flutter/examples/platform_channel/lib/main.dart

// Copyright 2014 The Flutter 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 PlatformChannel extends StatefulWidget {
  const PlatformChannel({super.key});

  @override
  State<PlatformChannel> createState() => _PlatformChannelState();
}

class _PlatformChannelState extends State<PlatformChannel> {
  static const MethodChannel methodChannel = MethodChannel('samples.flutter.io/battery');
  static const EventChannel eventChannel = EventChannel('samples.flutter.io/charging');

  String _batteryLevel = 'Battery level: unknown.';
  String _chargingStatus = 'Battery status: unknown.';

  Future<void> _getBatteryLevel() async {
    String batteryLevel;
    try {
      final int? result = await methodChannel.invokeMethod('getBatteryLevel');
      batteryLevel = 'Battery level: $result%.';
    } on PlatformException catch (e) {
      if (e.code == 'NO_BATTERY') {
        batteryLevel = 'No battery.';
      } else {
        batteryLevel = 'Failed to get battery level.';
      }
    }
    setState(() {
      _batteryLevel = batteryLevel;
    });
  }

  @override
  void initState() {
    super.initState();
    eventChannel.receiveBroadcastStream().listen(_onEvent, onError: _onError);
  }

  void _onEvent(Object? event) {
    setState(() {
      _chargingStatus = "Battery status: ${event == 'charging' ? '' : 'dis'}charging.";
    });
  }

  void _onError(Object error) {
    setState(() {
      _chargingStatus = 'Battery status: unknown.';
    });
  }

  @override
  Widget build(BuildContext context) {
    return Material(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: <Widget>[
          Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(_batteryLevel, key: const Key('Battery level label')),
              Padding(
                padding: const EdgeInsets.all(16.0),
                child: ElevatedButton(onPressed: _getBatteryLevel, child: const Text('Refresh')),
              ),
            ],
          ),
          Text(_chargingStatus),
        ],
      ),
    );
  }
}

void main() {
  runApp(const MaterialApp(home: PlatformChannel()));
}