在颤动中跟踪背景位置时使用 background_locator 插件时出现问题答案

【问题标题】：Issue while using background_locator plugin while tracking background location in flutter在颤动中跟踪背景位置时使用 background_locator 插件时出现问题
【发布时间】：2022-08-04 19:13:04
【问题描述】：

我正在尝试使用颤振在后台跟踪位置，为此我正在使用background_locator 插件。它的实现方式是注册了某些静态回调函数。我已经声明了一个文件类型的类变量来在后台保存日志。全局变量是在类的最开始构建的。

问题：调用回调方法时，构建的全局变量变为空。因此，尽管我可以在控制台中看到位置日志，但由于对象为空，我无法将其写入文件。

尝试：

我已尝试使用他们文档中提供的确切示例。
我已将其声明为非静态属性并尝试使用类对象进行访问。
尝试将其声明为静态属性。

每次需要时都尝试使用相同的路径构建文件对象，但会引发以下问题。

在通道 plugins.flutter.io/path_provider 上找不到方法 getApplicationDocumentsDirectory 的实现

这是我的完整源代码供参考。

import \'dart:async\';
import \'dart:ffi\';
import \'dart:io\';
import \'dart:isolate\';
import \'dart:math\';
import \'dart:ui\';

import \'package:background_locator/background_locator.dart\';
import \'package:background_locator/location_dto.dart\';
import \'package:background_locator/settings/android_settings.dart\';
import \'package:background_locator/settings/ios_settings.dart\';
import \'package:background_locator/settings/locator_settings.dart\';
import \'package:flutter/material.dart\';
import \'package:location_permissions/location_permissions.dart\';
import \'package:path_provider/path_provider.dart\';
import \'package:permission_handler/permission_handler.dart\' as ph;

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

class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  _MyAppState createState() => _MyAppState();
}

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

  String logStr = \'\';
  bool isRunning = false;
  LocationDto? lastLocation;

  bool permissionsGranted = false;

  static const String isolateName = \'LocatorIsolate\';

  static int _count = -1;

  static File? finalFile;

  void requestPermission() async {
    var storageStatus = await ph.Permission.storage.status;

    if (!storageStatus.isGranted) {
      await ph.Permission.storage.request();
    }

    if (storageStatus.isGranted) {
      permissionsGranted = true;
      setPrerequisites();
    }

    setState(() {});
  }

  static Future<void> init(Map<dynamic, dynamic> params) async {
    //TODO change logs
    print(\"***********Init callback handler\");
    if (params.containsKey(\'countInit\')) {
      dynamic tmpCount = params[\'countInit\'];
      if (tmpCount is double) {
        _count = tmpCount.toInt();
      } else if (tmpCount is String) {
        _count = int.parse(tmpCount);
      } else if (tmpCount is int) {
        _count = tmpCount;
      } else {
        _count = -2;
      }
    } else {
      _count = 0;
    }
    print(\"$_count\");
    await setLogLabel(\"start\");
    final SendPort? send = IsolateNameServer.lookupPortByName(isolateName);
    send?.send(null);
  }

  static Future<void> disposeLocationService() async {
    await setLogLabel(\"end\");
    final SendPort? send = IsolateNameServer.lookupPortByName(isolateName);
    send?.send(null);
  }

  static Future<void> callback(LocationDto locationDto) async {
    await setLogPosition(_count, locationDto);
    final SendPort? send = IsolateNameServer.lookupPortByName(isolateName);
    send?.send(locationDto);
    _count++;
  }

  static Future<void> setLogLabel(String label) async {
    final date = DateTime.now();
    await _MyAppState().writeToLogFile(
        \'------------\\n$label: ${formatDateLog(date)}\\n------------\\n\');
  }

  static Future<void> setLogPosition(int count, LocationDto data) async {
    final date = DateTime.now();
    await _MyAppState().writeToLogFile(
        \'$count : ${formatDateLog(date)} --> ${formatLog(data)} --- isMocked: ${data.isMocked}\\n\');
  }

  static double dp(double val, int places) {
    num mod = pow(10.0, places);
    return ((val * mod).round().toDouble() / mod);
  }

  static String formatDateLog(DateTime date) {
    return date.hour.toString() +
        \":\" +
        date.minute.toString() +
        \":\" +
        date.second.toString();
  }

  static String formatLog(LocationDto locationDto) {
    return dp(locationDto.latitude, 4).toString() +
        \" \" +
        dp(locationDto.longitude, 4).toString();
  }

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

    if (permissionsGranted) {
      setPrerequisites();
    } else {
      requestPermission();
    }
  }

  void setPrerequisites() async {
    finalFile = await _getTempLogFile();

    if (IsolateNameServer.lookupPortByName(isolateName) != null) {
      IsolateNameServer.removePortNameMapping(isolateName);
    }

    IsolateNameServer.registerPortWithName(port.sendPort, isolateName);

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

    setState(() {});
  }

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

    await _updateNotificationText(data);

    setState(() {
      if (data != null) {
        lastLocation = data;
      }
      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 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: const 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: () {
          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
    }
  }

  static Future<void> initCallback(Map<dynamic, dynamic> params) async {
    await init(params);
  }

  static Future<void> disposeCallback() async {
    await disposeLocationService();
  }

  Future<void> locationServicecallback(LocationDto locationDto) async {
    await callback(locationDto);
  }

  static Future<void> notificationCallback() async {
    print(\'***notificationCallback\');
  }

  Future<void> writeToLogFile(String log) async {
    await finalFile!.writeAsString(log, mode: FileMode.append);
  }

  Future<String> readLogFile() async {
    return finalFile!.readAsString();
  }

  static Future<File?> _getTempLogFile() async {
    File file =
        File(\'${(await getApplicationDocumentsDirectory()).path}/log.txt\');

    if (file.existsSync()) {
      return file;
    } else {
      file = await file.create(recursive: true);
    }
    return file;
  }

  Future<void> clearLogFile() async {
    await finalFile!.writeAsString(\'\');
  }

  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;
        }
      case PermissionStatus.granted:
        return true;
      default:
        return false;
    }
  }

  Future<void> _startLocator() async {
    Map<String, dynamic> data = {\'countInit\': 1};
    return await BackgroundLocator.registerLocationUpdate(
      callback,
      initCallback: initCallback,
      initDataCallback: data,
      disposeCallback: disposeCallback,
      iosSettings: const IOSSettings(
          accuracy: LocationAccuracy.NAVIGATION, distanceFilter: 0),
      autoStop: false,
      androidSettings: const 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-tp-date with your location. This is required for main features to work properly when the app is not running.\',
          notificationIconColor: Colors.grey,
          notificationTapCallback: notificationCallback,
        ),
      ),
    );
  }
}

任何帮助/建议将不胜感激。谢谢！

为同样的问题而苦苦挣扎。在回调函数中没有得到回调。背景位置的任何解决方法都会颤抖吗？

标签： android ios flutter dart background

【解决方案1】：

回调函数没有被调用是我在 1.6.12 版本中遇到的问题。

我解决了这个问题

在 github 上分叉 background_locator 存储库。
将 repo 克隆到我的计算机
打开 location_dto.dart 文件并转到fromJson 函数。
添加了 json[Keys.ARG_PROVIDER] ?? '' 反而
提交并推送到我的分叉存储库
在 pubspec.yaml 中，我更新了我的依赖项以指向我的分叉存储库，如下所示：
```
  background_locator:
    git:
      url: git@github.com:frankvollebregt/background_locator.git
```
如果您发现任何问题，请关注这两个 github 问题：
- https://github.com/rekabhq/background_locator/issues/320
- https://github.com/rekabhq/background_locator/issues/301

【讨论】：

感谢 Oumar 的回复。但是我仍然无法执行从您的分支签出的示例。我一直面临的问题是日志没有正确写入文件。每次尝试创建日志文件时，都会引发问题。如果你有你的 git，你能分享一下这个工作示例吗？！

【解决方案2】：

background_locator 在最新的 Flutter sdk 版本上不起作用对我来说，当我执行这些步骤时它起作用了

Flutter sdk 版本应该是：3.0.1
在 pubspec.yaml 文件中更改 sdk：">=2.8.0 <3.0.0"
不要将代码迁移到空安全
在 gradle-wrapper.properties 中将 gradle 版本更改为 gradle-6.5
android/build gradle 将 ext.kotlin_version 更改为 '1.4.31'
android/app/build gradle 将 compileSdkVersion 更改为 31，将 minSdkVersion 更改为 19，将 targetSdkVersion 更改为 30

【讨论】：