My expectation from ReoderableListView.builder() is simply, as what the Flutter doc says, to create a widget that allows users to move/drag list-items up and down the list view. However, what I was getting from my emulator was no dragging animation, no reordering of the list (upon user input), and not even call to the onReorder callback.

Stuff I have tried:

1. Made sure my taskID and taskName lists have the same length
2. Added debug outputs for itemBuilder and onReorder callback, surprisingly receiving debug output only from itemBuilder callback
3. Copied and pasted the widget code and its corresponding lists data exactly to other widget classes (or files) and still got the same result
4. Added the exactly same ValueKey in the Text() inside the list-view.
5. Tried using the same list data as what the Text() is rendering, taskNames, for the value ValueKey

The only thing I did not try was directly copying and pasting the official example of this widget to my codebase, but the test code I have should already be very similar to the official example, structurally.

checklist.dart

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

import 'add_task.dart';

class Checklist extends StatefulWidget {
  const Checklist({Key? key}) : super(key: key);

  @override
  State<Checklist> createState() => _ChecklistState();
}

class _ChecklistState extends State<Checklist> {
  final List<int> taskID = <int>[0, 1, 2, 4, 6];
  final List<String> taskNames = <String>['A', 'B', 'C', 'D', 'E'];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Row(
          children: [
            const Text("TODO"),
            ElevatedButton(
              onPressed: () {

              },
              child: const Text("Google Calendar"),
              style: ButtonStyle(
                backgroundColor: MaterialStateProperty.all(Colors.black12),
              ),
            ),
          ]
        ),
      ),
      body: ReorderableListView.builder(
        itemCount: taskNames.length,
        itemBuilder: (BuildContext context, int index) {
          print("B");
          return ListTile(
            key: ValueKey(taskID[index]),
            tileColor: Colors.black12,
            title: Text('Entry ${taskNames[index]}')
          );
        },
        onReorder: (int oldIndex, int newIndex) {
          print("A");
          setState(() {
            if (newIndex > oldIndex) {
              newIndex -= 1;
            }
            final int elTid = taskID.removeAt(oldIndex);
            final String elTnm = taskNames.removeAt(oldIndex);
            taskID.insert(newIndex, elTid);
            taskNames.insert(newIndex, elTnm);
          });
        },
      ),
    );
  }
}

CodePudding user response：

Your code does work. It moves only on long press and drag. Not on normal drag.. On normal drag it will tend to scroll the list