Flutter State Management: Accessing Scaffold State with GlobalKey
Published: 2023-08-02 09:52:00

In [Flutter](https://docs.flutter.dev/), a widget's **"scope"** refers to its enclosing widget tree and the context in which it is defined. While a widget can access properties and methods of its immediate parent and itself, accessing widgets higher up (**ancestors**) or lower down (**descendants**) in the tree can be challenging.

In certain scenarios, you may encounter situations where you need to interact with a widget outside your current scope. For instance, you might want a button in a child widget to trigger an action in its parent or activate a function in a deeply nested widget that affects a top-level widget.

For such cases, the `Scaffold` widget plays a pivotal role. It offers methods like `openDrawer()`, `showSnackBar()`, etc., which control its behavior and perform scaffold-related actions.

``` dart
import 'package:flutter/material.dart';

class MyWidget extends StatelessWidget {
  final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldKey,
      // ... rest of the widget ...
    );
  }
} 
```


## The Case
In a recent scenario, I utilized the `_scaffoldKey` to render a [`drawer`](https://docs.flutter.dev/cookbook/design/drawer). In Flutter's architecture, the Scaffold widget employs a `GlobalKey` to manage and control its state. The `GlobalKey<ScaffoldState>` is **indispensable** when you must access scaffold widget properties and methods beyond its immediate scope.

My specific case involved opening the `drawer` from a child widget, where the drawer resided at the **top level of the widget** tree—beyond the child's scope. To achieve this, I needed a way to access the `ScaffoldState` of the Scaffold widget.

### Here's a breakdown of the process:

- Upon defining a **Scaffold widget**, it generates a `ScaffoldState` object that encapsulates the current scaffold state.
- To access the scaffold's state, you need a reference to the `ScaffoldState` object. This is where the `GlobalKey<ScaffoldState>` proves invaluable.
- By defining a `GlobalKey<ScaffoldState>`, you can associate it with the Scaffold widget using the key property. This establishes a link to the `ScaffoldState` within the **Scaffold widget**.
- Upon tapping the menu icon (housed in a GestureDetector within the child widget), we invoke the `openDrawer()` method on the `ScaffoldState` obtained from `_scaffoldKey`. This action triggers the opening of the **drawer**.

```dart
GestureDetector(
  onTap: () {
    _scaffoldKey.currentState!.openDrawer();
  },
  child: Icon(Icons.menu),
)
```

## Conclusion
In conclusion, leveraging `_scaffoldKey` with `GlobalKey<ScaffoldState>` furnishes us with a mechanism to engage with the Scaffold widget and access its state from a child widget. This capability proves pivotal for executing actions such as drawer opening, snack bar presentation, bottom sheet display, and more—actions that mandate interaction with the Scaffold widget from the child widget's contextual domain.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/e7hwn2mph2hzdny2ovk7.PNG)

Remember, this technique empowers you to extend your widget's reach and enables seamless communication and interaction across different parts of your widget tree in Flutter.