import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  MyApp({Key key}) : super(key: key);

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

class _MyAppState extends State<MyApp> {
  PageController _pageController;
  ScrollController _scrollController;
  double offset = 0.0;

  @override
  void initState(){
    super.initState();
    _pageController = PageController(initialPage: 0);
    _scrollController = ScrollController();
    _scrollController.addListener(this.swapPageListener);
  }

  void swapPageListener() {
    WidgetsBinding.instance.addPostFrameCallback((_){ 
      offset = _scrollController.offset;
      // _pageController.hasClients
      if (offset > _scrollController.position.maxScrollExtent + 100) {
        if(_pageController.hasClients) {
          _pageController.animateToPage(1, duration: Duration(milliseconds: 500), curve: Curves.easeInOut);
          // _pageController.animateTo(offset, duration: duration, curve: curve)
        }
      }
      if (offset < _scrollController.position.minScrollExtent - 100) {
        _pageController.previousPage(duration: Duration(milliseconds: 500), curve: Curves.easeInOut);
      }
    });
  }
  // @override
  // void dispose() {
  //   super.dispose();
  //   _pageController.dispose();
  // }
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: PageView.builder(
          controller: _pageController,
          scrollDirection: Axis.vertical,
          itemCount: 2,
          physics: NeverScrollableScrollPhysics(),
          itemBuilder: (context, idx) {
            if(idx == 0) {
              return _screen1();
            } else {
              return _screen2();
            }
          }
        ),
      ),
    );
  }

  Widget _screen1() {
    return SingleChildScrollView(
      physics: BouncingScrollPhysics(),
      controller: _scrollController,
      child: Container(
        height: 1000.0,
        color: Colors.red,
        child: Center(
          child: Text('screen 1'),
        ),
      ),
    );
  }

  Widget _screen2() {
    return SingleChildScrollView(
      physics: BouncingScrollPhysics(),
      controller: _scrollController,
      child: Container(
        height: 1000.0,
        color: Colors.green,
        child: Center(
          child: Text('screen 2'),
        ),
      ),
    );
  }
}

[√] Flutter (Channel stable, 2.0.4, on Microsoft Windows [Version 10.0.19042.928], locale en-US)
    • Flutter version 2.0.4 at C:\src\flutter
    • Framework revision b1395592de (2 weeks ago), 2021-04-01 14:25:01 -0700
    • Engine revision 2dce47073a
    • Dart version 2.12.2

[!] Android toolchain - develop for Android devices (Android SDK version 30.0.1)
    • Android SDK at C:\Users\Admin\AppData\Local\Android\Sdk
    • Platform android-30, build-tools 30.0.1
    • ANDROID_HOME = C:\Users\Admin\AppData\Local\Android\Sdk
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)
    X Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/docs/get-started/install/windows#android-setup for more details.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 4.0)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 47.1.2
    • Dart plugin version 193.7547
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[√] VS Code (version 1.55.2)
    • VS Code at C:\Users\Admin\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.21.0

[√] Connected device (3 available)
    • Android SDK built for x86 64 (mobile) • emulator-5554 • android-x64    • Android 9 (API 28) (emulator)
    • Chrome (web)                          • chrome        • web-javascript • Google Chrome 87.0.4280.88
    • Edge (web)                            • edge          • web-javascript • Microsoft Edge 89.0.774.77

! Doctor found issues in 1 category.

ScrollController attached to multiple scroll views.
'package:flutter/src/widgets/scroll_controller.dart':
Failed assertion: line 109 pos 12: '_positions.length == 1'