects a small portion of the UI. This can be a performance bottleneck for frequently updated widgets or those deeply nested within the widget tree.
State management strategy: The way you manage your app’s state can significantly impact performance. Poor state management practices can trigger unnecessary widget rebuilds, leading to slowdowns.
UI complexity: Visually complex UIs with rich animations, heavy layouts, or large images can require more processing power to render, potentially affecting performance.
Device capabilities: The performance of your app will also be influenced by the user’s device. Devices with lower processing power, limited memory, or slower network connections will experience slower app performance.

While understanding the theoretical aspects of performance is valuable, it’s crucial to have practical tools at your disposal to measure and profile your Flutter app’s actual performance. Here’s how you can get started:

Measuring performance

Several built-in tools and techniques can help you assess your Flutter app’s performance:

Flutter DevTools: This suite of developer tools provides a wealth of information about your app’s performance. Within DevTools, the Performance view allows you to:
Analyze frame rate: Monitor the app’s FPS in real-time and identify any drops that might indicate performance issues.
Track build times: See how long it takes for widgets to rebuild during the build phase. This helps pinpoint potential bottlenecks related to complex widget trees or inefficient build methods.
Visualize the rendering pipeline: Gain insights into the different stages of the rendering pipeline and identify any bottlenecks that might be slowing down the process.
The Timeline Class: The Timeline methods add synchronous events to the timeline. When generating a timeline in Chrome’s tracing format, using Timeline generates “Complete” events. Timeline’s startSync and finishSync can be used explicitly, or implicitly by wrapping a closure in timeSync.

Timeline.startSync("Doing Something");
doSomething();
Timeline.finishSync();

Profiling performance

Profiling goes beyond just measuring performance metrics. It involves analyzing how your app utilizes resources like CPU, memory, and network bandwidth. This deeper analysis helps you pinpoint the root cause of performance issues.

Dart observatory: This tool provides detailed insights into your app’s memory usage and allocation. You can use it to identify potential memory leaks or excessive memory consumption that might be impacting performance.
Performance overlay: Flutter DevTools offer a Performance Overlay that can be displayed on top of your running app. This overlay provides real-time information about widget rebuilds, frame rate, and build times, allowing you to visualize performance issues directly within the app itself.

WidgetsApp(
  showPerformanceOverlay: true,
  // Other properties
);

Why do we need to Optimize our application?

In essence, optimization ensures the app provides a quality experience across devices, respects user resources, and stays competitive in an ever-growing market. Here are some top notch reasons for it:

1. Enhanced User Experience

Performance: Users expect smooth interactions and minimal load times. Optimization reduces lag, stuttering, and crashes, leading to a seamless user experience.
Responsiveness: Optimized apps respond faster to user inputs, making interactions feel natural and responsive, which is critical for user retention.

2. Efficient Resource Usage

Battery Life: Optimized apps consume less CPU, GPU, and memory, which can reduce battery drain — a big plus for mobile users.
Memory Management: By reducing memory usage and preventing memory leaks, you can avoid crashes and freezes on lower-end devices or when dealing with large data sets.

3. Reduced Data Usage

Efficient Network Calls: Optimization of network requests, including data compression and caching, minimizes data usage, making the app more friendly to users with limited or costly internet access.

4. Improved Device Compatibility

Support for Lower-End Devices: Optimized apps can run smoothly on a wider range of devices, including those with lower processing power and limited resources, expanding the app’s reach.

5. Higher App Store Ratings

User Satisfaction: Faster, smoother apps tend to receive better reviews. Higher ratings and positive feedback in app stores improve visibility and credibility, driving more downloads.

How can we optimize our flutter application?

There are variety of ways following which the app can be optimized.

Some of them are :

1. Optimize Widgets

Use const Widgets: Marking widgets as const helps Flutter avoid rebuilding them unnecessarily, as it knows the widget won’t change. Use const constructors on widgets as much as possible, since they allow Flutter to short-circuit most of the rebuild work. To be automatically reminded to use const when possible, enable the recommended lints from the flutter_lints package. For more information, check out the flutter_lints migration guide.

// Better: Declared as const so it won't rebuild
const Text("Hello");
// Avoid this if it doesn't change
Text("Hello");

Break Down Large Widgets: Avoid overly large single widgets with a large build() function. Split complex widgets into smaller widgets to reduce the amount of code Flutter has to re-render and improve readability.


Widget build(BuildContext context) {
  return Column(
    children: [
      ProfileHeader(), // Small widget for header
      ProfileDetails(), // Small widget for details
    ],
  );
}

Avoid Unnecessary Rebuilds: Wrap widgets in setState only when necessary to avoid excessive re-rendering of unrelated parts of the widget tree. When setState() is called on a State object, all descendent widgets rebuild. Therefore, localize the setState() call to the part of the subtree whose UI actually needs to change. Avoid calling setState() high up in the tree if the change is contained to a small part of the tree.
Use RepaintBoundary to isolate parts of the widget tree: The RepaintBoundary widget helps in isolating parts of the widget tree, preventing unnecessary repaints. This approach can significantly reduce the workload on the rendering engine.

RepaintBoundary(
  child: MyExpensiveWidget(),
);

2. Optimize complex layouts

Explore using SingleChildScrollView or GridView for layouts with long lists or grids, as they are optimized for performance.
Use ListView.builder: Using ListView.builder instead of ListView avoids rendering all items at once by creating them only when they’re visible.

ListView.builder(
  itemCount: 1000,
  itemBuilder: (context, index) {
    return ListTile(title: Text('Item $index'));
  },
);

Use GridView.builder: Using GridView.builder instead of GridViewavoids rendering all items at once by creating them only when they’re visible.
Implement lazy loading and pagination: Implement lazy loading and pagination to load data as needed, reducing initial load times and memory usage.

class PaginatedList extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      itemCount: items.length,
      itemBuilder: (context, index) {
        if (index == items.length - 1) {
          // Trigger pagination
        }
        return ListTile(
          title: Text(items[index]),
        );
      },
    );
  }
}

Use Keys for List Items: Assigning unique keys to items in a list helps Flutter efficiently track and update only the changed items.

ListView(
  children: [
    ListTile(key: ValueKey('item1'), title: Text('Item 1')),
    ListTile(key: ValueKey('item2'), title: Text('Item 2')),
  ],
);

3. Image Optimization

Compress Images: Before adding images to your assets, use compressed formats like JPEG or WebP, which are optimized for mobile.
Optimize image sizes and formats: Ensure images are optimized for size and format to reduce load times and improve performance.
Use cached_network_image for Image Caching: Use this package to store images locally, reducing the need for repeated network calls.

CachedNetworkImage(
  imageUrl: 'https://example.com/image.png',
  placeholder: (context, url) => CircularProgressIndicator(),
  errorWidget: (context, url, error) => Icon(Icons.error),
);

Consider SVGs for Simple Graphics: For icons and vector graphics, SVGs use less memory and load faster.

SvgPicture.asset("assets/icon.svg");

4. Memory Management

Dispose of Resources: Always dispose of controllers and streams in the dispose method to free up memory when the widget is removed.

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  final TextEditingController _controller = TextEditingController();

  @override
  void dispose() {
    _controller.dispose(); // Dispose of the controller
    super.dispose();
  }
}

Avoid Excessive Nesting: Excessively deep widget trees use more memory and make the code harder to maintain. Consider using functions or smaller widgets to simplify the structure.

5. Efficient Networking

Use Pagination: Only load a limited number of items at once, and load more as the user scrolls to the end of the list.


ListView.builder(
  controller: _scrollController,
  itemCount: items.length,
  itemBuilder: (context, index) {
    if (index == items.length - 1) {
      _loadMoreData(); 
    }
    return ListTile(title: Text(items[index]));
  },
);

Data Caching and Compression: Use the dio package with GZIP compression to reduce data transfer.

Dio dio = Dio();
dio.options.headers['Content-Encoding'] = 'gzip';

6. Async Operations

Use compute() for Heavy Computations: Offload tasks to a separate isolate to keep the UI responsive.

Future<int> _calculateSum() async {
  return await compute(expensiveCalculation, 1000);
}

Debounce User Input: Limit rapid user input by implementing a debounce to reduce the number of API calls or heavy tasks.

Timer? _debounce;
void onSearchChanged(String query) {
  if (_debounce?.isActive ?? false) _debounce!.cancel();
  _debounce = Timer(const Duration(milliseconds: 500), () {
    // Call your API or update state here
  });
}

7. Reduce App Size

Minimize Dependencies: Check pubspec.yaml to remove unused packages that add unnecessary weight to your app.
Enable Tree Shaking: Flutter’s tree-shaking feature automatically removes unused code in the release build.
Remove unused resources and code: Regularly audit your project to identify and remove any unused images, code, or assets that are bloating your app size. Tools like flutter analyze can help with this process.
Split APKs by Architecture: Use the --split-per-abi flag to generate APKs optimized for specific architectures, reducing the APK size.

flutter build apk --split-per-abi

8. Performance Profiling

Flutter DevTools: Use DevTools to monitor widget rebuilds, track memory usage, and diagnose CPU performance issues.

flutter pub global activate devtools
flutter pub global run devtools

In DevTools, you can visualize your widget rebuilds, analyze memory usage, and identify potential performance bottlenecks.

9. Minimize expensive operations

Some operations are more expensive than others, meaning that they consume more resources. Obviously, you want to only use these operations when necessary. How you design and implement your app’s UI can have a big impact on how efficiently it runs.

10. Control build() cost

Here are some things to keep in mind when designing your UI:

The traversal to rebuild all descendents stops when the same instance of the child widget as the previous frame is re-encountered. This technique is heavily used inside the framework for optimizing animations where the animation doesn’t affect the child subtree. See the TransitionBuilder pattern and the source code for SlideTransition, which uses this principle to avoid rebuilding its descendents when animating. (“Same instance” is evaluated using operator ==, but see the pitfalls section at the end of this page for advice on when to avoid overriding operator ==.)
To create reusable pieces of UIs, prefer using a StatelessWidget rather than a function.

11. Use saveLayer() thoughtfully

Some Flutter code uses saveLayer(), an expensive operation, to implement various visual effects in the UI. Even if your code doesn’t explicitly call saveLayer(), other widgets or packages that you use might call it behind the scenes. Perhaps your app is calling saveLayer() more than necessary; excessive calls to saveLayer() can cause jank.

12. Minimize use of opacity and clipping

Opacity is another expensive operation, as is clipping. Here are some tips you might find to be useful:

Use the Opacity widget only when necessary. See the Transparent image section in the Opacity API page for an example of applying opacity directly to an image, which is faster than using the Opacity widget.
Instead of wrapping simple shapes or text in an Opacity widget, it’s usually faster to just draw them with a semitransparent color. (Though this only works if there are no overlapping bits in the to-be-drawn shape.)
To implement fading in an image, consider using the FadeInImage widget, which applies a gradual opacity using the GPU’s fragment shader. For more information, check out the Opacity docs.
Clipping doesn’t call saveLayer() (unless explicitly requested with Clip.antiAliasWithSaveLayer), so these operations aren’t as expensive as Opacity, but clipping is still costly, so use with caution. By default, clipping is disabled (Clip.none), so you must explicitly enable it when needed.
To create a rectangle with rounded corners, instead of applying a clipping rectangle, consider using the borderRadius property offered by many of the widget classes.

13. Leverage asynchronous programming

Asynchronous programming is essential for maintaining a responsive UI.

Use async/await effectively: Using async and await allows your app to perform non-blocking operations, keeping the UI responsive.

Future<void> fetchData() async {
  final data = await apiService.getData();
  // Process data
}

Avoid blocking the main thread: Ensure that heavy computations and long-running tasks are performed off the main thread to prevent UI freezes.

compute(expensiveFunction, data);

14. Optimize network calls

Efficient network handling is crucial for app performance.

Use efficient APIs and data formats: Optimize your APIs and use efficient data formats like JSON to reduce payload sizes and improve response times.
Implement caching strategies: Implementing caching mechanisms can reduce the number of network requests and improve performance.

class CacheService {
  final _cache = <String, dynamic>{};

void cacheData(String key, dynamic data) {
    _cache[key] = data;
  }

dynamic getData(String key) {
    return _cache[key];
  }
}

Reduce the number of network requests: Batching requests and minimizing unnecessary network calls can significantly enhance performance.

Conclusion

By following these best practices and exploring advanced techniques, you can significantly improve the performance of your Flutter app. Ultimately, these optimizations not only enhance app performance but also broaden device compatibility, improve user retention, and lead to higher app store ratings. With these strategies, your Flutter app can achieve both technical excellence and user satisfaction. Remember, performance optimization is an ongoing process. As your app evolves, revisit these strategies and adapt them to your specific needs.

At What the Flutter, we love working with Flutter apps to make them high-performing that delight users. Contact us today to discuss how we can optimize your Flutter app performance.

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References:

Performance best practices
How to ensure that your Flutter app is performant.docs.flutter.dev

How to Improve Flutter App Performance: Best Practices
Discover the best practices and optimization techniques to enhance your Flutter app performance for smooth and…blog.flutter.wtf

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