Axis change bug

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MaterialApp(home: MyApp()));

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

  static bool _slider = true;
  static List<Widget> _widgets = [
    Container(color: Colors.red,),
    Container(color: Colors.blue,),
    Container(color: Colors.green,),
  ];

  @override
  Widget build(BuildContext context)=> Scaffold(
    body: Center(
      child: PageView.builder(
      scrollDirection: _slider ? Axis.vertical : Axis.horizontal,
      itemCount: _widgets.length,
      itemBuilder: (BuildContext context, int index)=>
        _widgets[index],), 
    ),
    floatingActionButton: FloatingActionButton(
      onPressed: ()=> setState(()=> _slider = _slider ? false : true,)
    ),
  );
}