TrainHoppingAnimation Calls notifyListeners() on Status Change Instead of notifyStatusListeners()

In its animation status listener, TrainHoppingAnimation calls notifyListeners() on status change when it should call notifyStatusListeners().

flutter/packages/flutter/lib/src/animation/animations.dart

Lines 542 to 550 in b1d5f03

    
           AnimationStatus? _lastStatus; 
        
           void _statusChangeHandler(AnimationStatus status) { 
        
             assert(_currentTrain != null); 
        
             if (status != _lastStatus) { 
        
               notifyListeners(); 
        
               _lastStatus = status; 
        
             } 
        
             assert(_lastStatus != null); 
        
           }

Code sample

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Screen(),
    );
  }
}

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

  @override
  State<Screen> createState() => _ScreenState();
}

class _ScreenState extends State<Screen> with SingleTickerProviderStateMixin {
  late final _controller = AnimationController(
    vsync: this,
    duration: const Duration(seconds: 3),
  );

  late final _animation = TrainHoppingAnimation(
    Tween<double>(begin: 1, end: 0).animate(_controller),
    Tween<double>(begin: 0, end: 1).animate(_controller),
  );

  @override
  void initState() {
    super.initState();
    _controller.addStatusListener((status) {
      print('controller: $status');
    });
    _animation.addStatusListener((status) {
      print('animation: $status');
    });
    _controller.forward();
  }

  @override
  void dispose() {
    _animation.dispose();
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: ScaleTransition(
        scale: _animation,
        child: Container(
          color: Colors.red,
          height: 200,
          width: 200,
        ),
      ),
    );
  }
}

@swrenn

@swrenn Can you provide us a code example that shows the current behavior versus expected behavior ?
Below is a sample code based on the issue you described it shortly:

runnable code


import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Train Hopping Animation',
      theme: ThemeData(
        useMaterial3: true,
        primarySwatch: Colors.blueGrey,
      ),
      home: const TrainHoppingScreen(),
    );
  }
}

// 1. Define the Stateful Widget and Ticker Provider
class TrainHoppingScreen extends StatefulWidget {
  const TrainHoppingScreen({super.key});

  @override
  State<TrainHoppingScreen> createState() => _TrainHoppingScreenState();
}

// 2. Use SingleTickerProviderStateMixin for the AnimationController
class _TrainHoppingScreenState extends State<TrainHoppingScreen> with SingleTickerProviderStateMixin {
  late AnimationController _controller;
  late Animation<double> _hopAnimation;

  String _statusMessage = 'Initializing...';

  @override
  void initState() {
    super.initState();

    // Initialize the AnimationController
    _controller = AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 800), // Time for one hop
    );

    // Create the animation: a vertical movement from 0.0 to -100.0 (upwards hop)
    // The value 100.0 is used as a multiplier for the hop distance.
    _hopAnimation = Tween<double>(begin: 0.0, end: -100.0).animate(
      // Apply a smooth bounce curve to the animation
      CurvedAnimation(
        parent: _controller,
        curve: Curves.easeOut,
      ),
    );

    // 3. Add Status Listener to the AnimationController
    // This is the core requirement: listening to the animation status.
    _controller.addStatusListener((status) {
      if (status == AnimationStatus.completed) {
        // When the hop is complete (reached the peak), reverse the animation
        _controller.reverse();
        setState(() {
          _statusMessage = 'Hop Completed. Reversing...';
        });
      } else if (status == AnimationStatus.dismissed) {
        // When the hop is dismissed (back on the ground), repeat the animation
        _controller.forward();
        setState(() {
          _statusMessage = 'Landed. Starting next Hop!';
        });
      } else if (status == AnimationStatus.forward) {
        setState(() {
          _statusMessage = 'Hopping Forward...';
        });
      } else if (status == AnimationStatus.reverse) {
        setState(() {
          _statusMessage = 'Descending (Reverse)...';
        });
      }
      // Print to console to show real-time status changes
      print('Animation Status: $status');
    });

    // Start the animation immediately
    _controller.forward();
  }

  @override
  void dispose() {
    // Clean up the controller when the widget is disposed
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Train Hopper Demo'),
        backgroundColor: Colors.blueGrey,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            // Display the current animation status
            Padding(
              padding: const EdgeInsets.all(16.0),
              child: Text(
                'Status: $_statusMessage',
                style: const TextStyle(fontSize: 18, fontWeight: FontWeight.w600),
                textAlign: TextAlign.center,
              ),
            ),
            const SizedBox(height: 50),

            // 4. Use AnimatedBuilder to apply the animation value
            AnimatedBuilder(
              animation: _hopAnimation,
              builder: (context, child) {
                // Apply a vertical translation based on the animation value
                return Transform.translate(
                  offset: Offset(0, _hopAnimation.value),
                  child: child,
                );
              },
              child: Container(
                width: 150,
                height: 80,
                decoration: BoxDecoration(
                  color: Colors.red[700],
                  borderRadius: BorderRadius.circular(12),
                  boxShadow: [
                    BoxShadow(
                      color: Colors.black.withOpacity(0.3),
                      spreadRadius: 2,
                      blurRadius: 5,
                      offset: const Offset(0, 5),
                    ),
                  ],
                ),
                child: const Center(
                  child: Text(
                    'The Hopper',
                    style: TextStyle(color: Colors.white, fontWeight: FontWeight.bold),
                  ),
                ),
              ),
            ),
            const SizedBox(height: 10),
            // "Train" element to hop next to
            Container(
              width: 250,
              height: 50,
              decoration: BoxDecoration(
                color: Colors.blueGrey[900],
                borderRadius: BorderRadius.circular(8),
              ),
              child: const Center(
                child: Text(
                  'The Train ',
                  style: TextStyle(color: Colors.white, fontWeight: FontWeight.bold),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

which prints below:

flutter: Animation Status: AnimationStatus.forward
flutter: Animation Status: AnimationStatus.reverse
flutter: Animation Status: AnimationStatus.completed
flutter: Animation Status: AnimationStatus.forward
flutter: Animation Status: AnimationStatus.dismissed
flutter: Animation Status: AnimationStatus.reverse
flutter: Animation Status: AnimationStatus.completed
flutter: Animation Status: AnimationStatus.forward

Please check if above correctly interprets the issue you are reporting or please update it to show current behavior as compared to expected.

@darshankawar

Hi @darshankawar, thanks a lot for taking a look at this issue. I've added a code sample to the issue. May I ask you to try it?

@ksokolovskyi

Thanks @ksokolovskyi for the code. With it, I get below which doesn't seem to notify all statuses.

flutter: controller: AnimationStatus.forward
flutter: controller: AnimationStatus.completed

While https://api.flutter.dev/flutter/animation/AnimationLocalStatusListenersMixin/notifyStatusListeners.html does mention that it calls all status listeners, so ideally it should be called instead of notifyListeners.

Fix train hopping animation status listeners (#178372)

Fix train hopping animation status listeners (flutter#178372)

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

Fix train hopping animation status listeners (flutter#178372)

Fix train hopping animation status listeners (#178372)

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TrainHoppingAnimation Calls notifyListeners() on Status Change Instead of notifyStatusListeners() #178336

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	AnimationStatus? _lastStatus;
	void _statusChangeHandler(AnimationStatus status) {
	assert(_currentTrain != null);
	if (status != _lastStatus) {
	notifyListeners();
	_lastStatus = status;
	}
	assert(_lastStatus != null);
	}

TrainHoppingAnimation Calls notifyListeners() on Status Change Instead of notifyStatusListeners() #178336

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darshankawar commented on Nov 12, 2025

ksokolovskyi commented on Nov 12, 2025

darshankawar commented on Nov 12, 2025

github-actions commented on Dec 3, 2025

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