Скачать или смотреть Solving the onPressed Callback Issue in Flutter's IconButton

Discover how to prevent the automatic execution of your onPressed method in a Flutter IconButton during widget initialization.
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This video is based on the question https://stackoverflow.com/q/69676771/ asked by the user '12pm' ( https://stackoverflow.com/u/1103436/ ) and on the answer https://stackoverflow.com/a/69680271/ provided by the user '12pm' ( https://stackoverflow.com/u/1103436/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
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Introduction

Flutter developers often encounter unexpected behaviors when working with widget callbacks. One common issue is the automatic invocation of a method assigned to an IconButton's onPressed property. If you've faced a situation where your onPressed method is getting called immediately upon widget initialization, you’re not alone. In this guide, we will explore this problem and provide a clear solution to prevent that unwanted behavior.

The Problem Explained

In the example provided, the goal is to show an overlapping widget using a stack when a button is pressed. Here's a simplified version of the code:

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

The error encountered is due to how the onPressed callback is defined in the MyFloatingWidget class:

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

In this snippet, widget.onClose() is being called immediately during the widget’s build phase, leading to the error: FlutterError (setState() or markNeedsBuild() called during build...).

Understanding the Solution

To resolve this issue, you need to ensure that you’re not invoking the function directly. Instead, you should pass a callback function that can be executed when the button is pressed. Here’s how you do it:

Step-by-Step Fix

Modify the onPressed Callback: Rather than calling the onClose method directly in the callback, wrap it in an anonymous function.

Replace the onPressed Code: Update the onPressed line in IconButton:

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

Updated Code

The corrected MyFloatingWidget class would look like this:

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

How It Works

Wrapping the widget.onClose() method in an anonymous function delays its execution until the IconButton is actually pressed. This way, the method will only run when you want it to, preventing the automatic call during the build phase.

Conclusion

The automatic execution of a method assigned to onPressed in Flutter’s IconButton can be a frustrating issue to troubleshoot. By following the adjustment outlined in this guide, you can easily resolve this problem. Always remember the importance of wrapping method calls in a function to ensure they are executed only when intended. Happy coding!