[google_maps_flutter_web] Bad state: Cannot add new events after calling close (with fix proposed) #159388
Description
Steps to reproduce
This problem happens with all versions of google_maps_flutter_web, including the most recent one.
- create a Flutter web application using
google_maps_flutter, with a first page that opens a second page. This second page uses a GoogleMap widget. - pan around the map
- go back to the previous page.
This bug is difficult to reproduce, so you may have to insist quite a bit, but it does happen.
Expected results
No exception.
Actual results
In some rare circumstances, the following exception is raised:
DartError: Bad state: Cannot add new events after calling close
dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 296:3 throw_errors.dart:296
dart-sdk/lib/async/broadcast_stream_controller.dart 243:24 add broadcast_stream_controller.dart:243
packages/google_maps_flutter_web/src/google_maps_controller.dart 313:9 <fn> google_maps_controller.dart:313
dart-sdk/lib/async/zone.dart 1594:9 runUnaryGuarded zone.dart:1594
dart-sdk/lib/async/stream_impl.dart 365:5 [_sendData] stream_impl.dart:365
dart-sdk/lib/async/stream_impl.dart 541:13 perform stream_impl.dart:541
dart-sdk/lib/async/stream_impl.dart 646:10 handleNext stream_impl.dart:646
dart-sdk/lib/async/stream_impl.dart 617:7 callback stream_impl.dart:617
dart-sdk/lib/async/schedule_microtask.dart 40:11 _microtaskLoop schedule_microtask.dart:40
dart-sdk/lib/async/schedule_microtask.dart 49:5 _startMicrotaskLoop schedule_microtask.dart:49
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 181:7 <fn> async_patch.dart:181
A similar problem has been reported in the past here
As far as I can tell, there is nothing user code can do to prevent it from occuring. google_maps_flutter_web code has to be modified in the following way.
All the calls to listen() in _attachMapEvents should memorize the StreamSubscription return value in a member variable and then the stream subscriptions should be cancelled in the dispose() method of GoogleMapController.
In other words, we should have:
import 'package:google_maps/google_maps.dart' as gmaps;
[...]
class GoogleMapController {
[...]
// Add member variables
StreamSubscription<gmaps.MapMouseEventOrIconMouseEvent>? _subOnClick;
StreamSubscription<gmaps.MapMouseEvent>? _subOnRightClick;
StreamSubscription<void>? _subOnBoundsChanged;
StreamSubscription<void>? _subOnIdle;
void _attachMapEvents(gmaps.Map map) {
map.onTilesloaded.first.then((void _) {
// Report the map as ready to go the first time the tiles load
_streamController.add(WebMapReadyEvent(_mapId));
});
_subOnClick= map.onClick.listen((gmaps.MapMouseEventOrIconMouseEvent event) { ... });
// Do the same for all subscriptions
[...]
}and
void dispose() {
// Prior to closing the stream controller, cancel the subscriptions:
if (_subOnClick != null) {
_subOnClick!.cancel();
_subOnClick = null;
}
if (_subOnRightClick != null) {
_subOnRightClick!.cancel();
_subOnRightClick = null;
}
if (_subOnBoundsChanged != null) {
_subOnBoundsChanged!.cancel();
_subOnBoundsChanged = null;
}
if (_subOnIdle != null) {
_subOnIdle!.cancel();
_subOnIdle = null;
}
_widget = null;
_googleMap = null;
_circlesController = null;
_heatmapsController = null;
_polygonsController = null;
_polylinesController = null;
_markersController = null;
_clusterManagersController = null;
_tileOverlaysController = null;
_streamController.close();
}Note this is an easy, safe and reliable fix.
With the code as it is today, the stream controller may be closed and then, async event handlers may be called and the stream controller used again, raising the exception.
Usually, the exception is raised when in the onBoundsChanged handler.
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[√] Flutter (Channel stable, 3.24.3, on Microsoft Windows [version 10.0.22000.2538], locale fr-FR)
• Flutter version 3.24.3 on channel stable at C:\Users\andy\Documents\flutter
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[√] Android Studio (version 2022.3)
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• Flutter plugin can be installed from:
https://plugins.jetbrains.com/plugin/9212-flutter
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https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build 17.0.6+0-b2043.56-10027231)
[√] IntelliJ IDEA Community Edition (version 2021.3)
• IntelliJ at C:\Users\andy\Documents\Applications\IntelliJ
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[√] Connected device (3 available)
• Windows (desktop) • windows • windows-x64 • Microsoft Windows [version 10.0.22000.2538]
• Chrome (web) • chrome • web-javascript • Google Chrome 131.0.6778.86
• Edge (web) • edge • web-javascript • Microsoft Edge 131.0.2903.63
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• No issues found!