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Learn how to keep scrollbars visible in flutter nested SingleChildScrollViews for a better user experience in your web applications.
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This video is based on the question https://stackoverflow.com/q/76739529/ asked by the user 'David Escariz' ( https://stackoverflow.com/u/14789036/ ) and on the answer https://stackoverflow.com/a/76739756/ provided by the user 'offworldwelcome' ( https://stackoverflow.com/u/11760076/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Always Show Scrollbars in Flutter Nested ScrollViews

When developing web applications using Flutter, you may encounter situations where your widgets are wider or taller than the visible screen. A common scenario arises when working with a table that has a substantial amount of data. This can lead to issues when attempting to implement scrollbars in nested SingleChildScrollView widgets.

The Problem

In your Flutter application, you may be using nested SingleChildScrollView widgets to create a scrollable area for both horizontal and vertical content. However, the default behavior of the Scrollbar widget can be frustrating. By default, the scrollbar thumb only appears when the user reaches the end of the scrollable area. This can make navigation feel clunky, especially when users need to scroll through large datasets.

The Original Code

You likely have a code similar to the following:

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

In this setup, the vertical Scrollbar isn't consistently shown, which can hinder the user experience. So how can you ensure that both scrollbars are visible at all times?

Solution Explained

The key to resolving this issue lies in modifying the default notificationPredicate of the Scrollbar. By default, it only checks for scroll notifications with a depth == 0, which only applies to the outer Scrollbar. To make the nested scrollbar also visible when needed, you'll need to accommodate for when the notification's depth is greater than zero.

Step-by-step Solution

Override the notificationPredicate: You need to customize your Scrollbar widget to account for both depths. Implement a custom notification predicate that checks if the depth is greater than or equal to zero.

Adjust Your Code: Update your Scrollbar implementation as follows:

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

Key Changes

notificationPredicate: This modification makes sure that the scrolling logic takes into account any depth greater than or equal to zero. As a result, the scrollbar will always be displayed for both horizontal and vertical scrolling.

Conclusion

By implementing these changes, both of your nested scrollbars will remain visible regardless of whether the user has scrolled to the end of your widgets. This enhancement significantly improves the user experience by providing better control and visibility over lengthy content.

For anyone dealing with similar scroll issues in Flutter web applications, feel free to adopt this approach to ensure a seamless user interaction. Happy coding!