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Common Bugs and Performance Issues in Flutter Apps


Common Bugs and Performance Issues in Flutter Apps

Flutter has gained immense popularity among mobile app developers due to its ability to create high-performance and visually appealing cross-platform apps. However, like any other technology, it has its fair share of bugs and issues that can impact the performance of the app.


In this blog, we will discuss some of the most common bugs and performance issues that developers face while developing Flutter apps.


State Management Issues


One of the most common issues that developers face in Flutter is state management. If not handled properly, state management can lead to bugs and performance issues. When the app's state changes, it can lead to a chain of rebuilds in the widgets tree. This can affect the app's performance and lead to lag and jank.


To handle state management in Flutter, developers can use stateful widgets or state management libraries like Provider, Redux, MobX, or BLoC. These libraries help to manage the app's state efficiently and minimize rebuilds in the widget tree.


Memory Leaks


Memory leaks occur when objects that are no longer needed are not disposed of properly, leading to excessive memory usage. In Flutter, memory leaks can occur when widgets and their associated objects are not disposed of when they are no longer needed.


To avoid memory leaks, developers can use the dispose() method to dispose of objects when they are no longer needed. Developers can also use Flutter's built-in widget tree inspector to identify memory leaks and fix them.

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final _myController = TextEditingController();

  @overridevoid dispose() {
    _myController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Memory Leak Example'),
      ),
      body: Center(
        child: TextField(
          controller: _myController,
        ),
      ),
    );
  }
}

Widget Tree Rebuilds In Flutter


The widget tree rebuilds every time the app's state changes. This can lead to performance issues if the widget tree is too complex. To avoid unnecessary widget tree rebuilds, developers can use the shouldRebuild() method in the shouldNotify() method of ChangeNotifier.


import 'package:flutter/material.dart';

class CounterModel extends ChangeNotifier {
  int _counter = 0;

  int get counter => _counter;

  void increment() {
    _counter++;
    // Use notifyListeners only when the state has actually changed
    notifyListeners();
  }

  // Override shouldNotify to prevent unnecessary widget rebuilds@override
  bool shouldNotify(CounterModel old) => old.counter != counter;
}

class MyHomePage extends StatelessWidget {
  final CounterModel counter = CounterModel();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('My App'),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          MyTextWidget(
            counter: counter,
          ),
          ElevatedButton(
            child: Text('Increment Counter'),
            onPressed: () {
              counter.increment();
            },
          ),
        ],
      ),
    );
  }
}

class MyTextWidget extends StatelessWidget {
  final CounterModel counter;

  const MyTextWidget({Key key, this.counter}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Text('Counter: ${counter.counter}');
  }
}

In this example, we've created a CounterModel class that extends ChangeNotifier and contains a counter value. We've overridden the shouldNotify method to prevent unnecessary widget rebuilds when the counter value changes.


The shouldNotify method is called by the framework every time a ChangeNotifier's notifyListeners method is called. It takes an old ChangeNotifier object as an argument and returns true if the widget should be rebuilt or false if the widget should not be rebuilt.


In this case, we're checking if the counter value of the old and new objects is the same. If it's different, we return true to indicate that the widget should be rebuilt. If it's the same, we return false to indicate that the widget should not be rebuilt.


By using the shouldNotify method to prevent unnecessary widget rebuilds, you can improve the performance of your Flutter app and reduce the amount of unnecessary work the framework has to do.


Image Caching Issues


Flutter uses an image caching mechanism to improve app performance by caching images locally. However, this can lead to issues if the images are not disposed of properly, leading to memory leaks and other performance issues.


To avoid image caching issues, developers can use the precacheImage() method to cache images before they are needed. Developers can also use the imageCache.clear(); method to clear the image cache when it's no longer needed.


class MyImage extends StatelessWidget {
  final String imageUrl;

  const MyImage({Key key, @required this.imageUrl}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    // Precache the image before it is displayed
    precacheImage(NetworkImage(imageUrl), context);

    return Image.network(imageUrl);
  }
}

// To clear the image cache, use the clearCache() methodclass MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('My App'),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text('Clear Image Cache'),
          onPressed: () {
            // Clear the image cache
            imageCache.clear();
          },
        ),
      ),
    );
  }
}

Inefficient Animations


Animations can make Flutter apps visually appealing but can also impact app performance if not optimized properly. Inefficient animations can lead to jank and lag, especially on lower-end devices.


To optimize animations in Flutter, developers can use the AnimatedBuilder widget to build animations efficiently. Developers can also use the TickerProviderStateMixin to synchronize animations with the app's frame rate, reducing jank and lag.

class MyAnimation extends StatefulWidget {
  @override
  _MyAnimationState createState() => _MyAnimationState();
}

class _MyAnimationState extends State<MyAnimation>
    with SingleTickerProviderStateMixin {
  AnimationController _controller;

  @overridevoid initState() {
    super.initState();
    _controller = AnimationController(
      duration: const Duration(seconds: 1),
      vsync: this,
    )..repeat(reverse: true);
  }

  @overridevoid dispose() {
    _controller.dispose();
    super.dispose();
  }

  @overrideWidget build(BuildContext context) {
    return AnimatedBuilder(
      animation: _controller,
      builder: (BuildContext context, Widget child) {
        return Transform.rotate(
          angle: _controller.value * 2.0 * math.pi,
          child: child,
        );
      },
      child: Container(
        width: 200.0,
        height: 200.0,
        color: Colors.blue,
      ),
    );
  }
}


Conclusion


Flutter is a powerful and efficient framework for building cross-platform apps. However, like any other technology, it has its own set of bugs and issues that developers need to be aware of.


By using proper state management techniques, disposing of objects properly, avoiding unnecessary widget tree rebuilds, optimizing image caching, and using efficient animations, developers can build high-performance Flutter apps that provide a great user experience.


Blog for Mobile App Developers, Testers and App Owners

 

This blog is from Finotes Team. Finotes is a lightweight mobile APM and bug detection tool for iOS and Android apps.

In this blog we talk about iOS and Android app development technologies, languages and frameworks like Java, Kotlin, Swift, Objective-C, Dart and Flutter that are used to build mobile apps. Read articles from Finotes team about good programming and software engineering practices, testing and QA practices, performance issues and bugs, concepts and techniques. 

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