SystemNavigator.pop() causes Amplify exception

[wasitu]

Describe the bug
Flutter's SystemNavigator.pop() causes Amplify exception by starting app again.
(Using android's back button for closing app causes the same problem)

To Reproduce
Steps to reproduce the behavior:

1. Configure Amplify like

final amplify = Amplify();
amplify.addPlugin(authPlugins: [AmplifyAuthCognito()]);
await amplify.configure('~~~')

2. Use SystemNavigator.pop() for close app on root page (or press android's back button)
3. Start app again
4. You can see error on logcat

Platform
Amplify Flutter current supports iOS and Android. This issue is reproducible in (check all that apply):
[×] Android
[] iOS

Smartphone (please complete the following information):

• Device: Pixel 4a
• OS: 11
• Flutter: 1.22.0 (stable)

[fjnoyp]

Hi @wasitu this issue appears to be related to a previously closed issue - the root cause is from how the Flutter framework behaves:

#99

Please see the workarounds suggested in the issue as a possible solution for your problem:

This seems like an issue where the back button causes the FlutterActivity to be destroyed in Android instead of sending it to background. There are some workarounds mentioned here https://stackoverflow.com/questions/55539302/sending-your-application-to-background-when-back-button-is-pressed-in-flutter that can be used by the applications such as

https://medium.com/stuart-engineering/%EF%B8%8F-the-tricky-task-of-keeping-flutter-running-on-android-2d51bbc60882
https://www.programmersought.com/article/3839440802/

[wasitu]

@fjnoyp
Thanks for your reply.

Yeah, I saw those workaround but I think its not that.
Because If I remove Amplify, Everything fine. (Behavior seems to be restarted all and can use other libraries.)

[fjnoyp]

Ah I see @wasitu. Could you provide the full error log you're getting here? Does keeping a bool isConfigured and only calling configure() if it's false fix your problem?

[wasitu]

@fjnoyp
Here's log

W/GeneratedPluginsRegister( 9410): Tried to automatically register plugins with FlutterEngine (io.flutter.embedding.engine.FlutterEngine@ecc66fc) but could not find and invoke the GeneratedPluginRegistrant.

E/flutter ( 9410): [ERROR:flutter/lib/ui/ui_dart_state.cc(177)] Unhandled Exception: MissingPluginException(No implementation found for method configure on channel com.amazonaws.amplify/core)
E/flutter ( 9410): #0      MethodChannel._invokeMethod
package:flutter/…/services/platform_channel.dart:157
E/flutter ( 9410): <asynchronous suspension>
E/flutter ( 9410): #1      MethodChannel.invokeMethod
package:flutter/…/services/platform_channel.dart:332
E/flutter ( 9410): #2      MethodChannelAmplifyCore.configure
package:amplify_core_plugin_interface/method_channel_amplify.dart:25
E/flutter ( 9410): #3      Amplify.configure
package:amplify_core/amplify_core.dart:71
E/flutter ( 9410): #4      setup
package:myapp/main.dart:47
E/flutter ( 9410): #5      main
package:myapp/main.dart:24
E/flutter ( 9410): #6      _runMainZoned.<anonymous closure>.<anonymous closure> (dart:ui/hooks.dart:231:25)
E/flutter ( 9410): #7      _rootRun (dart:async/zone.dart:1190:13)
E/flutter ( 9410): #8      _CustomZone.run (dart:async/zone.dart:1093:19)
E/flutter ( 9410): #9      _runZoned (dart:async/zone.dart:1630:10)
E/flutter ( 9410): #10     runZonedGuarded (dart:async/zone.dart:1618:12)
E/flutter ( 9410): #11     _runMainZoned.<anonymous closure> (dart:ui/hooks.dart:223:5)
E/flutter ( 9410): #12     _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:301:19)
E/flutter ( 9410): #13     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)

bool isConfigured can't fix problem. Since Dart seems to be reset, it's always false.
As log said, Automatically registration plugins failed with amplify one.

[wasitu]

I fixed it temporally like this.
https://github.com/wasitu/amplify-flutter/commit/80e9eb6ef058e2d8e49ea2b093c489c8739e90fc

But I dont have much time (and smart brain) to test and think if it's ok or not. Just working for me.

[brunovsiqueira]

I'm having the exact same issue mentioned by @wasitu.

[Rayv1]

Hi guys,
i had the same Problem and i had to implement the "check-if-amplify-configured"-Fix and the from @fjnoyp mentioned FlutterActivity Workaround from StackOverflow

Its working now independently from how the app is closed.

[brunovsiqueira]

@Rayv1 I found different solutions in the link you provided. Which solution worked for you?

[Rayv1]

This Solution worked:
var _androidAppRetain = MethodChannel("android_app_retain");

@override
Widget build(BuildContext context) {
return WillPopScope(
  onWillPop: () {
    if (Platform.isAndroid) {
      if (Navigator.of(context).canPop()) {
        return Future.value(true);
      } else {
        _androidAppRetain.invokeMethod("sendToBackground");
        return Future.value(false);
      }
    } else {
      return Future.value(true);
    }
  },
  child: Scaffold(
    ...
  ),
);

The code in the MainActivity() should look like this:

class MainActivity: FlutterActivity() {

override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
    GeneratedPluginRegistrant.registerWith(flutterEngine);

    MethodChannel(flutterEngine.dartExecutor.binaryMessenger, "android_app_retain").apply {
        setMethodCallHandler { method, result ->
            if (method.method == "sendToBackground") {
                moveTaskToBack(true)
            }
        }
    }
}
}

[brunovsiqueira]

Hi guys. I tried the above solution and it seems to work in the back pressed case but it still causes crashes on Crashlytics.

@Amplifiyer is there any schedule to have this bug fixed? In my opinion it is a really important bug because it crashes the app.

[Amplifiyer]

The original issue with MissingPluginException has been fixed in #345 Please see #99 for more details about this issue. Closing as duplicate. The fix will be available in our next release.