我想显示一个simple SnackBar
颤振内部的有状态小部件。我的应用程序创建了新实例MaterialApp
有一个名为的有状态小部件MyHomePage
.
我尝试展示SnackBar in showSnackBar()
方法。但它失败了The method showSnackBar was called on null
.
这段代码有什么问题?
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key}) : super(key: key);
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
@override
void initState() {
super.initState();
showInSnackBar("Some text");
}
@override
Widget build(BuildContext context) {
return new Padding(
key: _scaffoldKey,
padding: const EdgeInsets.all(16.0),
child: new Text("Simple Text")
);
}
void showInSnackBar(String value) {
_scaffoldKey.currentState.showSnackBar(new SnackBar(
content: new Text(value)
));
}
}
解决方案:
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new Scaffold(body: new MyHomePage()),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key}) : super(key: key);
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
@override
void initState() {
super.initState();
}
@override
Widget build(BuildContext context) {
showInSnackBar("Some text");
return new Padding(
padding: const EdgeInsets.all(16.0),
child: new Scaffold(
body: new Text("Simple Text")
)
);
}
void showInSnackBar(String value) {
Scaffold.of(context).showSnackBar(new SnackBar(
content: new Text(value)
));
}
}
就我而言,我有这样的代码(在类状态)
final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
void showInSnackBar(String value) {
_scaffoldKey.currentState.showSnackBar(new SnackBar(content: new Text(value)));
}
但我没有设置脚手架的钥匙。
所以当我添加键:_scaffoldKey
@override
Widget build(BuildContext context) {
return new Scaffold(
key: _scaffoldKey,
body: new SafeArea(
小吃店开始工作:)
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