Скачать или смотреть How to Fix Can't Call Function Inside setState() Error in Flutter

Learn how to solve the issue of changing colors in Flutter when a button is pressed, by correctly managing state and moving variables outside of the build method.
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This video is based on the question https://stackoverflow.com/q/66563478/ asked by the user 'AndryCraft69' ( https://stackoverflow.com/u/13319856/ ) and on the answer https://stackoverflow.com/a/66563625/ provided by the user 'osaxma' ( https://stackoverflow.com/u/10976714/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Common Flutter Issue: Can't Call Function Inside setState()

As developers, we often run into small issues that make a big difference in our applications. One common problem that Flutter developers face is being unable to call functions inside setState(). In this guide, we will explore a real-world example that illustrates this issue and provide a clear and effective solution.

The Problem

Imagine you're working on a Flutter app that features a month calendar. You want users to tap a day in the calendar, changing its color to indicate selection, while also resetting the colors of other days back to the default. However, despite your best efforts, the color of the selected day simply doesn’t change.

Here's the crux of your problem: when you try to call the function changeColor() inside the setState(), nothing happens. This can be confusing, especially for beginners in Flutter.

The Current Code

Your original code looks something like this:

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

The Solution

To resolve this, you need to move the dateColor variable outside of the build method. By keeping it inside the build method, you essentially reset the value of dateColor every time the widget rebuilds. Here's how you can modify the code:

Revised Code

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

Key Changes Made

Moved dateColor Declaration: By declaring dateColor outside of the build method, we ensure its value persists between builds, allowing the UI to reflect the state change effectively.

Calling changeColor(): Now that the state has managed correctly, when you tap the button, it will successfully call changeColor() and update the color of the pressed Container.

Conclusion

Flutter development can sometimes feel overwhelming, especially when you're learning to manage state effectively. By understanding where to declare your variables and how setState() works, you can overcome many common pitfalls like the one illustrated here.

Now, when you press the button, the color of the selected Container will change from white to blue, and all other Containers will revert back to white as intended. Happy coding!