找不到物质小部件

我是新的扑动和我正在尝试执行的例子给你。我只想使用 TextField 小部件获取一些用户输入。问题是我得到了一个“没有物质部件找到”错误。我做错了什么？谢谢你。

密码:

import 'package:flutter/material.dart';


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




class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
home: new ExampleWidget(),
);
}
}




/// Opens an [AlertDialog] showing what the user typed.
class ExampleWidget extends StatefulWidget {
ExampleWidget({Key key}) : super(key: key);


@override
_ExampleWidgetState createState() => new _ExampleWidgetState();
}


/// State for [ExampleWidget] widgets.
class _ExampleWidgetState extends State<ExampleWidget> {
final TextEditingController _controller = new TextEditingController();


@override
Widget build(BuildContext context) {
return new Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new TextField(
controller: _controller,
decoration: new InputDecoration(
hintText: 'Type something',
),
),
new RaisedButton(
onPressed: () {
showDialog(
context: context,
child: new AlertDialog(
title: new Text('What you typed'),
content: new Text(_controller.text),
),
);
},
child: new Text('DONE'),
),
],
);
}
}

这是错误堆栈:

Launching lib/main.dart on Android SDK built for x86 in debug mode...
Built build/app/outputs/apk/app-debug.apk (21.5MB).
I/flutter ( 5187): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 5187): The following assertion was thrown building InputDecorator(decoration: InputDecoration(hintText:
I/flutter ( 5187): "Type something"); baseStyle: null; isFocused: false; isEmpty: true; dirty):
I/flutter ( 5187): No Material widget found.
I/flutter ( 5187): InputDecorator widgets require a Material widget ancestor.
I/flutter ( 5187): In material design, most widgets are conceptually "printed" on a sheet of material. In Flutter's
I/flutter ( 5187): material library, that material is represented by the Material widget. It is the Material widget
I/flutter ( 5187): that renders ink splashes, for instance. Because of this, many material library widgets require that
I/flutter ( 5187): there be a Material widget in the tree above them.
I/flutter ( 5187): To introduce a Material widget, you can either directly include one, or use a widget that contains
I/flutter ( 5187): Material itself, such as a Card, Dialog, Drawer, or Scaffold.
I/flutter ( 5187): The specific widget that could not find a Material ancestor was:
I/flutter ( 5187):   InputDecorator(decoration: InputDecoration(hintText: "Type something"); baseStyle: null;
I/flutter ( 5187):   isFocused: false; isEmpty: true)
I/flutter ( 5187): The ownership chain for the affected widget is:
I/flutter ( 5187):   InputDecorator ← AnimatedBuilder ← Listener ← _GestureSemantics ← RawGestureDetector ←
I/flutter ( 5187):   GestureDetector ← TextField ← Column ← ExampleWidget ← _ModalScopeStatus ← ⋯
I/flutter ( 5187):
I/flutter ( 5187): When the exception was thrown, this was the stack:
I/flutter ( 5187): #0      debugCheckHasMaterial.<anonymous closure> (package:flutter/src/material/debug.dart:26)
I/flutter ( 5187): #2      debugCheckHasMaterial (package:flutter/src/material/debug.dart:23)
I/flutter ( 5187): #3      InputDecorator.build (package:flutter/src/material/input_decorator.dart:334)
... <output omitted>
I/flutter ( 5187): (elided one frame from class _AssertionError)
I/flutter ( 5187): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter ( 5187): Another exception was thrown: No Material widget found.

115624

小开

最佳答案

错误消息显示:

要引入 Material小部件，您可以直接包含一个, 或者使用包含 Material本身的小部件，例如 Card, Dialog，Drawer，或者 Scaffold。

对你来说，我可能会把你的 Column包在 Scaffold里。这将使之容易添加其他材料小部件到您的应用程序后，如 AppBar，Drawer，或 FloatingActionButton。

@override
Widget build(BuildContext context) {
return new Scaffold(
body: new Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new TextField(
controller: _controller,
decoration: new InputDecoration(
hintText: 'Type something',
),
),
new RaisedButton(
onPressed: () {
showDialog(
context: context,
child: new AlertDialog(
title: new Text('What you typed'),
content: new Text(_controller.text),
),
);
},
child: new Text('DONE'),
),
],
),
);
}

小开

简单的解决办法是:

不使用:

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

你应使用:

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

希望这个能帮到你！

小开

这个错误意味着你必须将这个柱子封装在一个 Materials widget 中，你可以将它作为一个主体放在脚手架上，或者将它作为 Materialapp 的家。例如:

 return MaterialApp(
home: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
TextField(
controller: _controller,
decoration: new InputDecoration(hintText: 'Type something'),
),
]
),
);

或者

return MaterialApp(
body: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
TextField(
controller: _controller,
decoration: new InputDecoration(hintText: 'Type something'),
),
]
),
);

小开

在我的案例中，我在脚手架中使用了一个英雄小部件，就像这样

Scaffold(
body:Hero(
child:ListView(
children:<Widget>[
TextField(),
...
...
]
)
)
);

我只是将 Hero 部件移到了脚手架外面，它就解决了这个问题

Hero(
child:Scaffold(
body:ListView(
children:<Widget>[
TextField(),
...
...
]
)
)
);

小开

把你的小部件放在脚手架里，像这样:

    import 'package:flutter/material.dart';


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


class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Demo',
//home: MyWidget(), --> do not do this !!!
home: Home() --> this will wrap it in Scaffold
);
}
}


class Home extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Demo'),
),
body: MyWidget()); --> put your widget here
}
}


class MyWidget extends StatefulWidget {
...

小开

这可能是由错误的路线引起的。

一个一个检查你们的路线。

小开

只要用 Material widget包装您的 Widget，就可以解决问题。

Material(
child: InkWell(
onTap: onPressed,));

小开

取代 InkWell使用 GestureDetector小部件，对我来说是固定的问题。