flutter/examples/platform_services/lib/main.dart

// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';

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

class PlatformServices extends StatefulWidget {
  @override
  _PlatformServicesState createState() => new _PlatformServicesState();
}

class _PlatformServicesState extends State<PlatformServices> {
  double _latitude;
  double _longitude;

  @override
  Widget build(BuildContext context) {
    return new Material(
      child: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: <Widget>[
            new Text('Hello from Flutter!'),
            new RaisedButton(
              child: new Text('Get Location'),
              onPressed: _getLocation
            ),
            new Text('Latitude: $_latitude, Longitude: $_longitude'),
          ]
        )
      )
    );
  }

  Future<Null> _getLocation() async {
    final Map<String, String> message = <String, String>{'provider': 'network'};
    final Map<String, dynamic> reply = await PlatformMessages.sendJSON('getLocation', message);
    // If the widget was removed from the tree while the message was in flight,
    // we want to discard the reply rather than calling setState to update our
    // non-existent appearance.
    if (!mounted)
      return;
    setState(() {
      _latitude = reply['latitude'].toDouble();
      _longitude = reply['longitude'].toDouble();
    });
  }
}

void main() {
  runApp(new PlatformServices());
}