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Flutter next pageView with button click

void main() => runApp(new PageDemo());

class PageDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(title: 'Page Demo', home: SamplePage());
  }
}

class SamplePage extends StatefulWidget {
  @override
  _SamplePageState createState() => _SamplePageState();
}

class _SamplePageState extends State<SamplePage> {
  List<Widget> _samplePages = [
    Center(
      child: Text('Page 1'),
    ),
    Center(child: Text('Page 2'))
  ];
  final _controller = new PageController();
  static const _kDuration = const Duration(milliseconds: 300);
  static const _kCurve = Curves.ease;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Page Demo'),
      ),
      body: Column(
        children: <Widget>[
          Flexible(
            child: PageView.builder(
              controller: _controller,
              itemCount: _samplePages.length,
              itemBuilder: (BuildContext context, int index) {
                return _samplePages[index % _samplePages.length];
              },
            ),
          ),
          Container(
            color: Colors.lightBlueAccent,
            child: Row(
              mainAxisSize: MainAxisSize.max,
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: <Widget>[
                FlatButton(
                  child: Text('Prev'),
                  onPressed: () {
                    _controller.previousPage(
                        duration: _kDuration, curve: _kCurve);
                  },
                ),
                FlatButton(
                  child: Text('Next'),
                  onPressed: () {
                    _controller.nextPage(duration: _kDuration, curve: _kCurve);
                  },
                )
              ],
            ),
          )
        ],
      ),
    );
  }
}

flutter pageview show next page

PageView(
  children: items,
  controller: PageController(
      viewportFraction: 0.8,
      initialPage: 0,
  )

)