[syncfusion_flutter_calendar] Appointment drag-and-drop snaps to incorrect start time when view is non-scrollable (timeIntervalHeight: -1)

[WieFel]

Bug description

When the SfCalendar is configured with a non-scrollable time-slot view (e.g., using timeIntervalHeight: -1 to auto-fit the screen or using a small manual height), dragging an appointment to a late hour causes the start time to "snap" back to an earlier time.

For example, dragging a 3-hour appointment to start at 22:00 (which would end at 01:00 the next day) results in the appointment being forced to start at 21:00 (or a jittery time like 21:05 depending on resolution) so that it ends exactly at 24:00.

Steps to reproduce

1. Initialize SfCalendar with view: CalendarView.day (or week/workWeek).
2. Set timeSlotViewSettings: const TimeSlotViewSettings(timeIntervalHeight: -1).
3. Create an appointment with a duration of 3 hours.
4. Enable drag-and-drop (allowDragAndDrop: true).
5. Attempt to drag the appointment to start at 10:00 PM (22:00).
6. Observe that the calendar prevents the move to 22:00 and instead forces the appointment to an earlier start time to ensure it doesn't "overflow" the visible day area.

Code sample

Code sample

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

void main() {
  return runApp(
    const MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(body: SafeArea(child: CalendarDragDrop())),
    ),
  );
}

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

  @override
  Widget build(BuildContext context) {
    return SfCalendar(
      view: CalendarView.week,
      allowDragAndDrop: true,
      timeSlotViewSettings: const TimeSlotViewSettings(timeIntervalHeight: -1),
      dataSource: _AppointmentDataSource(_getDataSource()),
      appointmentBuilder: (context, details) {
        final Appointment appointment = details.appointments.first;

        return Container(
          decoration: BoxDecoration(
            color: appointment.color,
            borderRadius: BorderRadius.circular(4),
          ),
          padding: const EdgeInsets.all(4),
          child: Text(
            '${appointment.subject}\n'
            '${TimeOfDay.fromDateTime(appointment.startTime).format(context)} - ${TimeOfDay.fromDateTime(appointment.endTime).format(context)}',
            style: const TextStyle(color: Colors.white, fontSize: 12),
          ),
        );
      },
    );
  }

  List<Appointment> _getDataSource() {
    final DateTime today = DateTime.now();
    return <Appointment>[
      Appointment(
        startTime: DateTime(today.year, today.month, today.day, 9),
        endTime: DateTime(today.year, today.month, today.day, 12),
        subject: 'Drag me!',
        color: Colors.blue,
      ),
    ];
  }
}

/// Simple data source to provide appointment data to the calendar
class _AppointmentDataSource extends CalendarDataSource {
  _AppointmentDataSource(List<Appointment> source) {
    appointments = source;
  }
}

Screenshots or Video

Screenshots / Video demonstration

Stack Traces

Stack Traces

doesn't apply here

On which target platforms have you observed this bug?

Web

Flutter Doctor output

Doctor output

[✓] Flutter (Channel stable, 3.44.2, on macOS 26.5.2 25F84 darwin-arm64, locale en-IT) [669ms]
    • Flutter version 3.44.2 on channel stable at /Users/work/fvm/versions/3.44.2
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision c9a6c48423 (6 weeks ago), 2026-06-10 15:52:41 -0700
    • Engine revision 77e2e94772
    • Dart version 3.12.2
    • DevTools version 2.57.0
    • Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop,
      enable-android, enable-ios, cli-animations, enable-native-assets, enable-swift-package-manager,
      omit-legacy-version-file, enable-lldb-debugging, enable-uiscene-migration

[✓] Android toolchain - develop for Android devices (Android SDK version 36.0.0) [1,585ms]
    • Android SDK at /Users/Shared/Android/sdk
    • Emulator version 36.6.11.0 (build_id 15507667) (CL:N/A)
    • Platform android-36, build-tools 36.0.0
    • ANDROID_HOME = /Users/Shared/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
      This is the JDK bundled with the latest Android Studio installation on this machine.
      To manually set the JDK path, use: `flutter config --jdk-dir="path/to/jdk"`.
    • Java version OpenJDK Runtime Environment (build 21.0.10+-117844308-b1163.108)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 26.5) [964ms]
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 17F42
    • CocoaPods version 1.16.2

[✓] Chrome - develop for the web [6ms]
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Connected device (4 available) [6.1s]
    (removed)

[✓] Network resources [282ms]
    • All expected network resources are available.

• No issues found!

[Mugunthan-Ramalingam]

Hi Felix,

Thank you for reporting this issue with the SfCalendar drag-and-drop functionality. We have reproduced the issue on our end, and a fix has been scheduled for our upcoming weekly release on August 04, 2026. We will notify you once the release is available. Thank you for your patience.

Root cause:
When timeIntervalHeight: -1 is used, the calendar auto-fits the entire day time slots within the available view height. During drag-and-drop, the boundary-clamping logic restricts the appointment to the calculated day-view bounds, causing appointments dragged near midnight to snap to an earlier start time instead of extending into the next day.

Regards,
Mugunthan.

[Mugunthan-Ramalingam]

Hi Felix,

The reported issue regarding appointment drag-and-drop behavior when using timeIntervalHeight: -1 in the SfCalendar has been analyzed, and a fix has been completed. However, we regret to inform you that, due to our ongoing Volume 2, 2026 service pack release activities, we are unable to include this fix in the weekly release scheduled for August 04, 2026.

We will prioritize this fix and include it in the next weekly patch release, which is scheduled for August 11, 2026. We will notify you once the release has been rolled out.

We appreciate your patience and understanding.

Regards,
Mugunthan.

[Harsha-SF4223]

Hi Felix,

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/34.2.3.

Root Cause:

When timeIntervalHeight: -1 is used, the calendar auto-fits the entire day time slots within the available view height. During drag-and-drop, the boundary-clamping logic restricts the appointment to the calculated day-view bounds, causing appointments dragged near midnight to snap to an earlier start time instead of extending into the next day.

Thank you for your patience and understanding. Please let us know if you need any assistance with the upgrade or have further questions.

Regards,
Harsha.

[WieFel]

@Harsha-SF4223 thank you for the notification and the fix.

I just tried it with the new version 34.2.3, and unfortunately now it seems that the drag&drop is even more broken than before.
Now, when moving a 3h appointment to any time of the day, e.g. to 11 AM, the calendar would always yield an offset dropping time, sometimes even of 30 minutes or more.

Here is a video of the behavior:
https://github.com/user-attachments/assets/7c70f789-14ba-4b79-bb57-c26b278a3b22

This can be reproduced with the example code from above, using syncfusion_flutter_calendar: ^34.2.3