Flutter后台定位插件background_locator_2的使用

background_locator_2 是一个用于在应用被杀死后仍然能够获取位置更新的Flutter插件。本文将介绍如何安装、配置和使用该插件，并提供完整的示例代码。

安装与设置

安装步骤

1. 在 pubspec.yaml 文件中添加 background_locator_2 依赖：

   dependencies:
     flutter:
       sdk: flutter
     background_locator_2: ^最新版本号
   

2. 运行 flutter pub get 来安装依赖。

设置步骤

请参考 官方Wiki 获取详细的安装和设置说明。

使用方法

以下是一个完整的示例代码，展示了如何使用 background_locator_2 插件来实现后台定位功能。

import 'dart:async';
import 'dart:isolate';
import 'dart:ui';

import 'package:background_locator_2/background_locator.dart';
import 'package:background_locator_2/location_dto.dart';
import 'package:background_locator_2/settings/android_settings.dart';
import 'package:background_locator_2/settings/ios_settings.dart';
import 'package:background_locator_2/settings/locator_settings.dart';
import 'package:flutter/material.dart';
import 'package:location_permissions/location_permissions.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  ReceivePort port = ReceivePort();

  String logStr = '';
  bool isRunning;
  LocationDto lastLocation;

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

    if (IsolateNameServer.lookupPortByName('com.example.background_location') != null) {
      IsolateNameServer.removePortNameMapping('com.example.background_location');
    }

    IsolateNameServer.registerPortWithName(port.sendPort, 'com.example.background_location');

    port.listen(
      (dynamic data) async {
        await updateUI(data);
      },
    );
    initPlatformState();
  }

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

  Future<void> updateUI(dynamic data) async {
    final log = await FileManager.readLogFile();

    LocationDto locationDto = (data != null) ? LocationDto.fromJson(data) : null;
    await _updateNotificationText(locationDto);

    setState(() {
      if (data != null) {
        lastLocation = locationDto;
      }
      logStr = log;
    });
  }

  Future<void> _updateNotificationText(LocationDto data) async {
    if (data == null) {
      return;
    }

    await BackgroundLocator.updateNotificationText(
        title: "New location received",
        msg: "${DateTime.now()}",
        bigMsg: "${data.latitude}, ${data.longitude}");
  }

  Future<void> initPlatformState() async {
    print('Initializing...');
    await BackgroundLocator.initialize();
    logStr = await FileManager.readLogFile();
    print('Initialization done');
    final _isRunning = await BackgroundLocator.isServiceRunning();
    setState(() {
      isRunning = _isRunning;
    });
    print('Running ${isRunning.toString()}');
  }

  @override
  Widget build(BuildContext context) {
    final start = SizedBox(
      width: double.maxFinite,
      child: ElevatedButton(
        child: Text('Start'),
        onPressed: () {
          _onStart();
        },
      ),
    );
    final stop = SizedBox(
      width: double.maxFinite,
      child: ElevatedButton(
        child: Text('Stop'),
        onPressed: () {
          onStop();
        },
      ),
    );
    final clear = SizedBox(
      width: double.maxFinite,
      child: ElevatedButton(
        child: Text('Clear Log'),
        onPressed: () {
          FileManager.clearLogFile();
          setState(() {
            logStr = '';
          });
        },
      ),
    );
    String msgStatus = "-";
    if (isRunning != null) {
      if (isRunning) {
        msgStatus = 'Is running';
      } else {
        msgStatus = 'Is not running';
      }
    }
    final status = Text("Status: $msgStatus");

    final log = Text(
      logStr,
    );

    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Flutter background Locator'),
        ),
        body: Container(
          width: double.maxFinite,
          padding: const EdgeInsets.all(22),
          child: SingleChildScrollView(
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.center,
              children: <Widget>[start, stop, clear, status, log],
            ),
          ),
        ),
      ),
    );
  }

  void onStop() async {
    await BackgroundLocator.unRegisterLocationUpdate();
    final _isRunning = await BackgroundLocator.isServiceRunning();
    setState(() {
      isRunning = _isRunning;
    });
  }

  void _onStart() async {
    if (await _checkLocationPermission()) {
      await _startLocator();
      final _isRunning = await BackgroundLocator.isServiceRunning();

      setState(() {
        isRunning = _isRunning;
        lastLocation = null;
      });
    } else {
      // show error
    }
  }

  Future<bool> _checkLocationPermission() async {
    final access = await LocationPermissions().checkPermissionStatus();
    switch (access) {
      case PermissionStatus.unknown:
      case PermissionStatus.denied:
      case PermissionStatus.restricted:
        final permission = await LocationPermissions().requestPermissions(
          permissionLevel: LocationPermissionLevel.locationAlways,
        );
        if (permission == PermissionStatus.granted) {
          return true;
        } else {
          return false;
        }
        break;
      case PermissionStatus.granted:
        return true;
        break;
      default:
        return false;
        break;
    }
  }

  Future<void> _startLocator() async {
    Map<String, dynamic> data = {'countInit': 1};
    return await BackgroundLocator.registerLocationUpdate(
        LocationCallbackHandler.callback,
        initCallback: LocationCallbackHandler.initCallback,
        initDataCallback: data,
        disposeCallback: LocationCallbackHandler.disposeCallback,
        iosSettings: IOSSettings(
            accuracy: LocationAccuracy.NAVIGATION,
            distanceFilter: 0,
            stopWithTerminate: true),
        autoStop: false,
        androidSettings: AndroidSettings(
            accuracy: LocationAccuracy.NAVIGATION,
            interval: 5,
            distanceFilter: 0,
            client: LocationClient.google,
            androidNotificationSettings: AndroidNotificationSettings(
                notificationChannelName: 'Location tracking',
                notificationTitle: 'Start Location Tracking',
                notificationMsg: 'Track location in background',
                notificationBigMsg:
                    'Background location is on to keep the app up-to-date with your location. This is required for main features to work properly when the app is not running.',
                notificationIconColor: Colors.grey,
                notificationTapCallback:
                    LocationCallbackHandler.notificationCallback)));
  }
}

关键点解释

• 权限管理：确保请求并处理位置权限。
• 后台服务注册：通过 BackgroundLocator.registerLocationUpdate 方法启动后台定位服务。
• 通知更新：使用 BackgroundLocator.updateNotificationText 更新通知内容。

结论

通过上述步骤和示例代码，您可以轻松地在Flutter应用中集成后台定位功能。更多详细信息和高级用法，请参考 官方Wiki。