I am trying to use tab controller in flutter how can I access it inside the build context

Just declare the tabController globally inside your state class and initialise it inside init state as you did, then you can access it inside your build method.

late TabController tabController;

void initState(){
   tabController=TabController(vsync:this,length:3); 
}
 

now use accordingly tab controller inside build method.

Try to declare tabController globally inside your state class and init it inside init state see the documentation for more details :

class _JobApplication... extendes State<...> ..{

   late TabController _tabController;

  @override
  void initState() {
    super.initState();
    _tabController = TabController(vsync: this, length: 3);
  }

}

declare in state

late TabController _tabController;

Assign in initstate

@override
  void initState() {
    super.initState();
    _tabController = TabController(vsync: this, length: 3);
  }