DynamicTabsGlobalKey.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(
    home: MyHomePage(title: 'Dynamic Tabs'),
  ));
}

class MyList extends StatefulWidget {
  final key;

  const MyList({this.key}) : super(key: key);

  @override
  _MyListState createState() => _MyListState();
}

class _MyListState extends State<MyList> {
  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      itemCount: 30,
      itemBuilder: (context, index) => ListTile(title: Text( "${widget.key.toString().substring(14)}: $index" ,))
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {

  TabController _tabController;

  final gKey_Tab0 = GlobalKey<_MyListState>();
  final gKey_Tab1 = GlobalKey<_MyListState>();
  
  List<Tab> _tabs = <Tab>[];

  _update_tabs_and_controller( newSize ){

    _tabs = <Tab>[
      if (newSize>0) Tab(key: Key("Tab0"),   text: "Tab0",),
      if (newSize>1) Tab(key: Key("Tab1"),   text: "Tab1",),
      if (newSize>2) Tab(key: Key("Tab2"),   text: "Tab2",),
      if (newSize>3) Tab(key: Key("Tab3"),   text: "Tab3",),
    ].where((t)=>t!=null).toList();

    _tabController = TabController(vsync: this, length: _tabs.length);
  }

  @override
  void initState() {
    
    _tabController = TabController(vsync: this, length: 0);

    Future.delayed(Duration(milliseconds: 500)).then((_) {
      setState(() {
        _update_tabs_and_controller(2);
      });
    });

    super.initState();
  }

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

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(

        title: Text(widget.title),
      ),
      body: TabBarView(
        //physics: NeverScrollableScrollPhysics(),
        controller: _tabController,
        children: <Widget>[
          if (_tabs.any((tab)=>tab.key==Key("Tab0"))) MyList(key: gKey_Tab0),
          if (_tabs.any((tab)=>tab.key==Key("Tab1"))) MyList(key: gKey_Tab1,),
          if (_tabs.any((tab)=>tab.key==Key("Tab2"))) MyList(key: Key("Tab2"),),
          if (_tabs.any((tab)=>tab.key==Key("Tab3"))) MyList(key: Key("Tab3"),),
        ].where((t)=>t!=null).toList(),
      ),

      bottomNavigationBar: TabBar(
        labelColor: Colors.black,
        indicatorSize: TabBarIndicatorSize.tab,
        tabs: _tabs,
        controller: _tabController,
      ),

      floatingActionButton: FloatingActionButton(
        onPressed: (){
          setState(() {
            // Switch tabs: 2->1
            _update_tabs_and_controller(1);
          });
        },
        child: Icon(Icons.remove),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}