Force TabController to create all tabs Flutter - flutter

Question

I have a default page with two tabs, using TabBar and TabController. All is working fine, except when I enter the page, the second tab's build method is only called when I click to change to the second tab. The problem is that when I enter the page I want both tabs to be already created (a.k.a their build methods executed). Any thoughts?
Illustration code:
//This widget is used inside a Scaffold
class TabsPage extends StatefulWidget {
#override
State<StatefulWidget> createState() => new TabsPageState();
}
class TabsPageState extends State<TabsPage> with TickerProviderStateMixin {
List<Tab> _tabs;
List<Widget> _pages;
TabController _controller;
#override
void initState() {
super.initState();
_tabs = [
new Tab(text: 'TabOne'),
new Tab(text: 'TabTwo')
];
_pages = [
//Just normal stateful widgets
new TabOne(),
new TabTwo()
];
_controller = new TabController(length: _tabs.length, vsync: this);
}
#override
Widget build(BuildContext context) {
return new Padding(
padding: EdgeInsets.all(10.0),
child: new Column(
children: <Widget>[
new TabBar(
controller: _controller,
tabs: _tabs
),
new SizedBox.fromSize(
size: const Size.fromHeight(540.0),
child: new TabBarView(
controller: _controller,
children: _pages
),
)
],
),
);
}
}

Answer 1

I had a similar issue, I'm using Tabs with Forms and I wanted to validate all of them, my solution was to switch to the second tab programmatically, It doesn't make sense to not visit a tab with a form that requires validation.
So given a global key for each form:
final _formKey = GlobalKey<FormState>();
The reason I wanted all tabs to be built was to use:
_formKey.currentState.validate()
So my fix is
if (_formKey.currentState == null) { //The tab was never visited, force it
_tabController.animateTo(1);
return;
}

Answer 2

I was able to achieve this.
In my case, I had 2 tabs and I wanted to preload the other tab.
So what I did was, I initialised the tab controller in initState like this:
tabController = TabController(
length: 2,
vsync: this,
initialIndex: 1,
);
I set the initialIndex to the other tabs index, and then set the index back in after the build was done like this:
WidgetsBinding.instance.addPostFrameCallback((_) {
tabController.index = 0;
});
But this may only work if you have 2 tabs