ReorderableList crash when reversed

[BirjuVachhani]

Is there an existing issue for this?

• I have searched the existing issues
• I have read the guide to filing a bug

Steps to reproduce

ReorderableList or ReorderableListView.builder widget throws when reverse:true.

Steps to Reproduce:

1. Run the sample code.
2. Click/Tap on Item 5. This results into a crash on the console.
3. Drag Item 5 triggering a reorder and place it back at its original position. This also results into a crash.

This only happens when reverse is set to true on the widget. Note that onReorder or onReorderEnd never gets called in this case even if specified. (I don't know if onReorder should be called since nothing changed but onReorderEnd should be called which is the case for other items except the last one (first one since the list is reversed).

Expected results

No crash.

Actual results

======== Exception caught by gesture library =======================================================
The following _TypeError was thrown while routing a pointer event:
Null check operator used on a null value

When the exception was thrown, this was the stack: 
#0      SliverReorderableListState._itemOffsetAt (package:flutter/src/widgets/reorderable_list.dart:911:51)
#1      SliverReorderableListState._dragEnd.<anonymous closure> (package:flutter/src/widgets/reorderable_list.dart:760:30)
#2      State.setState (package:flutter/src/widgets/framework.dart:1139:30)
#3      SliverReorderableListState._dragEnd (package:flutter/src/widgets/reorderable_list.dart:758:5)
#4      _DragInfo.end (package:flutter/src/widgets/reorderable_list.dart:1281:12)
#5      MultiDragPointerState._up (package:flutter/src/gestures/multidrag.dart:156:14)
#6      MultiDragGestureRecognizer._handleEvent (package:flutter/src/gestures/multidrag.dart:258:13)
#7      PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:98:12)
#8      PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:143:9)
#9      _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:625:13)
#10     PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:141:18)
#11     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:127:7)
#12     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:465:19)
#13     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:445:22)
#14     RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:331:11)
#15     GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:400:7)
#16     GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:363:5)
#17     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:320:7)
#18     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:293:9)
#19     _invoke1 (dart:ui/hooks.dart:158:13)
#20     PlatformDispatcher._dispatchPointerDataPacket (dart:ui/platform_dispatcher.dart:382:7)
#21     _dispatchPointerDataPacket (dart:ui/hooks.dart:91:31)
====================================================================================================

Code sample

Code sample

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'MyApp Demo',
      debugShowCheckedModeBanner: false,
      home: MyHome(),
    );
  }
}

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

  @override
  State<MyHome> createState() => _MyHomeState();
}

class _MyHomeState extends State<MyHome> {
  final List<String> items = [
    'Item 1',
    'Item 2',
    'Item 3',
    'Item 4',
    'Item 5',
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ReorderableList(
        onReorder: (int oldIndex, int newIndex) {
          setState(
            () {
              // Taken from Flutter SDK code documentation.
              if (newIndex > oldIndex) {
                newIndex -= 1;
              }
              final String item = items.removeAt(oldIndex);
              items.insert(newIndex, item);
            },
          );
        },
        itemCount: items.length,
        reverse: true,
        itemBuilder: (BuildContext context, int index) {
          return ReorderableDragStartListener(
            key: Key('$index'),
            index: index,
            child: Material(
              child: ListTile(
                title: Text(items[index]),
              ),
            ),
          );
        },
      ),
    );
  }
}

Screenshots or Video

Screenshots / Video demonstration

Screen.Recording.2023-08-07.at.11.48.20.PM.mp4

Logs

Logs

Performing hot reload...
Syncing files to device macOS...
Reloaded 1 of 1013 libraries in 138ms (compile: 16 ms, reload: 53 ms, reassemble: 57 ms).

======== Exception caught by gesture library =======================================================
The following _TypeError was thrown while routing a pointer event:
Null check operator used on a null value

When the exception was thrown, this was the stack: 
#0      SliverReorderableListState._itemOffsetAt (package:flutter/src/widgets/reorderable_list.dart:911:51)
#1      SliverReorderableListState._dragEnd.<anonymous closure> (package:flutter/src/widgets/reorderable_list.dart:760:30)
#2      State.setState (package:flutter/src/widgets/framework.dart:1139:30)
#3      SliverReorderableListState._dragEnd (package:flutter/src/widgets/reorderable_list.dart:758:5)
#4      _DragInfo.end (package:flutter/src/widgets/reorderable_list.dart:1281:12)
#5      MultiDragPointerState._up (package:flutter/src/gestures/multidrag.dart:156:14)
#6      MultiDragGestureRecognizer._handleEvent (package:flutter/src/gestures/multidrag.dart:258:13)
#7      PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:98:12)
#8      PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:143:9)
#9      _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:625:13)
#10     PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:141:18)
#11     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:127:7)
#12     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:465:19)
#13     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:445:22)
#14     RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:331:11)
#15     GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:400:7)
#16     GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:363:5)
#17     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:320:7)
#18     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:293:9)
#19     _invoke1 (dart:ui/hooks.dart:158:13)
#20     PlatformDispatcher._dispatchPointerDataPacket (dart:ui/platform_dispatcher.dart:382:7)
#21     _dispatchPointerDataPacket (dart:ui/hooks.dart:91:31)
====================================================================================================

Flutter Doctor output

Doctor output

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[TahaTesser]

Hi @BirjuVachhani
Thanks for the report. This is regressed in #111027

[TahaTesser]

cc: @Hangyujin

[opxdelwin]

I found the issue. This happens when the dragged item (item 5) is the last element of _items list in files.

Pretty easy fix, add a conditional statement. I got this done locally, but I'm afraid, the reset animation is quite snappy. find this video.

Can open a PR as required, do suggest.

2023-08-08.16-09-52.mp4