FlutterFragment is not retaining state - flutter

Question

I am trying to embed a Flutter app inside my existing Android app using this steps:
https://github.com/flutter/flutter/wiki/Add-Flutter-to-existing-apps
I am embedding the FlutterFragment inside my Activity in onCreate method, but when I rotate the screen, the fragment does not retain it's state.
This is MainActivity code:
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
if (savedInstanceState == null) {
supportFragmentManager.beginTransaction().also {
it.replace(android.R.id.content, Flutter.createFragment(null), "flutter")
}.commit()
} else {
val flutterFragment = supportFragmentManager.findFragmentByTag("flutter")
supportFragmentManager.beginTransaction().also {
it.attach(flutterFragment!!)
}.commit()
}
}
}

Answer 1

You are probably not declaring your Activity properly. The configChanges are very important for Flutter to work with Android's lifecycle.
You have to declare it on the AndroidManifest like this:
<activity
android:launchMode="singleTop"
android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density"
android:hardwareAccelerated="true"
android:windowSoftInputMode="adjustResize"
android:name=".MainActivity"
android:theme="#style/AppTheme.NoActionBar"/>