How to jump to another page with pageview flutter

You can pass a callback to your first widget and call that when the button is pressed, so you can change the page in the parent widget. Something like this:

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Test',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Parent(),
    );
  }
}

class Parent extends StatefulWidget {
  @override
  _ParentState createState() => _ParentState();
}

class _ParentState extends State<Parent> {
  int bottomSelectedIndex = 0;

  List<BottomNavigationBarItem> buildBottomNavBarItems() {
    return [
      BottomNavigationBarItem(
          icon: new Icon(Icons.home), title: new Text('First')),
      BottomNavigationBarItem(
        icon: new Icon(Icons.search),
        title: new Text('Second'),
      ),
    ];
  }

  PageController pageController = PageController(
    initialPage: 0,
    keepPage: true,
  );

  Widget buildPageView() {
    return PageView(
      controller: pageController,
      onPageChanged: (index) {
        pageChanged(index);
      },
      children: <Widget>[
        FirstWidget(
          onButtonPressed: () => pageController.animateToPage(
                1,
                duration: Duration(milliseconds: 300),
                curve: Curves.linear,
              ),
        ),
        SecondWidget(),
      ],
    );
  }

  @override
  void initState() {
    super.initState();
  }

  void pageChanged(int index) {
    setState(() {
      bottomSelectedIndex = index;
    });
  }

  void bottomTapped(int index) {
    setState(() {
      bottomSelectedIndex = index;
      pageController.animateToPage(index,
          duration: Duration(milliseconds: 500), curve: Curves.ease);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Test'),
      ),
      body: buildPageView(),
      bottomNavigationBar: BottomNavigationBar(
        currentIndex: bottomSelectedIndex,
        onTap: (index) {
          bottomTapped(index);
        },
        items: buildBottomNavBarItems(),
      ),
    );
  }
}

class FirstWidget extends StatefulWidget {
  final VoidCallback onButtonPressed;

  FirstWidget({@required this.onButtonPressed});

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

class _FirstWidgetState extends State<FirstWidget> {
  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.red,
      child: Center(
        child: FlatButton(
          onPressed: widget.onButtonPressed,
          child: Text('Go to second page'),
        ),
      ),
    );
  }
}


class SecondWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(color: Colors.green);
  }
}

You can use this:

void onAddButtonTapped(int index) {

  // use this to animate to the page
  pageController.animateToPage(index);

  // or this to jump to it without animating
  pageController.jumpToPage(index);
}

Pass the function as params:

class first {
  final void Function(int) onAddButtonTapped;

        return Container(
// call it here onAddButtonTapped(2);
        );

    }

class Second {
  final void Function(int) onAddButtonTapped;

        return Container(
        );

    }

children: <Widget>[
        First(onAddButtonTapped),
        Second(onAddButtonTapped),
      ],