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TabController scroll exception when deleting tabs in a dynamic tab layout #24424
Description
When there are two tabs left and you delete the second tab, TabController throws an exception complaining it can not perform scroll animation when length<2, which is reasonable (I'm not complaining about this). However this exception cannot be avoided with regular methods as far as I know.
If you delete the first one, since there is no scroll animation, it's perfectly fine. TabController.animateTo(index-1) before deletion could have solved this exception, but it didn't. Since the animation is apparently async and is performed after the code complete.
It causes some burden when developing app with dynamic tabs. Right now TabController seems not quite fit into this scenario. Or is it I'm using it the wrong way and there's better way to implement this? Please let me know.
Steps to Reproduce
- Run the demo code below
- Create a few tabs, like "0", "1", "2", "3"
- Delete tabs from back to front. Delete "3", "2", "1"
- When deleting "1", the exception is thrown
- tabController.animateTo(pos-1) has no effect, until a delay is introduced (see in the demo code).
Logs
I/flutter ( 5137): The following assertion was thrown while notifying listeners for AnimationController:
I/flutter ( 5137): 'package:flutter/src/material/tab_controller.dart': Failed assertion: line 175 pos 12: 'length > 1':
I/flutter ( 5137): is not true.
...
I/flutter ( 5137): When the exception was thrown, this was the stack:
I/flutter ( 5137): #2 TabController.offset= (package:flutter/src/material/tab_controller.dart:175:12)
I/flutter ( 5137): #3 _TabBarViewState._handleScrollNotification (package:flutter/src/material/tabs.dart:1173:19)
Demo code (main.dart)
import 'package:flutter/material.dart';
import 'dart:async';
void main() => runApp(MyApp());
class MyApp extends StatefulWidget {
@override MyAppState createState() => MyAppState();
}
class MyAppState extends State<MyApp> with TickerProviderStateMixin {
List<Tab> tabs = [];TabController tabController;var count = 1;
void newTab() {
setState(() {
tabs.add(Tab(text: '$count',));count++;
tabController = TabController(length: tabs.length, vsync: this);
});
}
void closeCurrentTab() {
final pos=tabController.index;
setState((){
if(pos>0)
tabController.animateTo(pos-1);//This COULD have solved the problem.
});
//However, a delay must be introduced in order to let animateTo take effect. Uncomment to let delay take effect.
//Timer(kTabScrollDuration,(){
setState(() {
tabs.removeAt(pos);
tabController = TabController(initialIndex: pos-1,length: tabs.length, vsync: this);
});
//});
}
@override void initState() {
super.initState();
tabs.add(Tab(text: '0',));
tabController = TabController(length: tabs.length, vsync: this);
}
@override void dispose() {
tabController.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
actions: <Widget>[
IconButton(icon: Icon(Icons.add), onPressed: newTab),
IconButton(icon: Icon(Icons.close), onPressed: closeCurrentTab,)
],
bottom: TabBar(controller: tabController, tabs: tabs.map((tab) => tab).toList()),
),
body: TabBarView(controller: tabController, children: tabs.map((tab) => Text(tab.text)).toList()),
),
);
}
}
Activity
zoechi commentedon Nov 19, 2018
Please add the output of
flutter doctor -v.zoechi commentedon Nov 19, 2018
#23077, #20292, #18686, #16292 looks somewhat related.
Merging with #18481
ZhennanWu commentedon Nov 19, 2018
Good, seems I'm not the only one. #18481 is identical to this issue.
HansMuller commentedon Nov 30, 2018
This bug is not a duplicate of #18481, which has been fixed.
HansMuller commentedon Nov 30, 2018
This bug can be worked around for now by only resetting the tab controller after it has stopped changing. Here's a version of the original test case that does that: https://gist.github.com/HansMuller/15d7f306139ec92e5ecefb58f85a3d3f
HansMuller commentedon Nov 30, 2018
This is a simplified version of the test case. It still possible to make it trip the length assert (apparently due to a pending TabBarView scroll being handled after the tab controller has been replaced) but, FWIW, it's much more difficult to make it fail.
https://gist.github.com/HansMuller/37abc036d293bfc3ca27b943127a5689
HansMuller commentedon Dec 3, 2018
There's a fix for the bug here: #24892
HansMuller commentedon Dec 12, 2018
Fixed in #24892
github-actions commentedon Aug 14, 2021
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 -vand a minimal reproduction of the issue.