Added optional param for scrollController

[jcsena]

Dear code reviewers,

I am submitting this pull request to add a scroll controller to our trimmer listview widget in Flutter.

The scroll controller is an essential aspect of any scrolling widget, as it allows us to control the position and movement of the listview. In particular, for a trimmer listview, having a scroll controller is crucial to implement features such as adjusting the visible items, or moving to a specific item in the list based on user input.

The scroll controller provides several parameters that can be used to customize the scrolling behavior of the listview, such as:

initialScrollOffset: sets the initial scroll offset when the listview is first displayed.
keepScrollOffset: determines whether the scroll offset is preserved when the widget is rebuilt.
debugLabel: sets a label for the scroll controller, useful for debugging purposes.
By adding a scroll controller to our trimmer listview, we can ensure that the scrolling behavior is consistent, smooth, and easily adjustable. It also enables us to add new functionality that requires a precise control over the scrolling.

Additionally, I would like to bring to your attention that when using the updateTrim(x, 1.0) method, the scroll position may not be modified as expected. To overcome this issue, we need to manually update the scroll position using the jumpTo or animateTo methods provided by the scrollController.

Here's an example of how to use these methods to ensure that the scroll position is updated correctly:

  // Updating the new trim params manual to the end
 _controller.updateTrim(_start, 1.0)

  // Calculate the new scroll offset based on the updated trim value
  double newScrollOffset = ...;
  
  // Animate the scroll position to the new offset
  _scrollController.animateTo(newScrollOffset, duration: Duration(milliseconds: 500), curve: Curves.easeInOut);

I hope you will find this change useful and I look forward to your feedback.

Best regards,

[LeGoffMael]

Thank you for your work, i will be happy to accept your PR!
I will check the scroll position issue when using updateTrim() separately

[jcsena]

That sounds great!! And better idea!! thanks for your quickly feedback.

[LeGoffMael]

Should be now working in scroll-controller branch, i will test it more tomorrow as well before releasing it

[LeGoffMael]

sorry for the delay, your feature is available in the latest 2.4.0