Custom AppBar for flutter

app_bar.dart

import 'package:flutter/material.dart';

// TODO: Continue investigating how to do scroll offset animation like this:
// https://dribbble.com/shots/2201752-Profile-Header-Interaction-Prototype

class CustomAppBar extends StatefulWidget {
  final String title;

  CustomAppBar({this.title});

  @override
  State<CustomAppBar> createState() {
    return new CustomAppBarState(title: title);
  }
}

class CustomAppBarState extends State<CustomAppBar> {
  final String title;
  final double barHeight = 66.0;

  CustomAppBarState({
    this.title
  });

  @override
  Widget build(BuildContext context) {
    final double statusBarHeight = MediaQuery.of(context).padding.top;
    final TextStyle titleStyle = const TextStyle(
      color: Colors.white,
      fontWeight: FontWeight.w400,
      fontSize: 22.0,
    );

    final ScaffoldState scaffold = Scaffold.of(context, nullOk: true);

    final bool canPop = ModalRoute.of(context).canPop;
    final bool hasDrawer = scaffold?.hasDrawer ?? false;
    final bool hasEndDrawer = scaffold?.hasEndDrawer ?? false;

    final List<Color> gradientColors = [
      const Color(0xFF7649F6),
      const Color(0xFFFC537F)
    ];

    final Widget backButton = new IconButton(
      icon: new Icon(Icons.arrow_back, size: 30.0, color: Colors.white),
      onPressed: () { 
        Navigator.of(context).pop();
      }
    );
    
    Widget _leading;
    Widget _ending;

    if (hasDrawer) {
      _leading = new IconButton(
        icon: new Icon(Icons.menu, size: 30.0, color: Colors.white),
        onPressed: () {
          Scaffold.of(context).openDrawer();
        }
      );
    } else {
      if (canPop) {
        _leading = backButton;
      } else {
        _leading = null;
      }
    }

    if (hasEndDrawer) {
      _ending = new IconButton(
        icon: new Icon(Icons.forum, size: 30.0, color: Colors.white),
        onPressed: () {
          Scaffold.of(context).openEndDrawer();
        }
      );
    } else {
      _ending = null;
    }

    return new Container(
      padding: new EdgeInsets.only(top: statusBarHeight),
      height: statusBarHeight + barHeight,
      decoration: new BoxDecoration(
        gradient: new LinearGradient(
          colors: gradientColors,
          begin: const FractionalOffset(0.0, 0.0),
          end: const FractionalOffset(0.9, 0.0),
          stops: [0.0, 0.9],
          tileMode: TileMode.clamp
        )
      ),
      child: new Stack(
        fit: StackFit.expand,
        children: <Widget>[
          new Align(
            alignment: Alignment.centerLeft,
            child: new Padding(
              padding: const EdgeInsets.only(left: 20.0),
              child: _leading
            )
          ),
          new Center(child: new Text(title, style: titleStyle)),
          new Align(
            alignment: Alignment.centerRight,
            child: new Padding(
              padding: const EdgeInsets.only(right: 16.0),
              child: _ending
            )
          ),
        ],
      )
    );
  }
}