README.md

linked_scroll_controller

This package provides a way to set up a set of scrollable widgets whose scrolling is synchronized. The set can be stable across the lifetime of the containing screen, or can change dynamically (for example, a vertically scrolling ListView.builder() whose items are Scrollables that scroll horizontally in unison).

If you add controllers dynamically, the corresponding scrollables must be given unique keys to avoid the scroll offset going out of sync.

Example usage

The code below sets up two side-by-side ListViews that scroll in unison.

class LinkedScrollables extends StatefulWidget {
  @override
  _LinkedScrollablesState createState() => _LinkedScrollablesState();
}

class _LinkedScrollablesState extends State<LinkedScrollables> {
  LinkedScrollControllerGroup _controllers;
  ScrollController _letters;
  ScrollController _numbers;

  @override
  void initState() {
    super.initState();
    _controllers = LinkedScrollControllerGroup();
    _letters = _controllers.addAndGet();
    _numbers = _controllers.addAndGet();
  }

  @override
  void dispose() {
    _letters.dispose();
    _numbers.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Directionality(
      textDirection: TextDirection.ltr,
      child: Row(
        children: [
          Expanded(
            child: ListView(
              controller: _letters,
              children: <Widget>[
                _Tile('Hello A'),
                _Tile('Hello B'),
                _Tile('Hello C'),
                _Tile('Hello D'),
                _Tile('Hello E'),
              ],
            ),
          ),
          Expanded(
            child: ListView(
              controller: _numbers,
              children: <Widget>[
                _Tile('Hello 1'),
                _Tile('Hello 2'),
                _Tile('Hello 3'),
                _Tile('Hello 4'),
                _Tile('Hello 5'),
              ],
            ),
          ),
        ],
      ),
    );
  }
}

class _Tile extends StatelessWidget {
  final String caption;

  _Tile(this.caption);

  @override
  Widget build(_) => Container(
        margin: const EdgeInsets.all(8.0),
        padding: const EdgeInsets.all(8.0),
        height: 250.0,
        child: Center(child: Text(caption)),
      );
}