How To Onclick Button Open Drawer Using Flutter Android

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.pink,
      ),
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  var _scaffoldKey = new GlobalKey<ScaffoldState>();
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      key: _scaffoldKey,
      endDrawer: new AppDrawer(),
      appBar: new AppBar(
        title: new Text("Onclick Button Open Drawer"),
      ),
      body: new ListView(
        children: <Widget>[
          Padding(
            padding: const EdgeInsets.only(top:40.0),
            child: new ListTile(
              title: new RaisedButton(
                textColor: Colors.white,
                color: Colors.pink[800],
                child: new Text("Open Drawer"),
                onPressed: () {
                  _scaffoldKey.currentState.openDrawer();
                  _scaffoldKey.currentState.openEndDrawer();
                },
              ),
            ),
          ),
        ],
      ),
    );
  }
}


class AppDrawer extends StatefulWidget {
  @override
  _AppDrawerState createState() => new _AppDrawerState();
}

class _AppDrawerState extends State<AppDrawer> {
  @override
  Widget build(BuildContext context) {
    return Container(
      width: 250,
      child: new Drawer(
        child: Container(
          color: Colors.pink[800],
          child: ListView(
            padding: EdgeInsets.all(10.0),
            children: [
              ListTile(
                leading: Icon(Icons.home, color: Colors.white,),
                title: Text('Home',style: TextStyle(color: Colors.white),),
              ),
              ListTile(
                leading: Icon(Icons.person, color: Colors.white,),
                title: Text('Profile',style: TextStyle(color: Colors.white),),
              ),
              ListTile(
                leading: Icon(Icons.phone, color: Colors.white,),
                title: Text('Contact',style: TextStyle(color: Colors.white),),
              ),
              ListTile(
                leading: Icon(Icons.settings, color: Colors.white,),
                title: Text('Setting',style: TextStyle(color: Colors.white),),
              ),
              ListTile(
                leading: Icon(Icons.help_outline, color: Colors.white,),
                title: Text('Help',style: TextStyle(color: Colors.white),),
              ),
            ],
          ),
        ),
      ),
    );
  }
}