Flutter: How to open Drawer programmatically

Null safe code

• 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.
        );
      }),
    );
  }
  

---

If you want to disable opening the Drawer using a drag gesture, you can set

Scaffold(
  drawerEnableOpenDragGesture: false
  // above code ...
)

1. To disable the slide to open functionality you can set the property drawerEnableOpenDragGesture on Scaffold to false.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        // this to prevent the default sliding behaviour
        drawerEnableOpenDragGesture: false,
        drawer: Drawer(),
        appBar: AppBar(
          leading: Builder(builder: (context) => // Ensure Scaffold is in context
            IconButton(
              icon: Icon(Icons.menu),
              onPressed: () => Scaffold.of(context).openDrawer()
            ),
          ),
        )
      )
    );
  }
}

2. To open the drawer programmatically using Scaffold.of(context) you'll have to ensure (thanks Krolaw !) that the context inside which the call is made is aware of the Scaffold.

   A clean way to do it is to wrap the button in a builder. I've edited the answer to include a minimal full working example.

   Scaffold is a widget that implements material design principles, so be aware that to be able to call this method, you'll need to import 'package:flutter/material.dart'; and your widget needs to have a MaterialApp as ancestor.

Codepen demo

---

As with many Flutter things, there are other solutions to ensure Scaffold is in context.

Error messages are IMO among the best features of flutter framework, allow me to humbly suggest to always read them thoroughly and to explore the documentation they point at.

For instance, this is part of the error message that one gets if calling openDrawer outside of a proper context:

Scaffold.of() called with a context that does not contain a Scaffold.

No Scaffold ancestor could be found starting from the context that was passed to Scaffold.of(). This usually happens when the context provided is from the same StatefulWidget as that whose build function actually creates the Scaffold widget being sought.

There are several ways to avoid this problem. The simplest is to use a Builder to get a context that is "under" the Scaffold. For an example of this, please see the documentation for Scaffold.of(): https://api.flutter.dev/flutter/material/Scaffold/of.html

A more efficient solution is to split your build function into several widgets. This introduces a new context from which you can obtain the Scaffold. In this solution, you would have an outer widget that creates the Scaffold populated by instances of your new inner widgets, and then in these inner widgets you would use Scaffold.of().

A less elegant but more expedient solution is assign a GlobalKey to the Scaffold, then use the key.currentState property to obtain the ScaffoldState rather than using the Scaffold.of() function.