together_mobile/lib/use_reorderable_sliver.dart

import 'package:flutter/material.dart';
import 'package:reorderables/reorderables.dart';

void main() => runApp(MaterialApp(
      title: 'Reorderable Sliver List Demo',
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Reorderable Sliver List Demo'),
        ),
        body: const SliverExample(),
      ),
    ));

class SliverExample extends StatefulWidget {
  const SliverExample({super.key});

  @override
  _SliverExampleState createState() => _SliverExampleState();
}

class _SliverExampleState extends State<SliverExample> {
  late List<Widget> _rows;

  @override
  void initState() {
    super.initState();
    _rows = List<Widget>.generate(
      50,
      (int index) => SizedBox(
        width: double.infinity,
        child: Align(
          alignment: Alignment.centerLeft,
          child: Text('This is sliver child $index', textScaleFactor: 2),
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    void onReorder(int oldIndex, int newIndex) {
      setState(() {
        Widget row = _rows.removeAt(oldIndex);
        _rows.insert(newIndex, row);
      });
    }

    // Make sure there is a scroll controller attached to the scroll view that contains ReorderableSliverList.
    // Otherwise an error will be thrown.
    ScrollController scrollController =
        PrimaryScrollController.maybeOf(context) ?? ScrollController();

    return CustomScrollView(
      // A ScrollController must be included in CustomScrollView, otherwise
      // ReorderableSliverList wouldn't work
      controller: scrollController,
      slivers: <Widget>[
        SliverAppBar(
          expandedHeight: 210.0,
          flexibleSpace: FlexibleSpaceBar(
            title: const Text('ReorderableSliverList'),
            background: Image.network(
                'https://upload.wikimedia.org/wikipedia/commons/thumb/6/68/Yushan'
                '_main_east_peak%2BHuang_Chung_Yu%E9%BB%83%E4%B8%AD%E4%BD%91%2B'
                '9030.png/640px-Yushan_main_east_peak%2BHuang_Chung_Yu%E9%BB%83'
                '%E4%B8%AD%E4%BD%91%2B9030.png'),
          ),
        ),
        ReorderableSliverList(
          delegate: ReorderableSliverChildListDelegate(_rows),
          // or use ReorderableSliverChildBuilderDelegate if needed
//          delegate: ReorderableSliverChildBuilderDelegate(
//            (BuildContext context, int index) => _rows[index],
//            childCount: _rows.length
//          ),
          onReorder: onReorder,
          onNoReorder: (int index) {
            //this callback is optional
            debugPrint(
              '${DateTime.now().toString().substring(5, 22)} reorder cancelled. index:$index',
            );
          },
          onReorderStarted: (int index) {
            debugPrint(
              '${DateTime.now().toString().substring(5, 22)} reorder started. index:$index',
            );
          },
        )
      ],
    );
  }
}