Flutter 如何获取页面未被处理_Flutter

Flutter 如何获取页面未被处理

flutter

Flutter 如何获取页面未被处理,flutter,Flutter,我有一个应用程序，它有使用位置的mappage class _MapPageState extends State<MapPage> { LocationData currentLocation; Location _locationService = new Location(); @override void initState(){ super.initState();

我有一个应用程序，它有使用位置的mappage

class _MapPageState extends State<MapPage> {
  LocationData currentLocation;  
  Location _locationService = new Location();   
  @override
  void initState(){
    super.initState();                                                
    _locationService.onLocationChanged().listen((LocationData result) async { 
      setState(() {       
        print(result.latitude);
        print(result.longitude);                                                  
        currentLocation = result;                                             
      });                                                                     
    });  
  }

所以，我有两个想法

释放页面时，删除

onLocationChanged（）

侦听器

检查在

setState（）之前是否已释放状态


如何解决此问题？？？
您可以复制粘贴下面的两个文件，并直接替换官方示例的代码



在导航到ListenLocationWidget页面后，
您可以在dispose（）


代码片段
class _MyHomePageState
...
   RaisedButton(
      child: Text('Open route'),
      onPressed: () {
        Navigator.push(
          context,
          MaterialPageRoute<void>(
              builder: (context) => ListenLocationWidget()),
        );
      },
    ),
    PermissionStatusWidget(),
    Divider(height: 32),
    ServiceEnabledWidget(),
    Divider(height: 32),
    GetLocationWidget(),
    Divider(height: 32),
    //ListenLocationWidget()


class _ListenLocationState extends State<ListenLocationWidget> {
...
StreamSubscription<LocationData> _locationSubscription;
  String _error;

  @override
  void initState() {
    print("initState");
    super.initState();
    _listenLocation();
  }

  @override
  void dispose() {
    print("stopListen");
    _stopListen();
    super.dispose();
  }
  
  Future<void> _listenLocation() async {
    _locationSubscription =
        location.onLocationChanged.handleError((dynamic err) {
      setState(() {
        _error = err.code;
      });
      _locationSubscription.cancel();
    }).listen((LocationData currentLocation) {
      setState(() {
        print("setState");
        _error = null;

        _location = currentLocation;
      });
    });
  }

  Future<void> _stopListen() async {
    _locationSubscription.cancel();
  }

完整代码main.dart

import 'package:flutter/material.dart';
import 'package:location/location.dart';
import 'package:url_launcher/url_launcher.dart';

import 'get_location.dart';
import 'listen_location.dart';
import 'permission_status.dart';
import 'service_enabled.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Location',
      theme: ThemeData(
        primarySwatch: Colors.amber,
      ),
      home: const MyHomePage(title: 'Flutter Location Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  final Location location = Location();

  Future<void> _showInfoDialog() {
    return showDialog<void>(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          title: const Text('Demo Application'),
          content: SingleChildScrollView(
            child: ListBody(
              children: <Widget>[
                const Text('Created by Guillaume Bernos'),
                InkWell(
                  child: Text(
                    'https://github.com/Lyokone/flutterlocation',
                    style: TextStyle(
                      decoration: TextDecoration.underline,
                    ),
                  ),
                  onTap: () =>
                      launch('https://github.com/Lyokone/flutterlocation'),
                ),
              ],
            ),
          ),
          actions: <Widget>[
            FlatButton(
              child: const Text('Ok'),
              onPressed: () {
                Navigator.of(context).pop();
              },
            ),
          ],
        );
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        actions: <Widget>[
          IconButton(
            icon: Icon(Icons.info_outline),
            onPressed: _showInfoDialog,
          )
        ],
      ),
      body: Container(
        padding: const EdgeInsets.all(32),
        child: Column(
          children: <Widget>[
            RaisedButton(
              child: Text('Open route'),
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute<void>(
                      builder: (context) => ListenLocationWidget()),
                );
              },
            ),
            PermissionStatusWidget(),
            Divider(height: 32),
            ServiceEnabledWidget(),
            Divider(height: 32),
            GetLocationWidget(),
            Divider(height: 32),
            //ListenLocationWidget()
          ],
        ),
      ),
    );
  }
}

导入“包装：颤振/材料.省道”；
导入“package:location/location.dart”；
导入“package:url_launcher/url_launcher.dart”；
导入“get_location.dart”；
导入“listen_location.dart”；
导入“permission_status.dart”；
导入'service_enabled.dart'；
void main（）=>runApp（MyApp（））；
类MyApp扩展了无状态小部件{
//此小部件是应用程序的根。
@凌驾
小部件构建（构建上下文）{
返回材料PP(
标题：“颤振位置”，
主题：主题数据(
主样本：颜色。琥珀色，
),
主页：const MyHomePage（标题：“颤振位置演示”），
);
}
}
类MyHomePage扩展StatefulWidget{
constMyHomepage（{Key，this.title}）：super（Key:Key）；
最后的字符串标题；
@凌驾
_MyHomePageState createState（）=>\u MyHomePageState（）；
}
类_MyHomePageState扩展状态{
最终位置=位置（）；
未来(showInfoDialog){
返回显示对话框(
上下文：上下文，
生成器：（BuildContext上下文）{
返回警报对话框(
标题：常量文本（“演示应用程序”），
内容：SingleChildScrollView(
子：列表体(
儿童：[
常量文本（“由Guillaume Bernos创建”），
墨水池(
子：文本(
'https://github.com/Lyokone/flutterlocation',
样式：TextStyle(
装饰：textEdition.underline，
),
),
onTap:（）=>
发射（'https://github.com/Lyokone/flutterlocation'),
),
],
),
),
行动：[
扁平按钮(
子项：常量文本（'Ok'），
已按下：（）{
Navigator.of（context.pop（）；
},
),
],
);
},
);
}
@凌驾
小部件构建（构建上下文）{
返回脚手架(
appBar:appBar(
标题：文本（widget.title），
行动：[
图标按钮(
图标：图标（Icons.info\u轮廓），
按下按钮：\u showInfoDialog，
)
],
),
主体：容器(
填充：常量边集。全部（32），
子：列(
儿童：[
升起的按钮(
子项：文本（“开放路线”），
已按下：（）{
导航器。推(
上下文
材料路线(
生成器：（上下文）=>ListenLocationWidget（）），
);
},
),
PermissionStatusWidget（），
分隔器（高度：32），
ServiceEnabledWidget（），
分隔器（高度：32），
GetLocationWidget（），
分隔器（高度：32），
//ListenLocationWidget（）
],
),
),
);
}
}
这是否回答了您的问题？非常感谢你。我测试了工作演示。我从对您的代码进行大引用开始。
import 'dart:async';

import 'package:flutter/material.dart';
import 'package:location/location.dart';

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

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

class _ListenLocationState extends State<ListenLocationWidget> {
  final Location location = Location();

  LocationData _location;
  StreamSubscription<LocationData> _locationSubscription;
  String _error;

  @override
  void initState() {
    print("initState");
    super.initState();
    _listenLocation();
  }

  @override
  void dispose() {
    print("stopListen");
    _stopListen();
    super.dispose();
  }
  
  Future<void> _listenLocation() async {
    _locationSubscription =
        location.onLocationChanged.handleError((dynamic err) {
      setState(() {
        _error = err.code;
      });
      _locationSubscription.cancel();
    }).listen((LocationData currentLocation) {
      setState(() {
        print("setState");
        _error = null;

        _location = currentLocation;
      });
    });
  }

  Future<void> _stopListen() async {
    _locationSubscription.cancel();
  }

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Container(
        color: Colors.white,
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            Text(
              'Listen location: ' + (_error ?? '${_location ?? "unknown"}'),
              style: Theme.of(context).textTheme.body2,
            ),
            Row(
              children: <Widget>[
                Container(
                  margin: const EdgeInsets.only(right: 42),
                  child: RaisedButton(
                    child: const Text('Listen'),
                    onPressed: _listenLocation,
                  ),
                ),
                RaisedButton(
                  child: const Text('Stop'),
                  onPressed: _stopListen,
                )
              ],
            ),
          ],
        ),
      ),
    );
  }
}

import 'package:flutter/material.dart';
import 'package:location/location.dart';
import 'package:url_launcher/url_launcher.dart';

import 'get_location.dart';
import 'listen_location.dart';
import 'permission_status.dart';
import 'service_enabled.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Location',
      theme: ThemeData(
        primarySwatch: Colors.amber,
      ),
      home: const MyHomePage(title: 'Flutter Location Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  final Location location = Location();

  Future<void> _showInfoDialog() {
    return showDialog<void>(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          title: const Text('Demo Application'),
          content: SingleChildScrollView(
            child: ListBody(
              children: <Widget>[
                const Text('Created by Guillaume Bernos'),
                InkWell(
                  child: Text(
                    'https://github.com/Lyokone/flutterlocation',
                    style: TextStyle(
                      decoration: TextDecoration.underline,
                    ),
                  ),
                  onTap: () =>
                      launch('https://github.com/Lyokone/flutterlocation'),
                ),
              ],
            ),
          ),
          actions: <Widget>[
            FlatButton(
              child: const Text('Ok'),
              onPressed: () {
                Navigator.of(context).pop();
              },
            ),
          ],
        );
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        actions: <Widget>[
          IconButton(
            icon: Icon(Icons.info_outline),
            onPressed: _showInfoDialog,
          )
        ],
      ),
      body: Container(
        padding: const EdgeInsets.all(32),
        child: Column(
          children: <Widget>[
            RaisedButton(
              child: Text('Open route'),
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute<void>(
                      builder: (context) => ListenLocationWidget()),
                );
              },
            ),
            PermissionStatusWidget(),
            Divider(height: 32),
            ServiceEnabledWidget(),
            Divider(height: 32),
            GetLocationWidget(),
            Divider(height: 32),
            //ListenLocationWidget()
          ],
        ),
      ),
    );
  }
}