gistfile1.txt

// TabController with a single element fails assertion on horizontal tab scroll after number of tabs was decreased from 2 to 1
// https://github.com/flutter/flutter/issues/18481

import 'package:flutter/material.dart';

class TabControllerBug extends StatefulWidget {
  @override
  _TabControllerBugState createState() => new _TabControllerBugState();
}

class _TabControllerBugState extends State<TabControllerBug> with TickerProviderStateMixin {
  const List<Icon> icons1 = <Icon>[
    const Icon(Icons.android, semanticLabel: 'Android'),
  ];

  const List<Icon> icons2 = <Icon>[
    const Icon(Icons.event, semanticLabel: 'Event'),
    const Icon(Icons.home, semanticLabel: 'Home'),
  ];

  List<Icon> _icons;
  TabController _tabController;

  @override
  void initState() {
    _tabController = new TabController(length: 2, vsync: this);
    _icons = icons2;
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new Center(
        child: new Column(
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            new RaisedButton(
              child: const Text('reset _tabController, _icons'),
              onPressed: () {
                setState(() {
                  _tabController = new TabController(length: 1, vsync: this);
                  _icons = icons1;
                });
              },
            ),
            const SizedBox(height: 48.0),
            new SizedBox(
              height: 100.0,
              child: new TabBarView(
                controller: _tabController,
                children: _icons.map((Icon icon) {
                  return new Container(
                    padding: const EdgeInsets.all(12.0),
                    child: new Card(
                      child: new Center(
                        child: icon,
                      ),
                    ),
                  );
                }).toList()
              ),
            ),
            new TabPageSelector(controller: _tabController),
          ],
        ),
      ),
    );
  }
}

class TabControllerBugApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new TabControllerBug(),
    );
  }
}

void main() {
  runApp(new TabControllerBugApp());
}