App crashes on Android when flutter is reattached to engine

[yanivshaked]

Description
A crash occurs on Android when flutter is reattached to engine.

Expected behavior
There should not be any crash.

Current behavior
Application crashes.

To Reproduce
Steps to reproduce the crash:

1. Run an app
2. Detach FlutterFragment from FlutterEngine
3. Attach FlutterFragment to FlutterEngine

Logs

E/AndroidRuntime(12175): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'io.flutter.plugin.common.BinaryMessenger io.flutter.embedding.engine.plugins.FlutterPlugin$FlutterPluginBinding.getBinaryMessenger()' on a null object reference
E/AndroidRuntime(12175):        at com.arthenica.ffmpegkit.flutter.FFmpegKitFlutterPlugin.onAttachedToActivity(FFmpegKitFlutterPlugin.java:196)
E/AndroidRuntime(12175):        at io.flutter.embedding.engine.FlutterEngineConnectionRegistry.attachToActivityInternal(FlutterEngineConnectionRegistry.java:362)
E/AndroidRuntime(12175):        at io.flutter.embedding.engine.FlutterEngineConnectionRegistry.attachToActivity(FlutterEngineConnectionRegistry.java:344)
E/AndroidRuntime(12175):        at io.flutter.embedding.android.FlutterActivityAndFragmentDelegate.onAttach(FlutterActivityAndFragmentDelegate.java:176)
E/AndroidRuntime(12175):        at io.flutter.embedding.android.FlutterActivity.onCreate(FlutterActivity.java:430)
E/AndroidRuntime(12175):        at android.app.Activity.performCreate(Activity.java:8006)
E/AndroidRuntime(12175):        at android.app.Activity.performCreate(Activity.java:7990)
E/AndroidRuntime(12175):        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1329)
E/AndroidRuntime(12175):        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3595)

Environment

• Platform: Android
• Flutter Version (if applicable) 2.5.3
• Source branch (if applicable) development-flutter
• Android Studio version (if applicable) 2020.3

Other
Solution should be not to call flutterPluginBinding = null; from onDetachedFromActivity, but to call it from onDetachedFromEngine.

[tanersener]

We haven't tested the plugin in an app which uses fragments. It seems like something is wrong there. I'll approve the PR when it passes the PR checks. Thanks for reporting this.

[yanivshaked]

Thanks. I will close this issue as soon as a new ffmpeg-kit version is released.

[tanersener]

Fixed in v4.5.1.