How to create a dynamic TabBarView/ Render a new Tab with a function in Flutter?

Problems arise if you need to modify the arrays. They consist in the fact that when modifying an array you do not have the opportunity to use the same controller.

You can use the next custom widget for this case:

import 'package:flutter/material.dart';
  
void main() => runApp(MyApp());
 

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

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

class MyHomePageState extends State<MyHomePage> {
  List<String> data = ['Page 0', 'Page 1', 'Page 2'];
  int initPosition = 1;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: CustomTabView(
          initPosition: initPosition,
          itemCount: data.length,
          tabBuilder: (context, index) => Tab(text: data[index]),
          pageBuilder: (context, index) => Center(child: Text(data[index])),
          onPositionChange: (index) {
            print('current position: $index');
            initPosition = index;
          },
          onScroll: (position) => print('$position'),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {
            data.add('Page ${data.length}');
          });
        },
        child: const Icon(Icons.add),
      ),
    );
  }
}

class CustomTabView extends StatefulWidget {
  const CustomTabView({
    super.key,
    required this.itemCount,
    required this.tabBuilder,
    required this.pageBuilder,
    this.stub,
    this.onPositionChange,
    this.onScroll,
    this.initPosition,
  });

  final int itemCount;
  final IndexedWidgetBuilder tabBuilder;
  final IndexedWidgetBuilder pageBuilder;
  final Widget? stub;
  final ValueChanged<int>? onPositionChange;
  final ValueChanged<double>? onScroll;
  final int? initPosition;

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

class CustomTabsState extends State<CustomTabView>
    with TickerProviderStateMixin {
  late TabController controller;
  late int _currentCount;
  late int _currentPosition;

  @override
  void initState() {
    _currentPosition = widget.initPosition ?? 0;
    controller = TabController(
      length: widget.itemCount,
      vsync: this,
      initialIndex: _currentPosition,
    );
    controller.addListener(onPositionChange);
    controller.animation!.addListener(onScroll);
    _currentCount = widget.itemCount;
    super.initState();
  }

  @override
  void didUpdateWidget(CustomTabView oldWidget) {
    if (_currentCount != widget.itemCount) {
      controller.animation!.removeListener(onScroll);
      controller.removeListener(onPositionChange);
      controller.dispose();

      if (widget.initPosition != null) {
        _currentPosition = widget.initPosition!;
      }

      if (_currentPosition > widget.itemCount - 1) {
        _currentPosition = widget.itemCount - 1;
        _currentPosition = _currentPosition < 0 ? 0 : _currentPosition;
        if (widget.onPositionChange is ValueChanged<int>) {
          WidgetsBinding.instance.addPostFrameCallback((_) {
            if (mounted && widget.onPositionChange != null) {
              widget.onPositionChange!(_currentPosition);
            }
          });
        }
      }

      _currentCount = widget.itemCount;
      setState(() {
        controller = TabController(
          length: widget.itemCount,
          vsync: this,
          initialIndex: _currentPosition,
        );
        controller.addListener(onPositionChange);
        controller.animation!.addListener(onScroll);
      });
    } else if (widget.initPosition != null) {
      controller.animateTo(widget.initPosition!);
    }

    super.didUpdateWidget(oldWidget);
  }

  @override
  void dispose() {
    controller.animation!.removeListener(onScroll);
    controller.removeListener(onPositionChange);
    controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    if (widget.itemCount < 1) return widget.stub ?? Container();

    return Column(
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: <Widget>[
        Container(
          alignment: Alignment.center,
          child: TabBar(
            isScrollable: true,
            controller: controller,
            labelColor: Theme.of(context).primaryColor,
            unselectedLabelColor: Theme.of(context).hintColor,
            indicator: BoxDecoration(
              border: Border(
                bottom: BorderSide(
                  color: Theme.of(context).primaryColor,
                  width: 2,
                ),
              ),
            ),
            tabs: List.generate(
              widget.itemCount,
              (index) => widget.tabBuilder(context, index),
            ),
          ),
        ),
        Expanded(
          child: TabBarView(
            controller: controller,
            children: List.generate(
              widget.itemCount,
              (index) => widget.pageBuilder(context, index),
            ),
          ),
        ),
      ],
    );
  }

  void onPositionChange() {
    if (!controller.indexIsChanging) {
      _currentPosition = controller.index;
      if (widget.onPositionChange is ValueChanged<int>) {
        widget.onPositionChange!(_currentPosition);
      }
    }
  }

  void onScroll() {
    if (widget.onScroll is ValueChanged<double>) {
      widget.onScroll!(controller.animation!.value);
    }
  }
}