Hot reload doesn't recognize change in length in DefaultTabController

When updating the DefaultTabController from the tutorial to a length of 4 instead of 3 and reloading, Flutter doesn't recognize that the length value has changed.
This is the code:

import 'package:flutter/material.dart';

void main() => runApp(new HeadacheApp());

class HeadacheApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: DefaultTabController(
        length: 4,
        child: Scaffold(
          appBar: AppBar(
            bottom: TabBar(
              tabs: [
                Tab(icon: Icon(Icons.directions_car)),
                Tab(icon: Icon(Icons.directions_transit)),
                Tab(icon: Icon(Icons.directions_bike)),
                Tab(icon: Icon(Icons.help)),
              ],
            ),
            title: Text('Tabs Demo'),
          ),
          body: TabBarView(
            children: [
              Icon(Icons.directions_car),
              Icon(Icons.directions_transit),
              Icon(Icons.directions_bike),
              Icon(Icons.help),
            ],
          ),
        ),
      ),
    );
  }
}

It gives the following error:

flutter: ══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
flutter: The following assertion was thrown while handling a gesture:
flutter: 'package:flutter/src/material/tab_controller.dart': Failed assertion: line 112 pos 12: 'value >= 0
flutter: && (value < length || length == 0)': is not true.
flutter:
flutter: Either the assertion indicates an error in the framework itself, or we should provide substantially
flutter: more information in this error message to help you determine and fix the underlying cause.
flutter: In either case, please report this assertion by filing a bug on GitHub:
flutter:   https://github.com/flutter/flutter/issues/new
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #2      TabController._changeIndex (package:flutter/src/material/tab_controller.dart)
flutter: #3      TabController.animateTo (package:flutter/src/material/tab_controller.dart:164:5)
flutter: #4      _TabBarState._handleTap (package:flutter/src/material/tabs.dart:864:17)
flutter: #5      _TabBarState.build.<anonymous closure> (package:flutter/src/material/tabs.dart:939:21)
flutter: #6      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:494:14)
flutter: #7      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:549:30)
flutter: #8      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:102:24)
flutter: #9      TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:161:9)
flutter: #10     TapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:94:7)
flutter: #11     PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:315:9)
flutter: #12     PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:73:12)
flutter: #13     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:11)
flutter: #14     _WidgetsFlutterBinding&BindingBase&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:143:19)
flutter: #15     _WidgetsFlutterBinding&BindingBase&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:121:22)
flutter: #16     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:101:7)
flutter: #17     _WidgetsFlutterBinding&BindingBase&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:64:7)
flutter: #18     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:48:7)
flutter: #19     _invoke1 (dart:ui/hooks.dart:134:13)
flutter: #20     _dispatchPointerDataPacket (dart:ui/hooks.dart:91:5)
flutter: (elided 2 frames from class _AssertionError)
flutter:
flutter: Handler: onTap
flutter: Recognizer:
flutter:   TapGestureRecognizer#8e887(debugOwner: GestureDetector, state: possible, won arena, finalPosition:
flutter:   Offset(329.3, 132.7), sent tap down)
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════

I went into flutter/src/material/tab_controller.dart and printed the values of length and value which were both 3 instead of 3 and 4, which caused the exception to be raised. I was able to fix this by restarting the iPhone simulator and re-uploading the app.

@cbracken

/cc @cbracken

@zachjanicki

@zachjanicki
Please add the output of flutter doctor

@rmacnak-google

/cc @rmacnak-google who IIRC looked into similar issues in the past (specifically detecting and warning about changes that aren't reloaded).

similar issue!
my code:

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

void main() => runApp(new MaterialApp(
    home: new MyApp(),
));

class MyApp extends StatefulWidget {
    @override
    _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
    List<String> _items;

    @override
    void initState() {
        super.initState();
        _items = ["item1", "item2", "item3"];

        new Future.delayed(const Duration(seconds: 2), () {
            setState(() {
                _items = ["item1", "item2", "item3", "item4", "item5"];
            });
        });
    }

    @override
    Widget build(BuildContext context) {
        return new DefaultTabController(
            length: _items.length,
            child: new Scaffold(
                appBar: new AppBar(
                    title: new Text("title"),
                    bottom: new TabBar(
                        tabs: _items.map((item) {
                            return new Tab(text: item);
                        }).toList(),
                    ),
                ),
                body: new TabBarView(
                    children: _items.map((item) {
                        return new Center(
                            child: new Text(item),
                        );
                    }).toList(),
                ),
            ),
        );
    }
}

after 2s, tap item4 and item5 throw exception:

18:29:36.747 10 800 flutter.tools I/flutter ( 7407): ══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
18:29:36.786 11 800 flutter.tools I/flutter ( 7407): The following assertion was thrown while handling a gesture:
18:29:36.786 12 800 flutter.tools I/flutter ( 7407): 'package:flutter/src/material/tab_controller.dart': Failed assertion: line 110 pos 12: 'value >= 0
18:29:36.786 13 800 flutter.tools I/flutter ( 7407): && (value < length || length == 0)': is not true.
18:29:36.808 14 800 flutter.tools I/flutter ( 7407): 
18:29:36.808 15 800 flutter.tools I/flutter ( 7407): Either the assertion indicates an error in the framework itself, or we should provide substantially
18:29:36.808 16 800 flutter.tools I/flutter ( 7407): more information in this error message to help you determine and fix the underlying cause.
18:29:36.808 17 800 flutter.tools I/flutter ( 7407): In either case, please report this assertion by filing a bug on GitHub:
18:29:36.808 18 800 flutter.tools I/flutter ( 7407):   https://github.com/flutter/flutter/issues/new
18:29:36.808 19 800 flutter.tools I/flutter ( 7407): 
18:29:36.815 20 800 flutter.tools I/flutter ( 7407): When the exception was thrown, this was the stack:
18:29:37.011 21 800 flutter.tools I/flutter ( 7407): #2      TabController._changeIndex (package:flutter/src/material/tab_controller.dart)
18:29:37.011 22 800 flutter.tools I/flutter ( 7407): #3      TabController.animateTo (package:flutter/src/material/tab_controller.dart:162:5)
18:29:37.011 23 800 flutter.tools I/flutter ( 7407): #4      _TabBarState._handleTap (package:flutter/src/material/tabs.dart:864:17)
18:29:37.011 24 800 flutter.tools I/flutter ( 7407): #5      _TabBarState.build.<anonymous closure> (package:flutter/src/material/tabs.dart:939:21)
18:29:37.012 25 800 flutter.tools I/flutter ( 7407): #6      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:494:14)
18:29:37.012 26 800 flutter.tools I/flutter ( 7407): #7      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:549:30)
18:29:37.012 27 800 flutter.tools I/flutter ( 7407): #8      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:102:24)
18:29:37.012 28 800 flutter.tools I/flutter ( 7407): #9      TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:161:9)
18:29:37.012 29 800 flutter.tools I/flutter ( 7407): #10     TapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:94:7)
18:29:37.012 30 800 flutter.tools I/flutter ( 7407): #11     PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:315:9)
18:29:37.012 31 800 flutter.tools I/flutter ( 7407): #12     PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:73:12)
18:29:37.012 32 800 flutter.tools I/flutter ( 7407): #13     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:11)
18:29:37.012 33 800 flutter.tools I/flutter ( 7407): #14     _WidgetsFlutterBinding&BindingBase&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:143:19)
18:29:37.012 34 800 flutter.tools I/flutter ( 7407): #15     _WidgetsFlutterBinding&BindingBase&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:121:22)
18:29:37.012 35 800 flutter.tools I/flutter ( 7407): #16     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:101:7)
18:29:37.012 36 800 flutter.tools I/flutter ( 7407): #17     _WidgetsFlutterBinding&BindingBase&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:64:7)
18:29:37.012 37 800 flutter.tools I/flutter ( 7407): #18     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:48:7)
18:29:37.012 38 800 flutter.tools I/flutter ( 7407): #19     _invoke1 (dart:ui/hooks.dart:134:13)
18:29:37.012 39 800 flutter.tools I/flutter ( 7407): #20     _dispatchPointerDataPacket (dart:ui/hooks.dart:91:5)
18:29:37.012 40 800 flutter.tools I/flutter ( 7407): (elided 2 frames from class _AssertionError)
18:29:37.012 41 800 flutter.tools I/flutter ( 7407): 
18:29:37.012 42 800 flutter.tools I/flutter ( 7407): Handler: onTap
18:29:37.012 43 800 flutter.tools I/flutter ( 7407): Recognizer:
18:29:37.012 44 800 flutter.tools I/flutter ( 7407):   TapGestureRecognizer#24d68(debugOwner: GestureDetector, state: possible, won arena, finalPosition:
18:29:37.012 45 800 flutter.tools I/flutter ( 7407):   Offset(286.5, 104.9), sent tap down)
18:29:37.012 46 800 flutter.tools I/flutter ( 7407): ════════════════════════════════════════════════════════════════════════════════════════════════════

flutter doctor:

[✓] Flutter (Channel dev, v0.5.7, on Mac OS X 10.13.5 17F77, locale zh-Hans-CN)
[✓] Android toolchain - develop for Android devices (Android SDK 27.0.3)
[✓] iOS toolchain - develop for iOS devices (Xcode 9.4.1)
[✓] Android Studio
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
[✓] IntelliJ IDEA Ultimate Edition (version 2018.1)
[✓] Connected devices (1 available)

• No issues found!

Is this related to #18481?

@matthew5025

@matthew5025 are you sure this is the link you intended to post. That doesn't look related to me.

@zoechi

@zoechi Apologies, it should have been #18481

Facing the same issue when adding a tab dynamically to the tab controller

The problem seems to be with using DefaultTabController, because it creates a TabController in its initState, and assigns it a length, which means the tab controller cannot change the length dynamically. To solve an issue similar to this, where I had to add extra tabs depending on certain conditions, I just used a custom TabController instead of the DefaultTabController

@AbdulRahmanAlHamali

This is not only a hot reload issue, the DefaultTabController / TabController does not support dynamic changing the length.

I meet the same issue, I need to dynamic changing the length of TabController when refreshing data from network. This is a product requirement.

@AbdulRahmanAlHamali How do you create a custom TabController? remember we need to call the dispose() method of a TabController, otherwise it will lead to memory leak.

I assign a ValueKey (using the length of tabs as value ) to the DefaultTabController, and it works correctly, because when the key changes, the Flutter wont reuse the current DefaultTabController.

This is a temp fix, hope this issue to be fixed ASAP.

@MaxZeng

@MaxZeng I just create a TabController inside the widget and assign it to the TabBar, and every time I want to change the number of tabs in the tab controller, I dispose of the old one and create a new one with the new number of tabs.

Is there any progress or ETA on this issue?

Is this issue still being worked on?

@AbdulRahmanAlHamali

the cause is exactly what @AbdulRahmanAlHamali said. Any update on this, I don't see the fix in v1.2.1 yet? @zoechi

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.

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Hot reload doesn't recognize change in length in DefaultTabController #18686

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Hot reload doesn't recognize change in length in DefaultTabController #18686

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zoechi commented on Jun 22, 2018

zoechi commented on Jun 22, 2018

cbracken commented on Jul 9, 2018

no-or-no commented on Jul 17, 2018

matthew5025 commented on Aug 3, 2018

zoechi commented on Aug 3, 2018

matthew5025 commented on Aug 4, 2018

AbdulRahmanAlHamali commented on Sep 6, 2018

AbdulRahmanAlHamali commented on Sep 26, 2018

flypigz commented on Jan 19, 2019

AbdulRahmanAlHamali commented on Jan 19, 2019

dbpprt commented on Feb 5, 2019

w4mxl commented on Mar 14, 2019

PandaGeek1024 commented on Mar 20, 2019

github-actions commented on Aug 30, 2021

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