使用不包含脚手架的上下文调用Scaffold.of()

如你所见，我的按钮在刑台的身体里。但是我得到了这个异常:

使用不包含脚手架的上下文调用Scaffold.of()。

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('SnackBar Playground'),
      ),
      body: Center(
        child: RaisedButton(
          color: Colors.pink,
          textColor: Colors.white,
          onPressed: _displaySnackBar(context),
          child: Text('Display SnackBar'),
        ),
      ),
    );
  }
}

_displaySnackBar(BuildContext context) {
  final snackBar = SnackBar(content: Text('Are you talkin\' to me?'));
  Scaffold.of(context).showSnackBar(snackBar);
}

编辑:

我找到了这个问题的另一个解决方案。如果我们给Scaffold一个键GlobalKey<ScaffoldState>，我们就可以像下面那样显示SnackBar，而不需要在Builder小部件中包装我们的主体。返回脚手架的小部件应该是一个有状态的小部件。

 _scaffoldKey.currentState.showSnackBar(snackbar);

当前回答

一个更有效的解决方案是将构建功能拆分为几个小部件。这将引入一个“新上下文”，从中您可以获得Scaffold

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Scaffold.of example.')),
        body: MyScaffoldBody(),
      ),
    );
  }
}

class MyScaffoldBody extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: RaisedButton(
          child: Text('Show a snackBar'),
          onPressed: () {
            Scaffold.of(context).showSnackBar(
              SnackBar(
                content: Text('Have a Snack'),
              ),
            );
          }),
    );
  }
}

2020-04-17 19:42:00

其他回答

也许这段代码里有解决方案。

ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text("SnackBar Message")));

2021-05-02 17:09:56

在这里，我们使用一个构建器来封装另一个需要小吃店的小部件

Builder(builder: (context) => GestureDetector(
    onTap: () {
        Scaffold.of(context).showSnackBar(SnackBar(
            content: Text('Your Services have been successfully created Snackbar'),
        ));
        
    },
    child: Container(...)))

2020-07-07 03:11:43

你可以用两种方法来解决这个问题:

1)使用Builder小部件

Scaffold(
    appBar: AppBar(
        title: Text('My Profile'),
    ),
    body: Builder(
        builder: (ctx) => RaisedButton(
            textColor: Colors.red,
            child: Text('Submit'),
            onPressed: () {
                 Scaffold.of(ctx).showSnackBar(SnackBar(content: Text('Profile Save'),),);
            }               
        ),
    ),
);

2)使用GlobalKey

class HomePage extends StatelessWidget {
  
  final globalKey = GlobalKey<ScaffoldState>();
  
  @override
  Widget build(BuildContext context) {
     return Scaffold(
       key: globalKey,
       appBar: AppBar(
          title: Text('My Profile'),
       ),
       body:  RaisedButton(
          textColor: Colors.red,
          child: Text('Submit'),
          onPressed: (){
               final snackBar = SnackBar(content: Text('Profile saved'));
               globalKey.currentState.showSnackBar(snackBar);
          },
        ),
     );
   }
}

2019-10-10 07:35:53

从Flutter版本1.23-18.1。你可以使用脚手架信使

final mainScaffoldMessengerKey = GlobalKey<ScaffoldMessengerState>();

class Main extends StatelessWidget {
  @override
  Widget build(BuildContext) {
    return MaterialApp(
      ...
      scaffoldMessengerKey: mainScaffoldMessengerKey
      ...
    );
  }
}

app内部某处:

mainScaffoldMessengerKey.currentState.showSnackBar(Snackbar(...));

2020-10-27 15:03:11

           Expanded(
              child: Container(
                width: MediaQuery.of(context).size.width,
                height: MediaQuery.of(context).size.height,
                child: Builder(
                  builder: (context) => RaisedButton(
                    onPressed: () {
                        final snackBar = SnackBar(
                          content: Text("added to cart"),
                           action: SnackBarAction(
                            label: 'Undo',
                             onPressed: () {
                              // Some code to undo the change.
                            },
                          ),
                        );
                    },
                    textColor: Colors.white,
                    color: Colors.pinkAccent,
                    child: Text("Add To Cart",
                        style: TextStyle(
                            fontSize: 18, fontWeight: FontWeight.w600)),
                  ),
                ),
              ),
            )

2021-02-05 10:48:45

使用不包含脚手架的上下文调用Scaffold.of()

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