Cupertino ActionSheet

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(home: new BottomSheetColor()));
}

class BottomSheetColor extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: new AppBar(),
      floatingActionButton: Theme(
        data: Theme.of(context).copyWith(canvasColor: Colors.transparent),
        child: Builder(
          builder: (BuildContext context) {
            return new FloatingActionButton(
              onPressed: () {
                showModalBottomSheet<void>(
                    context: context,
                    builder: (BuildContext context) {
                      final List<String> items = <String>[
                        'Cancel',
                        'Item 1',
                        'Item 2',
                        'Item 3',
                      ];

                      return CupertinoActionSheet(
                        items: items,
                        onTap: (index) {
                          print(index);
                        },
                      );
                    });
              },
            );
          },
        ),
      ),
    );
  }
}

class CupertinoActionSheet extends StatelessWidget {
  CupertinoActionSheet({Key key, @required this.items, @required this.onTap})
      : assert(items.length > 1),
        super(key: key);

  final List<String> items;

  final void Function(int index) onTap;

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      bottom: true,
      child: Builder(
        builder: (BuildContext context) {
          final List<Widget> widgets = <Widget>[];

          final BoxDecoration boxDecoration = new BoxDecoration(
            color: Colors.white.withOpacity(.9),
            borderRadius: new BorderRadius.circular(8.0),
          );

          widgets.add(InkWell(
            onTap: () {
              onTap(0);
              Navigator.pop(context);
            },
            child: new Container(
              width: double.infinity,
              height: 48.0,
              margin: const EdgeInsets.symmetric(horizontal: 16.0).copyWith(top: 8.0),
              alignment: AlignmentDirectional.center,
              decoration: boxDecoration,
              child: new Text(
                items[0],
                style: const TextStyle(
                  fontWeight: FontWeight.w600,
                  fontSize: 18.0,
                  color: CupertinoColors.activeBlue,
                ),
              ),
            ),
          ));

          final List<String> remaining = items.sublist(1);

          widgets.add(new Container(
            width: double.infinity,
            alignment: AlignmentDirectional.center,
            margin: const EdgeInsets.symmetric(horizontal: 16.0),
            decoration: boxDecoration,
            child: new Column(
              children: remaining.fold(<Widget>[], (List<Widget> list, String item) {
                list.add(InkWell(
                  onTap: () {
                    onTap(items.indexOf(item));
                    Navigator.pop(context);
                  },
                  child: new Container(
                    height: 48.0,
                    alignment: AlignmentDirectional.center,
                    child: new Text(
                      item,
                      style: const TextStyle(
                        fontSize: 18.0,
                        color: CupertinoColors.activeBlue,
                      ),
                    ),
                  ),
                ));

                if (item != remaining.last) {
                  list.add(new Container(
                    height: 0.5,
                    color: Colors.grey,
                  ));
                }

                return list;
              }),
            ),
          ));

          return new Column(
            mainAxisSize: MainAxisSize.min,
            children: widgets.reversed.toList(),
          );
        },
      ),
    );
  }
}