import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  State<MyApp> createState() => MyAppState();
}

class MyAppState extends State<MyApp> {
  Color _color = Colors.green;

  @override
  Widget build(BuildContext context) {
    return InheritedColor(
      color: Colors.red,
      child: MaterialApp(
        home: Scaffold(
          body: ListView(
            children: <Widget>[
              InheritedColor(
                color: _color,
                child: Test(),
              ),
              ListTile(
                title: Text('Blue'),
                onTap: () { setState(() { _color = Colors.blue; }); },
              ),
              ListTile(
                title: Text('Green'),
                onTap: () { setState(() { _color = Colors.green; }); },
              ),
              ListTile(
                title: Text('Teal'),
                onTap: () { setState(() { _color = Colors.teal; }); },
              ),
            ],
          ),
        ),
      ),
    );
  }
}

class Test extends StatefulWidget {
  Test();

  State<Test> createState() => _TestState();
}

class _Card {
  _Card(this.entry, this.widget);
  final ProxyOverlayEntry entry;
  final Widget widget;
}

class _TestState extends State<Test> {
  int _count = 0;

  static const double dim = 100.0;

  Set<_Card> _cards = <_Card>{};

  @override
  Widget build(BuildContext context) {
    Widget result = ListTile(
      title: Text('Create Entry'),
      onTap: () {
        int index = _count;
        _count += 1;
        _Card card;
        card = _Card(
          ProxyOverlayEntry(),
          Builder(
            builder: (BuildContext context) {
              final Size size = MediaQuery.of(context).size;
              return Align(
                alignment: Alignment.topLeft,
                child: Padding(
                  padding: EdgeInsets.only(
                    left: dim * (index % (size.width ~/ dim)),
                    top: 200.0 + dim * ((index ~/ (size.width ~/ dim)) % ((size.height - 200.0) ~/ dim)),
                  ),
                  child: SizedBox(
                    width: dim,
                    height: dim,
                    child: Padding(
                      padding: EdgeInsets.all(10.0),
                      child: RaisedButton(
                        color: InheritedColor.of(context),
                        child: Text('#$index'),
                        onPressed: () {
                          card.entry.remove();
                          setState(() {
                            _cards.remove(card);
                          });
                        },
                      ),
                    ),
                  ),
                ),
              );
            },
          )
        );
        setState(() {
          _cards.add(card);
        });
        Overlay.of(context).insert(card.entry);
      },
    );
    for (_Card card in _cards) {
      result = OverlayConduit(
        key: ObjectKey(card),
        overlayEntry: card.entry,
        overlayChild: card.widget,
        child: result,
      );
    }
    return result;
  }
}

class InheritedColor extends InheritedWidget {
  InheritedColor({ this.color, Widget child }) : super(child: child);
  final Color color;
  @override
  bool updateShouldNotify(InheritedColor old) => old.color != color;

  static Color of(BuildContext context) {
    return (context.inheritFromWidgetOfExactType(InheritedColor) as InheritedColor).color;
  }
}