Скачать или смотреть Fixing the Scaffold.of() Error When Showing Snack Bars in Flutter

Learn how to resolve the `Scaffold.of()` error in Flutter when attempting to show a SnackBar by using a GlobalKey for the Scaffold.
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This video is based on the question https://stackoverflow.com/q/64352153/ asked by the user 'Vincenzo' ( https://stackoverflow.com/u/9663497/ ) and on the answer https://stackoverflow.com/a/64352261/ provided by the user 'Omer Gamliel' ( https://stackoverflow.com/u/11000728/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing the Scaffold.of() Error When Showing Snack Bars in Flutter

If you're a Flutter developer, you may have encountered the frustrating Scaffold.of() called with a context that does not contain a Scaffold error. This often occurs when you're trying to display a SnackBar after an action, such as confirming a deletion, but the context from which you call Scaffold.of(context) does not have an associated Scaffold. In this guide, we'll identify the problem and provide clear steps to solve it effectively.

Understanding the Problem

In Flutter, the Scaffold widget is responsible for implementing the basic visual layout structure of an app. It contains components such as the AppBar, Drawer, BottomNavigationBar, and SnackBars. When you try to show a SnackBar, the context used must point to the specific Scaffold you're working with. If it doesn't, you'll encounter the aforementioned error.

This issue typically arises in scenarios where a dialog or other UI component is active and the context used for the SnackBar does not refer to the Scaffold currently displayed on the screen. This is a common situation when integrating state management solutions like BLoC, where you want to perform an action like showing a SnackBar based on the state of your application.

Solution: Using a GlobalKey for Scaffold

To resolve the Scaffold.of() error, we can make use of a GlobalKey to directly reference the Scaffold. This allows us to show a SnackBar without relying on the local context, which may not be correctly associated with a Scaffold. Here’s how to implement this solution:

Step 1: Create a GlobalKey

First, declare a GlobalKey<ScaffoldState> in your stateful widget. This will be used to reference the Scaffold across your widget tree.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Assign the Key to Your Scaffold

Next, assign this GlobalKey to the Scaffold widget within your build method.

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Show SnackBar Using the GlobalKey

Instead of using Scaffold.of(context).showSnackBar(...), use the scaffoldKey to show your SnackBar whenever necessary. For example, when a booking is deleted:

[[See Video to Reveal this Text or Code Snippet]]

Complete Example

Here is how your _BookingsScreenState class might look after implementing the solution:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By utilizing a GlobalKey for your Scaffold, you can effectively manage SnackBars and other UI elements without running into context-related errors. This approach not only simplifies your code but also improves the clarity and maintainability of your widget tree in Flutter. Next time you encounter the Scaffold.of() error, remember to switch to using GlobalKey. Happy coding!