Flutter：我如何实时收听权限

Question

我正在开发一个应用程序，我想在其中持续侦听位置和电池权限。

示例场景：

1. 用户打开应用
2. 授予权限访问
3. 进入设置并撤销权限
4. 再次打开应用
5. 该应用程序会显示一个快捷栏，通知用户权限已被撤销。

我是初学者，我正在使用flutter-permissions-handler，下面的一段代码显示了我的用法。

    _listenForLocationPermission() {
    Future<PermissionStatus> status = PermissionHandler()
        .checkPermissionStatus(PermissionGroup.locationWhenInUse);
    status.then((PermissionStatus status) {
      setState(() {
        _permissionStatus = status;
        if (_permissionStatus != PermissionStatus.granted) {
          _renderOfflineSnackbar('Offline');
        }
      });
    });
  }

对上述任何建议表示赞赏。

Answer 1

我在同一条船上，发现这有效

您需要使用 WidgetsBindingObserver 扩展您的类

class _AppState extends State<App> with WidgetsBindingObserver {
  PermissionStatus _status;
  ...
  ...

然后将这些方法添加到您的类中

@override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  // check permissions when app is resumed
  // this is when permissions are changed in app settings outside of app
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed) {
      PermissionHandler()
          .checkPermissionStatus(PermissionGroup.locationWhenInUse)
          .then(_updateStatus);
    }
  }

我的完整代码如下，但我没有包含构建小部件以保持简短

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:permission_handler/permission_handler.dart';

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

class App extends StatefulWidget {
  @override
  _AppState createState() => _AppState();
}

class _AppState extends State<App> with WidgetsBindingObserver {
  PermissionStatus _status;

  // check permissions
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
    PermissionHandler() // Check location permission has been granted
        .checkPermissionStatus(PermissionGroup
            .locationWhenInUse) //check permission returns a Future
        .then(_updateStatus); // handling in callback to prevent blocking UI
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  // check permissions when app is resumed
  // this is when permissions are changed in app settings outside of app
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed) {
      PermissionHandler()
          .checkPermissionStatus(PermissionGroup.locationWhenInUse)
          .then(_updateStatus);
    }
  }

override
  Widget build(BuildContext context) {
    return MaterialApp(  
    ...
    ...
}

void _updateStatus(PermissionStatus status) {
    if (status != _status) {
      // check status has changed
      setState(() {
        _status = status; // update
      });
    } else {
      if (status != PermissionStatus.granted) {
        PermissionHandler().requestPermissions(
            [PermissionGroup.locationWhenInUse]).then(_onStatusRequested);
      }
      }
    }
  }

  void _askPermission() {
    PermissionHandler().requestPermissions(
        [PermissionGroup.locationWhenInUse]).then(_onStatusRequested);
  }

  void _onStatusRequested(Map<PermissionGroup, PermissionStatus> statuses) {
    final status = statuses[PermissionGroup.locationWhenInUse];
    if (status != PermissionStatus.granted) {
      // On iOS if "deny" is pressed, open App Settings
      PermissionHandler().openAppSettings();
    } else {
      _updateStatus(status);
    }
  }

我希望这有帮助