import 'package:flutter/material.dart';
main() {
runApp(MaterialApp(
home: HomeScreen(),
));
}
class HomeScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text('Rite.ly'),
),
body: new Container(
decoration: new BoxDecoration(
image: new DecorationImage(
image: new AssetImage('assets/login_background.png'),
fit: BoxFit.fill,
)),
child: new ListView(
children: [
new Padding(
padding:
const EdgeInsets.only(top: 16.0, bottom: 8.0, left: 16.0),
child: new Text('Link : ',
style: new TextStyle(color: Colors.white)),
),
_takeUrl(context),
],
)),
);
}
}
Widget _takeUrl(BuildContext context) {
return new Container(
margin: new EdgeInsets.symmetric(horizontal: 20.0),
decoration: new BoxDecoration(
color: Colors.white, borderRadius: new BorderRadius.circular(12.0)),
child: new Row(
mainAxisAlignment: MainAxisAlignment.start,
children: [
new Expanded(
child: new Column(
children: [
new TextField(
decoration: new InputDecoration(
contentPadding: const EdgeInsets.all(16.0),
hintText: 'Link to be Shortened'),
),
],
),
),
new IconButton(
icon: new Icon(
Icons.content_paste,
color: Color.fromARGB(255, 191, 53, 146),
),
onPressed: () {
Scaffold.of(context).showSnackBar(new SnackBar(
content: new Text('Hello!'),
));
},
)
],
));
}
在上面的代码中,将上下文传递给与构建方法分离的片段,在调用Scaffold.of时会出现错误:
I/flutter (20313): Another exception was thrown: Scaffold.of() called with a context that does not contain a Scaffold.
但是,当我们使用Builder小部件并将_takeURL作为构建器传递给Builder时,这会得到解决。之后Snack Bar完美无缺。
什么可能是负责任的?我需要阅读什么来理解原因?
class HomeScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text('Rite.ly'),
),
body: new Container(
decoration: new BoxDecoration(
image: new DecorationImage(
image: new AssetImage('assets/login_background.png'),
fit: BoxFit.fill,
)),
child: new ListView(
children: [
new Padding(
padding:
const EdgeInsets.only(top: 16.0, bottom: 8.0, left: 16.0),
child: new Text('Link : ',
style: new TextStyle(color: Colors.white)),
),
Builder(builder: _takeUrl,),
],
)),
);
}
}
传递的背景不是Scaffold.of(context)
所需要的。您需要将它包装在Builder中,因为Flutter BuildContext指定:
Widget _takeUrl(BuildContext context) {
return Builder(builder: (BuildContext context) {
return new Container(
margin: new EdgeInsets.symmetric(horizontal: 20.0),
decoration: new BoxDecoration(
color: Colors.white, borderRadius: new BorderRadius.circular(12.0)),
child: new Row(
mainAxisAlignment: MainAxisAlignment.start,
children: [
new Expanded(
child: new Column(
children: [
new TextField(
decoration: new InputDecoration(
contentPadding: const EdgeInsets.all(16.0),
hintText: 'Link to be Shortened'),
),
],
),
),
new IconButton(
icon: new Icon(
Icons.content_paste,
color: Color.fromARGB(255, 191, 53, 146),
),
onPressed: () {
Scaffold.of(context).showSnackBar(new SnackBar(
content: new Text('Hello!'),
));
},
)
],
));
});
}