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{# This content gets published to the following location: #} {# https://firebase.google.com/docs/crashlytics/customize-crash-reports?platform=flutter #}

This guide describes how to customize your crash reports using {{crashlytics}} APIs. By default, {{crashlytics}} automatically collects platform-native crash reports for all your app's users (you can also turn off automatic crash reporting and enable opt-in reporting for your users instead). {{crashlytics}} provides five logging mechanisms out of the box: custom keys, custom logs, user identifiers, caught and uncaught exceptions.

For Flutter apps, fatal reports are sent to {{crashlytics}} in real-time without the need for the user to restart the application. Non-fatal reports are written to disk to be sent along with the next fatal report or when the app restarts.

Report uncaught exceptions {: #report-uncaught-exceptions}

You can automatically catch all errors that are thrown within the Flutter framework by overriding FlutterError.onError with FirebaseCrashlytics.instance.recordFlutterFatalError:

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  await Firebase.initializeApp();

  // Pass all uncaught errors from the framework to Crashlytics.
  FlutterError.onError = FirebaseCrashlytics.instance.recordFlutterFatalError;

  runApp(MyApp());
}

Zoned errors {: #zoned-errors}

Not all errors are caught by Flutter. Sometimes, errors are instead caught by Zones. A common case where relying on Flutter to catch errors would not be enough is when an exception happens inside the onPressed handler of a button:

ElevatedButton(
  onPressed: () {
    throw Error();
  }
  ...
)

To catch such errors, you can use runZonedGuarded:

void main() async {
  runZonedGuarded<Future<void>>(() async {
    WidgetsFlutterBinding.ensureInitialized();
    await Firebase.initializeApp();
    // The following lines are the same as previously explained in "Handling uncaught errors"
    FlutterError.onError = FirebaseCrashlytics.instance.recordFlutterFatalError;

    runApp(MyApp());
  }, (error, stack) => FirebaseCrashlytics.instance.recordError(error, stack, fatal: true));
}

Note: You must call WidgetsFlutterBinding.ensureInitialized() inside runZonedGuarded. Error handling wouldn’t work if WidgetsFlutterBinding.ensureInitialized() was called from the outside.

Errors outside of Flutter {: #errors-outside-flutter}

To catch errors that happen outside of the Flutter context, install an error listener on the current Isolate:

Isolate.current.addErrorListener(RawReceivePort((pair) async {
  final List<dynamic> errorAndStacktrace = pair;
  await FirebaseCrashlytics.instance.recordError(
    errorAndStacktrace.first,
    errorAndStacktrace.last,
    fatal: true,
  );
}).sendPort);

Report caught exceptions {: #report-caught-exceptions}

In addition to automatically reporting your app’s crashes, {{crashlytics}} lets you record non-fatal exceptions and sends them to you the next time a fatal event is reported or when the app restarts.

Note: {{crashlytics}} only stores the most recent eight recorded non-fatal exceptions. If your app throws more than eight, older exceptions are lost. This count is reset each time a fatal exception is thrown, since this causes a report to be sent to {{crashlytics}}.

Use the recordError method to record non-fatal exceptions in your app's catch blocks. For example:

await FirebaseCrashlytics.instance.recordError(
  error,
  stackTrace,
  reason: 'a non-fatal error'
);

You may also wish to log further information about the error which is possible using the information property:

await FirebaseCrashlytics.instance.recordError(
  error,
  stackTrace,
  reason: 'a non-fatal error',
  information: ['further diagnostic information about the error', 'version 2.0'],
);

Warning: If you want to include a unique value (for example, a user ID or a timestamp) in your exception message, use a custom key instead of adding the value directly in the exception message. Adding values directly can result in several issues and may cause {{crashlytics}} to limit reporting errors in your app.

These exceptions appear as non-fatal issues in the {{name_appmanager}}. The issue summary contains all the state information you normally get from crashes, along with breakdowns by version and hardware device.

{{crashlytics}} processes exceptions on a dedicated background thread to minimize the performance impact to your app. To reduce your users’ network traffic, {{crashlytics}} will rate-limit the number of reports sent off device, if necessary.

Add custom keys {: #add-keys}

Custom keys help you get the specific state of your app leading up to a crash. You can associate arbitrary key/value pairs with your crash reports, then use the custom keys to search and filter crash reports in the {{name_appmanager}}.

  • In the {{crashlytics}} dashboard{:.external}, you can search for issues that match a custom key.

  • When you're reviewing a specific issue in the console, you can view the associated custom keys for each event (Keys subtab) and even filter the events by custom keys (Filter menu at the top of the page).

Note: {{crashlytics}} supports a maximum of 64 key/value pairs. After you reach this threshold, additional values are not saved. Each key/value pair can be up to 1 kB in size.

Use the setCustomKey instance method to set key/value pairs. Here are some examples:

// Set a key to a string.
FirebaseCrashlytics.instance.setCustomKey('str_key', 'hello');

// Set a key to a boolean.
FirebaseCrashlytics.instance.setCustomKey("bool_key", true);

// Set a key to an int.
FirebaseCrashlytics.instance.setCustomKey("int_key", 1);

// Set a key to a long.
FirebaseCrashlytics.instance.setCustomKey("int_key", 1L);

// Set a key to a float.
FirebaseCrashlytics.instance.setCustomKey("float_key", 1.0f);

// Set a key to a double.
FirebaseCrashlytics.instance.setCustomKey("double_key", 1.0);

Add custom log messages {: #add-logs}

To give yourself more context for the events leading up to a crash, you can add custom {{crashlytics}} logs to your app. {{crashlytics}} associates the logs with your crash data and displays them in the {{name_appmanager}}{: .external}, under the {{crashlytics}} Logs tab.

Note: To avoid slowing down your app, {{crashlytics}} limits logs to 64kB and deletes older log entries when a session's logs go over that limit.

Use log to help pinpoint issues. For example:

FirebaseCrashlytics.instance.log("Higgs-Boson detected! Bailing out");

Set user identifiers {: #set-user-ids}

To diagnose an issue, it’s often helpful to know which of your users experienced a given crash. {{crashlytics}} includes a way to anonymously identify users in your crash reports.

To add user IDs to your reports, assign each user a unique identifier in the form of an ID number, token, or hashed value:

FirebaseCrashlytics.instance.setUserIdentifier("12345");

If you ever need to clear a user identifier after you set it, reset the value to a blank string. Clearing a user identifier does not remove existing {{crashlytics}} records. If you need to delete records associated with a user ID, contact Firebase support.

Enable opt-in reporting {: #enable-reporting}

By default, {{crashlytics}} automatically collects crash reports for all your app's users. To give users more control over the data they send, you can enable opt-in reporting by disabling automatic reporting and only sending data to {{crashlytics}} when you choose to in your code:

  1. Turn off automatic collection natively:

    Apple platforms

    Add a new key to your Info.plist file:

    • Key: FirebaseCrashlyticsCollectionEnabled
    • Value: false

    Android

    In the application block of your AndroidManifest.xml file, add a meta-data tag to turn off automatic collection:

    <meta-data
    android:name="firebase_crashlytics_collection_enabled"
    android:value="false" />

  2. Enable collection for select users by calling the {{crashlytics}} data collection override at runtime.

    The override value persists across launches of your app so {{crashlytics}} can automatically collect reports. To opt out of automatic crash reporting, pass false as the override value. When set to false, the new value does not apply until the next run of the app.

    FirebaseCrashlytics.instance.setCrashlyticsCollectionEnabled(true);

Note: When data collection is disabled, {{crashlytics}} will store crash information locally on the device. If data collection is subsequently enabled, any crash information stored on the device will be sent to {{crashlytics}} for processing.