counter with sharedpreferences

import 'dart:async';

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

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new 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 press Run > Flutter Hot Reload in IntelliJ). Notice that the
        // counter didn't reset back to zero; the application is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {

  Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
  Future<int> _counter;
  int counterx;

  Future<Null> _incrementCounter() async {
    final SharedPreferences prefs = await _prefs;
    final int counter = (prefs.getInt('counter') ?? 0) + 1;

    setState(() {
      _counter = prefs.setInt("counter", counter).then((bool success) {
        return counter;
      });
    });
  }

   @override
      void initState() {
        super.initState();
      _prefs.then(ambilNilai);
          }

        // void _incrementCounter() {
        //   setState(() {
        //     // This call to setState tells the Flutter framework that something has
        //     // changed in this State, which causes it to rerun the build method below
        //     // so that the display can reflect the updated values. If we changed
        //     // _counter without calling setState(), then the build method would not be
        //     // called again, and so nothing would appear to happen.
        //     _counter++;
        //   });
        // }

        @override
        Widget build(BuildContext context) {
          // This method is rerun every time setState is called, for instance as done
          // by the _incrementCounter method above.
          //
          // The Flutter framework has been optimized to make rerunning build methods
          // fast, so that you can just rebuild anything that needs updating rather
          // than having to individually change instances of widgets.
          return new Scaffold(
            appBar: new AppBar(
              // Here we take the value from the MyHomePage object that was created by
              // the App.build method, and use it to set our appbar title.
              title: new Text(widget.title),
            ),
            body: new Center(
              // Center is a layout widget. It takes a single child and positions it
              // in the middle of the parent.
              child: new Column(
                // Column is also layout widget. It takes a list of children and
                // arranges them vertically. By default, it sizes itself to fit its
                // children horizontally, and tries to be as tall as its parent.
                //
                // Invoke "debug paint" (press "p" in the console where you ran
                // "flutter run", or select "Toggle Debug Paint" from the Flutter tool
                // window in IntelliJ) to see the wireframe for each widget.
                //
                // Column has various properties to control how it sizes itself and
                // how it positions its children. Here we use mainAxisAlignment to
                // center the children vertically; the main axis here is the vertical
                // axis because Columns are vertical (the cross axis would be
                // horizontal).
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Text(counterx.toString()),
                ]
              ),
            ),
            floatingActionButton: new FloatingActionButton(
              onPressed: _incrementCounter,
              tooltip: 'Increment',
              child: Icon(Icons.add),
            ), // This trailing comma makes auto-formatting nicer for build methods.
          );
        }

        void ambilNilai(SharedPreferences value) {
          setState(() {
             counterx = value.getInt("counter");
          });
        }
}