InformationFragment.kt

package <your.package.name>

// import statements
// ...

class InformationFragment : BaseFragment() {

    // class and instance variables...

    companion object {
        private const val TAG_FLUTTER_FRAGMENT = "flutter_fragment"
    }
    private var flutterFragment: FlutterFragment? = null

    // other functions...

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Fragmentをinflateするのは割愛
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        // extensionで定義された関数を使用
        flutterFragment = createFlutterFragment(TAG_FLUTTER_FRAGMENT, "informationTabFlutterEngine", R.id.information_futter_fragment)
    }

    override fun onCreateOptionsMenu(menu: Menu, menuInflater: MenuInflater) {
        // menuのinflateは割愛
    }

    override fun onAttachFragment(childFragment: Fragment) {
        super.onAttachFragment(childFragment)
        pushToFlutterFragment(childFragment, flutterFragment, "/information") // フラターアプリ内でrouteをプッシュして特定の画面を出します
    }
}