Cannot access 'android.arch.lifecycle.LifecycleOwner' which is a supertype of 'com.ex.app.MainActivity'
I face same Problem, now it solved in my case
Step 1 : open your project in AndroidStudio
Step 2 : open Terminal and goto your project path in terminal
Step 3 : Hit this command 'git clean -xfd'
Step 3 : Goto : File -> Invalidate caches/restart
You need to go to the flutter directory
rm -rf bin/cache/artifacts/engine/android*Then go to project directory
flutter cleanflutter pub getAlso you can "Invalidate caches and restart" in Android Studio.
You need to enable the beta feature "Enable code completion, navigation, etc. for Java / Kotlin" at: Preferences -> Languages & Frameworks -> Flutter (bottom).