root_overlay_injector.dart

import 'package:flutter/material.dart';

class RootOverlayInjector extends Overlay {
  final Widget child;

  const RootOverlayInjector({Key key, this.child})
      : super(key: key, initialEntries: const []);

  @override
  _RootOverlayInjectorState createState() => _RootOverlayInjectorState();
}

class _RootOverlayInjectorState extends OverlayState {
  @override
  BuildContext get context =>
      super.context.findRootAncestorStateOfType<OverlayState>().context;

  @override
  Widget build(BuildContext context) => (widget as RootOverlayInjector).child;
}