Open drawer on clicking AppBar

Solution 1:

Use a Key in your Scaffold and show the drawer by calling myKey.currentState.openDrawer(), here is a working code:

import "package:flutter/material.dart";

class Test extends StatefulWidget {
  @override
  _TestState createState() => new _TestState();
}

class _TestState extends State<Test> {
  final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      key: _scaffoldKey,
      drawer: new Drawer(),
      appBar: new AppBar(
        leading: new IconButton(
          icon: new Icon(Icons.settings),
          onPressed: () => _scaffoldKey.currentState.openDrawer(),
        ),
      ),
    );
  }
}

Solution 2:

Alternative to the accepted answer which does not require a GlobalKey:

class _TestState extends State<Test> {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      drawer: new Drawer(),
      appBar: new AppBar(
        leading: Builder(
        builder: (context) => IconButton(
            icon: new Icon(Icons.settings),
            onPressed: () => Scaffold.of(context).openDrawer(),
          ),
        ),
      ),
    );
  }
}

Solution 3:

you need initialize scaffoldKey after that,

Open drawer and close drawer

 GestureDetector(
          onTap: () {
            if(scaffoldKey.currentState.isDrawerOpen){
              scaffoldKey.currentState.openEndDrawer();
            }else{
              scaffoldKey.currentState.openDrawer();
            }
          },
          child:  LeadingIcon(icon: Icons.menu),//your button
        ),

Solution 4:

Using GlobalKey:

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

@override
Widget build(BuildContext context) {
  return Scaffold(
    key: _key, // Assign the key to Scaffold.
    drawer: Drawer(),
    floatingActionButton: FloatingActionButton(
      onPressed: () => _key.currentState!.openDrawer(), // <-- Opens drawer
    ),
  );
}

Using Builder:

@override
Widget build(BuildContext context) {
  return Scaffold(
    drawer: Drawer(),
    floatingActionButton: Builder(builder: (context) {
      return FloatingActionButton(
        onPressed: () => Scaffold.of(context).openDrawer(), // <-- Opens drawer.
      );
    }),
  );
}