final GlobalKey<ScaffoldState> _key = GlobalKey(); // Create a key


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _key,
      appBar: AppBar(),
      body: Container(
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              MaterialButton(onPressed: (){
                _key.currentState!.openDrawer();
              }, child: Text("Click me"),),
            ],
          ),
        ),
      ),
      drawer: Drawer(
        child: ListView(
          children: [
            DrawerHeader(
              decoration: BoxDecoration(color: Colors.blue),
              padding: EdgeInsets.all(10),
              child: Column(
                mainAxisAlignment: MainAxisAlignment.end,
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Container(
                    width: 70,
                    height: 70,
                    child: CircleAvatar(
                      backgroundImage: AssetImage('assets/img/background/image-5.png'),
                    ),
                  ),
                  SizedBox(
                    height: 10,
                  ),
                  Text('GeeCoders'),
                ],
              ),
            ),
            GestureDetector(
              onTap: (){
                print('clicked');
              },
              child: ListTile(
                leading: Icon(
                  Icons.home,
                  color: Colors.redAccent,
                ),
                title: Text('Home Page'),
              ),
            ),
            ListTile(
              leading: Icon(
                Icons.fiber_new,
                color: Colors.redAccent,
              ),
              title: Text('Second Page'),
            ),
            GestureDetector(
              onTap: (){
                Navigator.pop(context);
              },
              child: ListTile(
                leading: Icon(
                  Icons.accessibility,
                  color: Colors.redAccent,
                ),
                title: Text('Third Page'),
              ),
            ),
          ],
        ),
      ),
    );
  }