Question

昨天我开始使用Flutter，因为它看起来很神奇。但现在我有一个例外，让我难过。当我点击抽屉中的项目时，我希望抽屉关闭。但是当我点击它们时，我得到一个例外。下面是我的代码和例外。我希望有人可以帮我解决这个问题并向我解释为什么它不能进一步扩展我对框架的了解。

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
        Column buildButtonColumn(IconData icon, String label) {
            Color color = Theme.of(context).primaryColor;

            return new Column(
                mainAxisSize: MainAxisSize.min,
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                    new Icon(icon, color: color),
                    new Container(
                        margin: const EdgeInsets.only(top: 8.0),
                        child: new Text(
                            label,
                            style: new TextStyle(
                                fontSize: 12.0,
                                fontWeight: FontWeight.w400,
                                color: color,
                            ),
                        ),
                    ),
                ],
            );
        }
        Widget titleSection = new Container(
            padding: const EdgeInsets.all(32.0),
            child: new Row(
                children: [
                    new Expanded(
                        child: new Column(
                            crossAxisAlignment: CrossAxisAlignment.start,
                            children: [
                                new Container(
                                    padding: const EdgeInsets.only(bottom: 8.0),
                                    child: new Text(
                                        'Oeschinen Lake Campground',
                                        style: new TextStyle(
                                            fontWeight: FontWeight.bold
                                        ),
                                    ),
                                ),
                                new Text(
                                    'Kandersteg, Switzerland',
                                    style: new TextStyle(
                                        color: Colors.grey[500],
                                    ),
                                ),
                            ],
                        ),
                    ),
                    new Icon(
                        Icons.star,
                        color: Colors.red[500],
                    ),
                    new Text('41'),
                ],
            ),
        );
        Widget buttonSection = new Container(
            child: new Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: [
                    buildButtonColumn(Icons.call, 'CALL'),
                    buildButtonColumn(Icons.near_me, 'ROUTE'),
                    buildButtonColumn(Icons.share, 'SHARE'),
                ],
            ),
        );
        Widget textSection = new Container(
            padding: const EdgeInsets.all(32.0),
            child: new Text(
                'Lake Oeschinen lies at the foot of the Blüemlisalp in the Bernese Alps. Situated 1,578 meters above sea level, it is one of the larger Alpine Lakes. A gondola ride from Kandersteg, followed by a half-hour walk through pastures and pine forest, leads you to the lake, which warms to 20 degrees Celsius in the summer. Activities enjoyed here include rowing, and riding the summer toboggan run.',
                softWrap: true,
            ),
        );

        Widget drawer = new Drawer(
            child: new ListView(
                padding: EdgeInsets.zero,
                children: <Widget>[
                    new DrawerHeader(
                        child: new Text('Drawer Header'),
                        decoration: new BoxDecoration(
                            color: Colors.blue,
                        ),
                    ),
                    new ListTile(
                        title: new Text('Item 1'),
                        onTap: () {
                            Navigator.pop(context);
                        },
                    ),
                    new ListTile(
                        title: new Text('Item 2'),
                        onTap: () {
                            Navigator.pop(context);
                        },
                    ),
                ],
            ),
        );

        return new MaterialApp(
            title: 'Flutter Demo',
            theme: new ThemeData(
                primarySwatch: Colors.red,
            ),
            home: new Scaffold(
                appBar: new AppBar(
                    title: new Text('Top Lakes'),
                ),
                drawer: drawer,
                body: new ListView(
                    children: [
                        new Image.asset(
                            'images/lake.jpg',
                            height: 240.0,
                            fit: BoxFit.cover,
                        ),
                        titleSection,
                        buttonSection,
                        textSection,
                    ],
                ),
            ),
        );
    }
}

I/flutter (12997): ══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
I/flutter (12997): The following assertion was thrown while handling a gesture:
I/flutter (12997): Navigator operation requested with a context that does not include a Navigator.
I/flutter (12997): The context used to push or pop routes from the Navigator must be that of a widget that is a
I/flutter (12997): descendant of a Navigator widget.

Answer 1

在Flutter中，路由由Navigator小部件管理。虽然您可以直接创建导航器，但通常以root身份使用MaterialApp或WidgetApp。

尝试使用WidgetApp扩展MyApp或使用MyApp root包装MaterialApp。

示例：

void main() =>  runApp(new MaterialApp(home: new MyApp(),));

Answer 2

答案比这更简单：您需要为要从中调用上下文的任何窗口小部件分配密钥

所以不要打电话：

Scaffold.of(context).showSnack....

你应该打电话：

scaffoldKey.currentState.showSnack...

为此，您可以创建脚手架键，如：

final GlobalKey<ScaffoldState> scaffoldKey = new GlobalKey<ScaffoldState>();

然后将该密钥分配给您的脚手架，如：

Widget build(BuildContext context) { return new Scaffold( key: scaffoldKey,

抽屉上的Navigator.pop（上下文）异常

2 个答案: