import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';
import 'package:shared_preferences/shared_preferences.dart';

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

class CupertinoTabs extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
        home: new CupertinoTabScaffold(
            tabBar: new CupertinoTabBar(
              items: [
                new BottomNavigationBarItem(
                  icon: new Icon(Icons.list),
                  title: new Text("Posts"),
                ),
                new BottomNavigationBarItem(
                  icon: new Icon(Icons.loyalty),
                  title: new Text("Tags"),
                ),
                new BottomNavigationBarItem(
                  icon: new Icon(Icons.calendar_today),
                  title: new Text("Calendar"),
                ),
                new BottomNavigationBarItem(
                  icon: new Icon(Icons.location_on),
                  title: new Text("Locations"),
                ),
              ],
            ),
            tabBuilder: (BuildContext context, int index) {
              return new CupertinoTabView(builder: (BuildContext context) {
                return new CupertinoPageScaffold(
                  navigationBar: new CupertinoNavigationBar(
                      middle: new Text("${index+1} tab")),
                  child: new Counter(index),
                );
              });
            }));
  }
}

class Counter extends StatefulWidget {
  Counter(this.index, {Key key}) : super(key: key);

  final int index;

  @override
  CounterState createState() => new CounterState();
}

class CounterState extends State<Counter> {
  int counter = 0;


  void incrementCounter() async {
    setState(() {
      counter++;
    });

    SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.setInt('counter${widget.index}', counter);
    print("saved counter: $counter for index: ${widget.index}");
  }

  void setCounterFromPrefs() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    int counterValue = prefs.getInt('counter${widget.index}') ?? 0;

    setState(() {
      counter = counterValue;
    });
  }

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

  @override
  Widget build(BuildContext context) {
    return new Center(
      child: new Column(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: <Widget>[
          new Text('Counter value: $counter'),
          new CupertinoButton(
              child: const Text("Increment counter"),
              color: CupertinoColors.activeBlue,
              onPressed: () {
                incrementCounter();
              }),
        ],
      ),
    );
  }
}