Flutter:我如何实时收听权限 [英] Flutter: How do I listen to permissions real time

问题描述

我正在开发一个应用程序，我想在其中持续监听位置和电池权限.

I am working on an app in which I want to continuously listen to location and battery permissions.

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. 该应用会显示一个 snackbar，通知用户权限已被撤销.

1. The user opens the app
2. Grants permission access
3. Goes to settings and revokes the permissions
4. Opens the app again
5. The app displays a snackbar that informs the user that permission has been revoked.

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

I am a beginner and I am using the flutter-permissions-handler and the piece of code below shows my usage.

    _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.

Any advice on the above is appreciated.

推荐答案

我在同一条船上，发现这有效

I'm in the same boat and have found that this works

您需要使用 WidgetsBindingObserver 扩展您的类

You need to extend your class with WidgetsBindingObserver

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

然后将这些方法添加到您的类中

then add these methods to your class

@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，但为了保持简短，我没有包含构建小部件

My full code is below, but I've not included the build widget to keep it brief

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);
    }
  }

希望能帮到你

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