How to use TabController

Question

I just learned flutter, I was confused how to use the TabController, I had followed what was described on the official website, but an error appeared, and I don't know how to fix it.

I just want to change the title and leading from the appbar when changing tabs.

final List<ChangeTitleAndLeading> _data = [
  new ChangeTitleAndLeading(title: "Home", leading: Icon(Icons.home)),
  new ChangeTitleAndLeading(title: "Profile", leading: Icon(Icons.person)),
  new ChangeTitleAndLeading(title: "Friends", leading: Icon(Icons.people))
];

ChangeTitleAndLeading _handler;
TabController _controller;

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

  _checkEmailVerification();

  _controller = TabController(vsync: this, length: 3);
  _handler = _data[0];
  _controller.addListener(_handleSelected);
}

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

void _handleSelected() {
  setState(() {
    _handler = _data[_controller.index];
  });
}

return MaterialApp(
  theme: new ThemeData(
    primarySwatch: Colors.teal,
  ),
  home: new Scaffold(
    appBar: new AppBar(
      leading: Icon(Icons.home),
      title: new Text("Home"),
      bottom: new TabBar(
        controller: _controller,
        tabs: _tabs,
      ),
    ),

    body: TabBarView(
      controller: _controller,
      children: _pages,
    ),

    floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: () {
          print('Current Index: ${_handler.title}');
        }
    ),

class ChangeTitleAndLeading {
  final String title;
  final Widget leading;

  ChangeTitleAndLeading({
    @required this.title,
    @required this.leading
  }) :
    assert(title != null),
    assert(leading != null);
}

Error log:

Error Log: I/flutter (19638): No TabController for TabBarView. I/flutter (19638): When creating a TabBarView, you must either provide an explicit TabController using the "controller" I/flutter (19638): property or you must ensure that there is a DefaultTabController above the TabBarView. I/flutter (19638): In this case, there was neither an explicit controller nor a default controller. ════════════════════════════════════════════════════════════════════════════════════════════════════

I/flutter (19638): Another exception was thrown: No TabController for TabBar.

And when i change this: leading: Icon(Icons.home), to leading: _handler.leading, and this: title: new Text("Home"), to title: new Text(_handler.title), always return error _handler.leading or _handler.title was null

Image

Answer 1

The issue is that you are missing a tabbarcontroller

Your code should be:

return MaterialApp(
  theme: new ThemeData(
    primarySwatch: Colors.teal,
  ),
  home: DefaultTabController(
    length: 3,
    child: new Scaffold(
      appBar: new AppBar(
        leading: Icon(Icons.home),
        title: new Text("Home"),
        bottom: new TabBar(
          controller: _controller,
          tabs: _tabs,
        ),
      ),
      body: TabBarView(
        controller: _controller,
        children: _pages,
      )...