Resolving the Flutter Error: _positions.isNotEmpty: How to Properly Attach a ScrollController

Описание: Learn how to fix the Flutter error '_positions.isNotEmpty': ScrollController not attached to any scroll views by properly configuring your ListView with a ScrollController.
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This video is based on the question https://stackoverflow.com/q/76221853/ asked by the user 'muntazir halim' ( https://stackoverflow.com/u/18307259/ ) and on the answer https://stackoverflow.com/a/76222415/ provided by the user 'anuj-t21' ( https://stackoverflow.com/u/20916895/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Flutter Error: _positions.isNotEmpty

When working with Flutter, you might encounter rendering issues, especially when dealing with lists and scrollable views. One common error developers face is _positions.isNotEmpty': ScrollController not attached to any scroll views. This can be frustrating, particularly if you're unsure of what has gone wrong. In this post, we'll explain the cause of this issue and provide a simple, effective solution.

What Causes the Error?

The error essentially indicates that you are trying to use a ScrollController that hasn't been attached to any scrollable widget. In your case, it appears when you attempt to display a ListView without properly configuring the ScrollController.

The snippet of code provided gives us an insight into the issue:

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Here, the ListView.builder has not been assigned a ScrollController. This is the reason for your error message — without the controller property, the ListView does not know how to manage the scrolling behavior, leading to the error.

How to Fix the Error

Step 1: Declare a ScrollController

Before you can attach the ScrollController, you need to declare it within your stateful widget. This will allow you to manage the scroll position of your ListView effectively.

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Step 2: Attach the ScrollController to the ListView

Now that you have a ScrollController, you can utilize it within your ListView.builder. Just add the controller property when you create the ListView:

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Final Code Example

Your updated code should look something like this:

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Step 3: Dispose of the Controller

It is also important to dispose of the controller when the widget is removed from the widget tree to prevent memory leaks. You can do this in the dispose method:

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Conclusion

By properly attaching a ScrollController to your ListView, you can resolve the _positions.isNotEmpty error and ensure smooth scrolling behavior in your Flutter applications. Remember, the key takeaway is to link your ScrollController with the scrollable widget to prevent such errors.

If you have any more questions or need further clarification on Flutter development, feel free to reach out or leave a comment below! Happy coding!