How To Detect With New Tab Is Opened In Flutter Android App

import 'package:flutter/material.dart';

void main(){
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with SingleTickerProviderStateMixin {
  TabController _tabController;
  GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

  @override
  void initState() {
    super.initState();
    _aListener() {
      setState(() {
        if (_tabController.indexIsChanging) {
          _scaffoldKey.currentState.showSnackBar(SnackBar(
            content: Text("Tabbar Opening"),
          ));
        }
      });
    }

    _tabController = TabController(
      length: 2,
      vsync: this,
      initialIndex: 0,
    )..addListener(_aListener);
  }

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldKey,
      appBar: AppBar(
        backgroundColor: Colors.pink,
        title: Text("Detect Tabbar Open"),
        bottom: TabBar(
          controller: _tabController,
          tabs: <Widget>[
            Tab(
              text: "First Tab",
            ),
            Tab(
              text: "Second Tab",
            ),
          ],
        ),
      ),
      body: TabBarView(
        controller: _tabController,
        children: <Widget>[
          Center(
            child: Text("First Tab"),
          ),
          Center(
            child: Text("Second Tab"),
          ),
        ],
      ),
    );
  }
}