AnimationController.stop() called after dispose in _moveToNextViewWithAnimation when calendar widget is torn down during gesture

[ttsakalos]

Bug description

Package: syncfusion_flutter_calendar
Version: 31.1.19
Flutter: stable

Description

When an SfCalendar is disposed mid-gesture (e.g. the user taps the forward/backward navigation arrow at the exact moment a tab switch tears down the widget tree), an assertion fires in debug mode:

AnimationController.stop() called after AnimationController.dispose()
Failed assertion: line 897 pos 7: '_ticker != null'

Stack trace

#2  AnimationController.stop (animation_controller.dart:897)
#3  AnimationController.value= (animation_controller.dart:373)
#4  AnimationController.reset (animation_controller.dart:394)
#5  _CustomCalendarScrollViewState._moveToNextViewWithAnimation (calendar_view.dart:3378)

Root cause

_moveToNextViewWithAnimation calls _animationController.reset() without first checking mounted.

If the State is disposed (e.g. due to a concurrent widget rebuild), the AnimationController has already been disposed and the call throws.

Suggested fix

Add a mounted guard in _moveToNextViewWithAnimation before operating on _animationController:

void _moveToNextViewWithAnimation() {
  if (!mounted) return;

  _animationController.reset();
  ...
}

Severity

Debug-only assertion (release builds are unaffected), but it causes repeated red-screen errors during development.

Steps to reproduce

1. Implement an SfCalendar within a view that can be quickly navigated away from (e.g., inside a TabBarView or a GoRouter page).
2. Add a custom header with buttons that call calendarController.forward() or calendarController.backward().
3. Tap the navigation button (Forward/Backward) and immediately trigger a navigation/tab switch that disposes of the calendar widget (e.g., tap the arrow and then a different tab icon in rapid succession).
4. The internal AnimationController attempt to reset() or stop() during the tear-down process, triggering the assertion.

Code sample

import 'package:flutter/material.dart';
import 'package:syncfusion_flutter_calendar/calendar.dart';

void main() => runApp(const MaterialApp(home: ReproPage()));

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

@OverRide
State createState() => _ReproPageState();
}

class _ReproPageState extends State {
final CalendarController _controller = CalendarController();
bool _showCalendar = true;

@OverRide
Widget build(BuildContext context) {
return Scaffold(
body: Column(
children: [
if (_showCalendar)
Expanded(
child: SfCalendar(
controller: _controller,
view: CalendarView.month,
),
),
ElevatedButton(
onPressed: () {
// Trigger navigation and immediate disposal
_controller.forward!();
setState(() => _showCalendar = false);
},
child: const Text('Navigate Forward & Dispose'),
),
],
),
);
}
}

Screenshots or Video

Not applicable.

Stack Traces

════════ Exception caught by gesture ═══════════════════════════════════════════
The following assertion was thrown while handling a gesture:
AnimationController.stop() called after AnimationController.dispose()
AnimationController methods should not be used after calling dispose.
'package:flutter/src/animation/animation_controller.dart':
Failed assertion: line 897 pos 7: '_ticker != null'

When the exception was thrown, this was the stack:
#2 AnimationController.stop (package:flutter/src/animation/animation_controller.dart:897:7)
#3 AnimationController.value= (package:flutter/src/animation/animation_controller.dart:373:5)
#4 AnimationController.reset (package:flutter/src/animation/animation_controller.dart:394:5)
#5 _CustomCalendarScrollViewState._moveToNextViewWithAnimation (package:syncfusion_flutter_calendar/src/calendar/views/calendar_view.dart:3378:28)
#6 _CalendarCustomHeaderState._goToAdjacentPeriod (package:worklife/application/calendar/components/calendar_custom_header/calendar_custom_header.dart:49:35)
...
Handler: "onTap"
Recognizer: TapGestureRecognizer#8acee

On which target platforms have you observed this bug?

Android

Flutter Doctor output

[√] Flutter (Channel stable, 3.38.7, on Microsoft Windows [Version 10.0.26200.8246])
• Flutter version 3.38.7 on channel stable
• Framework revision 3b62efc2a3 (2026-01-13)
• Dart version 3.10.7
• DevTools version 2.51.1

[√] Android toolchain - develop for Android devices (Android SDK version 36.1.0)
• Java version OpenJDK Runtime Environment (build 21.0.7+-13880790-b1038.58)

[√] Connected device (4 available)
• sdk gphone64 x86 64 (mobile) • emulator-5554 • android-x64 • Android 16 (API 36)

[Mugunthan-Ramalingam]

Hi Thodoris,

We have replicated the reported issue regarding the AnimationController disposal when navigating and disposing the SfCalendar widget simultaneously. The issue is scheduled to be fixed in our upcoming weekly patch release on May 26, 2026. We will notify you here once the release has been rolled out, and we appreciate your patience in the meantime.

Root cause:
The animation controller executes pending frame callbacks after the calendar widget is disposed, causing the animation reset/stop operations to fail on an already-destroyed animation controller. This occurs when navigation and widget disposal happen in quick succession, creating a race condition between animation callbacks and widget teardown.

Regards,
Mugunthan.

[Mugunthan-Ramalingam]

Hi Thodoris,

We have fixed the reported issue related to the AnimationController disposal when navigating away from the SfCalendar widget. However, we have encountered compatibility issues with our calendar widget following the latest Flutter version 3.44 release, which prevented us from including this fix in the planned weekly release.

We are currently addressing these compatibility changes and will include the fix in our next weekly patch release scheduled for June 02, 2026.

We sincerely apologize for the delay and any inconvenience this may have caused. Thank you for your understanding and patience.

Regards,
Mugunthan.

[Mugunthan-Ramalingam]

Hi Thodoris,

The reported issue has been resolved, and the fix is included in the version mentioned below. We kindly request you to upgrade the syncfusion_flutter_calendar package to the latest version to avoid this issue.

Version: https://pub.dev/packages/syncfusion_flutter_calendar/versions/33.2.10

Root Cause:
The animation controller executes pending frame callbacks after the calendar widget is disposed, causing the animation reset/stop operations to fail on an already-destroyed animation controller. This occurs when navigation and widget disposal happen in quick succession, creating a race condition between animation callbacks and widget teardown.

Regards,
Mugunthan.