App crashes are one of the most frustrating problems in user experience and can significantly decrease user retention. There are 4 main reasons why crashes may happen in Flutter:

  • Memory Leaks;
  • Unhandled Exceptions;
  • Platform-Specific Issues;
  • Hardware Limitations.

In this article, we will dive deeper into the these reasons and provide practical solutions to address each issue.

Reason 1: Memory Leaks

Memory leaks occur when a program fails to release unused memory, causing a gradual increase in memory usage. Here are reasons why leaks may happen and how to fix them:

Unreleased Resources

Resources such as streams, animations, or file handles are not properly disposed of, leading to memory leaks.

How to fix:

💡
Always call dispose() method to release resources in your State classes.
💡
Use AutomaticKeepAliveClientMixin with caution, ensuring wantKeepAlive is set correctly.

Retaining State Objects

Retaining state objects that are no longer needed can cause memory leaks.

How to fix:

💡
Use StatefulWidget judiciously and dispose of any controllers, listeners, or other state-related objects in the dispose() method.
💡
Ensure you remove any listeners or callbacks in the dispose() method.

Improper Use of Global Keys

GlobalKeys can keep references to widgets and their states, which can lead to memory leaks if not handled correctly.

How to fix:

💡
Use GlobalKeys sparingly and only when necessary.
💡
Ensure GlobalKeys are properly disposed of or replaced when the widget tree changes significantly.

Static References

Holding onto static references to context or widgets can prevent the garbage collector from reclaiming memory.

How to fix:

💡
Avoid using static references to contexts or widgets.
💡
Use dependency injection or state management solutions (like Provider, Riverpod, etc.) that do not rely on static references.

Circular References

Circular references between objects can prevent garbage collection.

How to fix:

💡
Break circular dependencies by ensuring there are no strong references forming a loop.
💡
Use WeakReference or other mechanisms to avoid strong references when appropriate.

Event Listeners and Subscriptions

Event listeners or subscriptions that are not canceled can lead to memory leaks.

How to fix:

💡
Always cancel event listeners and subscriptions in the dispose() method.
💡
Use a StreamController with broadcast for multiple listeners, and ensure to close the controller.

Asynchronous Operations

Async operations holding onto context or state can cause memory leaks if not handled properly.

How to fix:

💡
Use mounted property to check if the widget is still in the widget tree before updating the state after an asynchronous operation.
💡
Ensure long-running async operations do not hold onto unnecessary references.

Inappropriate Use of Context

Retaining references to context or using InheritedWidgets improperly can cause memory leaks.

How to fix:

💡
Be cautious with context usage, and ensure contexts do not outlive their intended lifecycle.
💡
Use state management libraries to manage state effectively without over-relying on InheritedWidgets.
To detect and resolve memory leaks, use Dart DevTools' Memory View.

Reason 2: Unhandled Exceptions

Unhandled exceptions are another common reason why a Flutter app may crash. Here are 3 recommendations that will make your app more stable:

Analyze Common Error Sources

There are some common sources of unhandled exceptions that Flutter engineers skip more often compared to the rest. For example:

  • Out of Range Errors: Occur when accessing an invalid index in a list or array.
  • Asynchronous Errors: Happen during network calls, file I/O operations, and other async tasks if not properly managed.
  • Third-Party Libraries: Can introduce unexpected exceptions, especially if not well-maintained or compatible with the Flutter version.
💡
Try to analyze your code for those weak places to make sure everything is handled correctly.

Use Global Error Handler

In Flutter, global error handler is a special technique to catch exceptions in the widget tree and prevent them from causing the entire app to crash. Here is an example:

void main() {
 FlutterError.onError = (FlutterErrorDetails details) {
   FlutterError.dumpErrorToConsole(details);
   // Custom error handling logic
 };

 runApp(MyApp());
}
💡
Use a global error handler to make sure that unexpected errors in the widget tree are caught and managed appropriately.

Integrate Logging and Monitoring

Proactive monitoring and logging are important for identifying and resolving exceptions that are caught in production. The most popular tool solving the problem is Firebase Crashlytics.

Firebase Crashlytics
Get clear, actionable insight into app issues with this powerful crash reporting solution for Apple, Android, Flutter, and Unity.
Firebase

Firebase Crashlytics works quite simply: you set up the library in your code, and whenever an error occurs in the production app, you can see it along with all the details in the dashboard with the ability to effectively group, break down, filter, and analyze records.

💡
Integrate Firebase Crashlytics in your application to monitor and manage exceptions in production.

Reason 3: Platform-Specific Issues

Although you may have covered all possible problems in your Dart code, issues in the native parts can still cause your Flutter app to crash.

Unconsidered Differences

Differences in how different platforms handle certain functionalities can lead to crashes if not properly addressed. Examples include variations in permission handling, file system paths, and more.

💡
Analyze your code for possible unconsidered differences and use conditional statements to execute different code depending on the platform the app is running on.
String getFilePath() {
  if (Platform.isIOS) {
    return 'iOS-specific-path';
  } else if (Platform.isAndroid) {
    return 'Android-specific-path';
  } else if (Platform.isWindows) {
    return 'Windows-specific-path';
  }
  return 'default-path';
}

// We recommend to use "path" package

Exceptions in Native Code

Native code (Kotlin for Android, Swift for iOS and macOS, C++ for Windows, and so on) integrated into the Flutter app can throw exceptions that lead to crashes. Common issues include incorrect method calls, null pointer exceptions, and improper handling of native resources.

💡
Debug native code separately or simultaneously with Dart code using a native language debugger.

Reason 4: Hardware Limitations

Even if you have covered all the cases in your Dart and native code, ensuring everything works perfectly, there is still a chance that your app will crash due to hardware limitations.

Memory Limitations

Some devices may struggle to handle large images, videos, or audio features like:

  • Loading many high-resolution images on the same page;
  • Playing multiple video streams or switching between them;
  • Processing large audio, video or 3D files.

These tasks can quickly consume available memory, causing the app to crash, especially on hardware with lower RAM capacities.

💡
Optimize your media file loading, use compressed formats, and keep as few media instances as possible on the same page.
💡
To profile memory usage, use Dart DevTools' Memory View.

CPU Limitations

Devices with slower processors may struggle to handle complex computations or tasks, leading to app crashes. Examples of such issues include:

  • Processing data from sensors (e.g., accelerometer, gyroscope) in real-time for fitness or navigation apps.
  • Running machine learning models on-device for tasks like image recognition or language translation.
  • Processing and analyzing large datasets, such as sorting large lists or performing complex database queries.
  • Applying filters, effects, and transformations to images and videos in real-time.
💡
Break down complex tasks into smaller, manageable chunks. Optimize computation algorithms.
💡
Move tasks to the background, as different OS allow such an ability.

Storage Limitations

Devices with insufficient storage space may face issues when saving large files or handling significant amounts of data, leading to app crashes. Examples include running out of disk space when saving large files or handling extensive data caching.

💡
Check available storage space before performing operations that require significant storage.
💡
Implement data cleaning routines to remove unnecessary files and data periodically.

Conclusion

We explored the main reasons why Flutter apps may crash: Memory Leaks, Unhandled Exceptions, Platform-Specific Issues, and Hardware Limitations. Addressing these issues is crucial for ensuring a smooth user experience and high retention rate.

At What the Flutter, we love working with Flutter apps to make them more stable and delightful for users. Contact us to discuss how we can help with your app crashes or any other technical issues. You can also discover full list of Flutter services we provide. Let your app be awesome!

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