Flutter Sortable Drag And Drop ListView

Question

So I'm starting to learn Flutter and would like to use a material design drag and drop list just like the one seen on the material guidelines website.

https://storage.googleapis.com/spec-host-backup/mio-design%2Fassets%2F1dtprsH4jZ2nOnjBCJeJXd7n4U-jmWyas%2F03-list-reorder.mp4

All of the libraries I have tried out so far look like garbage compared to that. Is there a good library for this that I am missing or a native Flutter widget?

Answer 1

You can use native flutter widget, ReorderableListView to achieve it, here is the example of doing it.

List<String> _list = ["Apple", "Ball", "Cat", "Dog", "Elephant"];

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(),
    body: ReorderableListView(
      children: _list.map((item) => ListTile(key: Key("${item}"), title: Text("${item}"), trailing: Icon(Icons.menu),)).toList(),
      onReorder: (int start, int current) {
        // dragging from top to bottom
        if (start < current) {
          int end = current - 1;
          String startItem = _list[start];
          int i = 0;
          int local = start;
          do {
            _list[local] = _list[++local];
            i++;
          } while (i < end - start);
          _list[end] = startItem;
        }
        // dragging from bottom to top
        else if (start > current) {
          String startItem = _list[start];
          for (int i = start; i > current; i--) {
            _list[i] = _list[i - 1];
          }
          _list[current] = startItem;
        }
        setState(() {});
      },
    ),
  );
}

Answer 2

Flutter itself provides a (Material) ReorderableListView class.

Answer 3

I've tried flutter_reorderable_list and dragable_flutter_list but none of them worked properly - there was some unwanted artifacts during dragging. So I've tried to make own solution:

ListView.builder(
  itemBuilder: (context, index) => buildRow(index),
  itemCount: trackList.length,
),

Widget buildRow(int index) {
  final track = trackList[index];
  ListTile tile = ListTile(
    title: Text('${track.getName()}'),
  );
  Draggable draggable = LongPressDraggable<Track>(
    data: track,
    axis: Axis.vertical,
    maxSimultaneousDrags: 1,
    child: tile,
    childWhenDragging: Opacity(
      opacity: 0.5,
      child: tile,
    ),
    feedback: Material(
      child: ConstrainedBox(
        constraints:
            BoxConstraints(maxWidth: MediaQuery.of(context).size.width),
        child: tile,
      ),
      elevation: 4.0,
    ),
  );

  return DragTarget<Track>(
    onWillAccept: (track) {
      return trackList.indexOf(track) != index;
    },
    onAccept: (track) {
      setState(() {
        int currentIndex = trackList.indexOf(track);
        trackList.remove(track);
        trackList.insert(currentIndex > index ? index : index - 1, track);
      });
    },
    builder: (BuildContext context, List<Track> candidateData,
        List<dynamic> rejectedData) {
      return Column(
        children: <Widget>[
          AnimatedSize(
            duration: Duration(milliseconds: 100),
            vsync: this,
            child: candidateData.isEmpty
                ? Container()
                : Opacity(
                    opacity: 0.0,
                    child: tile,
                  ),
          ),
          Card(
            child: candidateData.isEmpty ? draggable : tile,
          )
        ],
      );
    },
  );
}

I guess, this is not the best solution, and I'm maybe will change it further, but for now it works quite well