AutomaticKeepAliveClientMixin for tabbar example

automatic_example.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage>
    with SingleTickerProviderStateMixin {
  TabController controller;

  @override
  void initState() {
    super.initState();
    controller = TabController(length: 4, vsync: this);
  }

  @override
  void dispose() {
    controller?.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      initialIndex: 0,
      child: Scaffold(
        appBar: AppBar(
          bottom: TabBar(
            controller: controller,
            tabs: <Widget>[
              Tab(text: "1"),
              Tab(text: "2"),
              Tab(text: "3"),
              Tab(text: "4"),
            ],
          ),
        ),
        body: TabBarView(
          controller: controller,
          children: <Widget>[
            SubPage(),
            SubPage(),
            SubPage(),
            SubPage(),
          ],
        ),
      ),
      length: 4,
    );
  }
}

class SubPage extends StatefulWidget {
  @override
  _SubPageState createState() => _SubPageState();
}

class _SubPageState extends State<SubPage> with AutomaticKeepAliveClientMixin {
  @override
  Widget build(BuildContext context) {
    super.build(context);
    return ListViewWidget();
  }

  @override
  bool get wantKeepAlive => true;
}

class ListViewWidget extends StatefulWidget {
  @override
  _ListViewWidgetState createState() => _ListViewWidgetState();
}

class _ListViewWidgetState extends State<ListViewWidget> {
  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      itemBuilder: _buildItem,
      itemCount: 50,
    );
  }

  Widget _buildItem(BuildContext context, int index) {
    return ListTile(
      title: Text(index.toString()),
    );
  }
}

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