Flutter simple drawer

main.dart

import 'dart:ui' as ui show window;

import 'package:flutter/material.dart' show Colors;
import 'package:flutter/widgets.dart';

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

class App extends StatelessWidget {
  const App({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MediaQuery(
      child: DecoratedBox(
        child: Directionality(
          child: DefaultTextStyle(
            child: HomePage(),
            style: TextStyle(
              color: Colors.black,
              fontFamily: 'monospace',
              fontSize: 16.0,
            ),
          ),
          textDirection: TextDirection.ltr,
        ),
        decoration: BoxDecoration(
          color: Colors.white,
        ),
      ),
      data: MediaQueryData.fromWindow(ui.window),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  HomePageState createState() {
    return HomePageState();
  }
}

class HomePageState extends State<HomePage> with SingleTickerProviderStateMixin {
  bool showUserDrawer;
  AnimationController userDrawerController;
  Animation<double> userDrawerAnimation;

  void _update() {
    setState(() {});
  }

  void _hide(AnimationStatus status) {
    if (status == AnimationStatus.dismissed) {
      setState(() {
        showUserDrawer = false;
      });

      userDrawerController.removeStatusListener(_hide);
    }
  }

  @override
  void initState() {
    super.initState();
    showUserDrawer = false;
    userDrawerController = AnimationController(duration: Duration(milliseconds: 250), vsync: this);
    userDrawerAnimation = CurvedAnimation(curve: Curves.easeInOut, parent: userDrawerController);
    userDrawerAnimation = Tween<double>(begin: 0.0, end: 1.0).animate(userDrawerAnimation);
    userDrawerController.addListener(_update);
  }

  @override
  void dispose() {
    super.dispose();
    userDrawerController.removeListener(_update);
    userDrawerController.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: <Widget>[
        GestureDetector(
          behavior: HitTestBehavior.opaque,
          child: Align(
            child: Text(widget.title ?? 'Hello World!'),
          ),
          onTap: () {
            setState(() {
              showUserDrawer = true;
            });

            userDrawerController.forward();
          },
        ),
        if (showUserDrawer)
          Row(
            children: <Widget>[
              Expanded(
                child: GestureDetector(
                  child: DecoratedBox(
                    decoration: BoxDecoration(
                      color: Colors.black.withOpacity(0.12 * userDrawerAnimation.value),
                    ),
                  ),
                  onTap: () {
                    if (showUserDrawer) {
                      userDrawerController.addStatusListener(_hide);
                      userDrawerController.reverse();
                    }
                  },
                ),
              ),
              SizedBox(
                child: UnconstrainedBox(
                  alignment: Alignment.centerLeft,
                  child: SizedBox(
                    child: DecoratedBox(
                      child: Align(
                        child: Text('hey ' * 5),
                      ),
                      decoration: BoxDecoration(
                        color: Colors.white,
                        boxShadow: <BoxShadow>[
                          BoxShadow(
                            blurRadius: 16.0 * 0.3,
                            color: Colors.black12,
                          ),
                        ],
                      ),
                    ),
                    width: 16.0 * 20.0,
                  ),
                  clipBehavior: Clip.antiAlias,
                  constrainedAxis: Axis.vertical,
                ),
                width: 16.0 * 20.0 * userDrawerAnimation.value,
              ),
            ],
            crossAxisAlignment: CrossAxisAlignment.stretch,
          ),
      ],
    );
  }
}