As a mobile developer, I’ve faced countless bugs. Some are minor UI glitches, while others are app-crashing nightmares that leave users frustrated. I want to share one such experience where a seemingly simple bug in a mobile app almost derailed an entire release—and how I fixed it.
The Bug: App Crashes on Launch for Some Users
A few months ago, I was working on a Flutter-based e-commerce app. During testing, everything worked fine on simulators and my devices—but when beta users tried the app on certain Android devices, it crashed immediately after tapping the icon.
No error messages appeared on the home screen, and the crash reports were inconsistent—sometimes only appearing on devices running Android 12+.
Step 1: Reproduce the Issue
The first step in any bug fix is reproducing the problem reliably.
I set up multiple emulators with the same Android versions as the affected devices.
Installed the app on real devices running Android 12 and 13.
Observed the crash pattern: it only occurred when the app tried to initialize the local database and fetch remote configuration from Firebase on launch.
By reproducing the bug, I could now trace where the crash was happening instead of guessing.
Step 2: Investigate the Logs
Next, I connected the affected devices to Android Studio and used Logcat to inspect runtime errors.
Here’s what I found in the logs:
E/flutter (12345): MissingPluginException(No implementation found for method Firebase#initialize on channel ...)
E/AndroidRuntime(12345): java.lang.NullPointerException: Attempt to invoke virtual method on a null object reference
Ah! It was a plugin initialization issue. In Flutter, some Firebase plugins require explicit initialization before you use them. On newer Android versions, the app was trying to access Firebase before the Flutter engine fully initialized.
Step 3: Identify the Root Cause
After reviewing the code, I realized:
I had Firebase initialization code in the main widget’s initState() instead of the entry point main() function.
Some devices executed initState() before the plugin was ready, leading to a crash.
The crash only happened on newer OS versions due to slight changes in plugin loading behavior.
This is a classic timing/initialization bug that is tricky to catch in simulators because most emulators load faster than real devices.
Step 4: Fix the Bug
Here’s the fix I implemented:
void main() async {
WidgetsFlutterBinding.ensureInitialized(); // Ensures Flutter engine is ready
await Firebase.initializeApp(); // Initialize Firebase before runApp
runApp(MyApp());
}
Key points:
WidgetsFlutterBinding.ensureInitialized() ensures the Flutter engine is fully initialized before any async operations.
await Firebase.initializeApp() guarantees Firebase is ready before any widget tries to access it.
Removed all Firebase initialization from initState() in widgets—so nothing runs prematurely.
Step 5: Test Thoroughly
After implementing the fix:
Tested on all affected Android versions (12 and 13).
Verified on older versions (10 and 11) to ensure backward compatibility.
Checked iOS devices—Firebase initialization worked correctly without crashes.
The crash was gone, and users could open the app reliably.
Lessons Learned
Always initialize plugins in the entry point if they are required on launch.
Reproduce bugs on real devices, not just emulators. Timing and OS-specific behavior often differ.
Logs are your best friend. Logcat, Xcode console, and crash reporting tools (like Firebase Crashlytics) save hours of debugging.
Async operations on startup need careful handling—never assume plugins are ready inside initState().
Closing Thoughts
Bugs like this are frustrating—but they also teach you to anticipate edge cases and write more resilient apps. By focusing on reproduction, logs, and step-by-step debugging, even the most elusive crashes can be fixed.
If you’re shipping mobile apps, take this to heart: initialization order matters, especially with plugins and async operations. It can be the difference between a smooth user experience and a crashing app.
Top comments (0)