fix: issue #265

[lcor-io]

Should fix the problem raised in issue #265

On Android, while disposing of the platform view, Mapbox tries to access Lifecycle events from the attached Activity. Problem is that this Activity could already be disposed of if the App where killed, with a back button for instance.
Checking if the activity is still registered should avoid Null Exceptions on those lifecycle callbacks.

[m0nac0]

Thank you for the contribution, I'd just like to wait for feedback from @tobrun whether we should actually return immediately if registrar.activity()==null or whether we can e.g. still safely call onDestroy() for the annotation managers.

[tobrun]

Problem is that this Activity could already be disposed of if the App where killed, with a back button for instance.

I haven't been able to reproduce the issue. The use-case is having a single page app that hosts a map and you use back button to kill the app?

[zhangxinagjunHJH]

@tobrun I created a flutter project, just show map and run app. it will crash when we try to use back button to exist app(try more than 5 times)

[m0nac0]

The docs for the new android plugin APIs (see #183 and https://flutter.dev/docs/development/packages-and-plugins/plugin-api-migration) explicitly mention registrar.activity() returning null and it being solved with the new APIs:

The new API has the advantage of providing a cleaner set of accessors for lifecycle dependent components compared to the old APIs. For instance PluginRegistry.Registrar.activity() could return null if Flutter isn’t attached to any activities.

So possibly this issue will also be solved if we migrate to the new plugin API.

[MATTYGILO]

Does this fix work?

[MATTYGILO]

com.mapbox.mapboxsdk.maps.Style.validateState (Style.java:777)
com.mapbox.mapboxsdk.maps.Style.getLayer (Style.java:240)
com.mapbox.mapboxsdk.location.SymbolLocationLayerRenderer.setLayerVisibility (SymbolLocationLayerRenderer.java:247)
com.mapbox.mapboxsdk.location.SymbolLocationLayerRenderer.hide (SymbolLocationLayerRenderer.java:109)
com.mapbox.mapboxsdk.location.LocationLayerController.hide (LocationLayerController.java:138)
com.mapbox.mapboxsdk.location.LocationComponent.disableLocationComponent (LocationComponent.java:1392)
com.mapbox.mapboxsdk.location.LocationComponent.setLocationComponentEnabled (LocationComponent.java:518)
com.mapbox.mapboxgl.MapboxMapController.dispose (MapboxMapController.java:806)
io.flutter.plugin.platform.VirtualDisplayController.dispose (VirtualDisplayController.java:171)
io.flutter.plugin.platform.PlatformViewsController.flushAllViews (PlatformViewsController.java:688)
io.flutter.plugin.platform.PlatformViewsController.onDetachedFromJNI (PlatformViewsController.java:570)
io.flutter.embedding.engine.FlutterEngine.destroy (FlutterEngine.java:361)
io.flutter.embedding.android.FlutterActivityAndFragmentDelegate.onDetach (FlutterActivityAndFragmentDelegate.java:522)
io.flutter.embedding.android.FlutterActivity.onDestroy (FlutterActivity.java:578)
android.app.Activity.performDestroy (Activity.java:8219)
android.app.Instrumentation.callActivityOnDestroy (Instrumentation.java:1342)
android.app.ActivityThread.performDestroyActivity (ActivityThread.java:5318)
android.app.ActivityThread.handleDestroyActivity (ActivityThread.java:5367)
android.app.servertransaction.DestroyActivityItem.execute (DestroyActivityItem.java:44)
android.app.servertransaction.TransactionExecutor.executeLifecycleState (TransactionExecutor.java:176)
android.app.servertransaction.TransactionExecutor.execute (TransactionExecutor.java:97)
android.app.ActivityThread$H.handleMessage (ActivityThread.java:2220)
android.os.Handler.dispatchMessage (Handler.java:107)
android.os.Looper.loop (Looper.java:237)
android.app.ActivityThread.main (ActivityThread.java:8016)
java.lang.reflect.Method.invoke (Method.java)
com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:493)
com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1076)

[MATTYGILO]

This needs to be implemented!!!!

[m0nac0]

I also haven't been able to reproduce this, but since it does seem fix an existing issue and shouldn't have any impact on anyone not affected by the issue, I'm going to approve this.

Thank you once again @leocornillon.

[christinachimi]

We're seeing similar errors causing crashes - curious if there is a timeline for releasing this?