以下是一个简单的代码(在 main.dart 中),我试图用来回顾几个月前所做的Flutter基础知识。
在这里,在下面的代码中setState()无法按预期工作,并且原因是状态错误。
我可以通过创建单独的statefulwidget使其具有状态,这些状态构成按钮和文本更改的以下元素。
但是我想知道在下面的代码中进行最小的更改是否可以匿名进行
import 'package:flutter/material.dart';
var textStrings = ["Hello", "Hi", "Hey", "Aloha"];
var counter = 0;
void main() => runApp(MaterialApp(
title: "Hello",
home: Scaffold(
appBar: AppBar(
title: Text(
"First App",
style: TextStyle(
color: Colors.white70,
fontSize: 20,
fontStyle: FontStyle.normal),
),
),
body: Container(
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Padding(padding: EdgeInsets.only(top: 20)),
Card(
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Padding(padding: EdgeInsets.only(bottom: 20)),
Center(
child: Text("With Flutter, Spread Fluttery",
style: TextStyle(
color: Colors.redAccent,
fontStyle: FontStyle.italic,
fontSize: 30)),
),
Padding(padding: EdgeInsets.only(bottom: 20)),
Icon(
Icons.refresh,
size: 50,
color: Colors.amberAccent,
),
Padding(padding: EdgeInsets.only(bottom: 20)),
Text(textStrings[counter % 4],
style: TextStyle(
color: Colors.black38,
fontSize: 30,
fontStyle: FontStyle.normal)),
Padding(padding: EdgeInsets.only(bottom: 20)),
RaisedButton(
onPressed: () {
setState() {
counter++;
}
},
child: Text("Enter",
style: TextStyle(
color: Colors.teal,
fontSize: 30,
)),
)
],
),
)
],
),
),
),
),
));
答案 0 :(得分:2)
当然,您可以添加几行代码,即可使用StatefulBuilder
。
将容器包装在StatefulBuilder
内,并在按钮的setState(() {} )
方法内更改onPressed
。
void main() => runApp(MaterialApp(
title: "Hello",
home: Scaffold(
appBar: AppBar(
title: Text(
"First App",
style: TextStyle(
color: Colors.white70,
fontSize: 20,
fontStyle: FontStyle.normal),
),
),
body: StatefulBuilder(
builder: (context, setState) {
return Container(
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Padding(padding: EdgeInsets.only(top: 20)),
Card(
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Padding(padding: EdgeInsets.only(bottom: 20)),
Center(
child: Text("With Flutter, Spread Fluttery",
style: TextStyle(
color: Colors.redAccent,
fontStyle: FontStyle.italic,
fontSize: 30)),
),
Padding(padding: EdgeInsets.only(bottom: 20)),
Icon(
Icons.refresh,
size: 50,
color: Colors.amberAccent,
),
Padding(padding: EdgeInsets.only(bottom: 20)),
Text(textStrings[counter % 4],
style: TextStyle(
color: Colors.black38,
fontSize: 30,
fontStyle: FontStyle.normal)),
Padding(padding: EdgeInsets.only(bottom: 20)),
RaisedButton(
onPressed: () {
setState(() {
counter++;
});
},
child: Text("Enter : $counter",
style: TextStyle(
color: Colors.teal,
fontSize: 30,
)),
)
],
),
)
],
),
),
);
},
)),
));
答案 1 :(得分:0)
首先,您需要了解,每当调用 setState()方法时,它将仅重建Stateful Widget和State类的 build()方法状态小部件的代码被执行。
在您的代码中,没有这种有状态的小部件可用,因此 setState()方法没有用。
代码如下:
void main() => runApp(MaterialApp(
title: "Hello",
home: Scaffold(
appBar: AppBar(
title: Text(
"First App",
style: TextStyle(
color: Colors.white70,
fontSize: 20,
fontStyle: FontStyle.normal),
),
),
body: MyAppWidgets(),
),
)
);
class MyAppWidgets extends StatefulWidget {
@override
_MyAppWidgetsState createState() => _MyAppWidgetsState();
}
class _MyAppWidgetsState extends State<MyAppWidgets> {
var textStrings = ["Hello", "Hi", "Hey", "Aloha"];
var counter = 0;
@override
Widget build(BuildContext context) {
return Container(
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Padding(padding: EdgeInsets.only(top: 20)),
Card(
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Padding(padding: EdgeInsets.only(bottom: 20)),
Center(
child: Text("With Flutter, Spread Fluttery",
style: TextStyle(
color: Colors.redAccent,
fontStyle: FontStyle.italic,
fontSize: 30)),
),
Padding(padding: EdgeInsets.only(bottom: 20)),
Icon(
Icons.refresh,
size: 50,
color: Colors.amberAccent,
),
Padding(padding: EdgeInsets.only(bottom: 20)),
Text(textStrings[counter % 4],
style: TextStyle(
color: Colors.black38,
fontSize: 30,
fontStyle: FontStyle.normal)),
Padding(padding: EdgeInsets.only(bottom: 20)),
RaisedButton(
onPressed: () {
setState(() {
counter++;
});
},
child: Text("Enter",
style: TextStyle(
color: Colors.teal,
fontSize: 30,
)),
)
],
),
)
],
),
),
);
}
}
答案 2 :(得分:-1)
我认为没有办法,因为runApp无法使用statefull小部件重绘。这只是您应用程序的起点。
只需在主要方法中更改应用程序的标题并使用热重装,它就不会重新出现在您的结果中,请使用播放按钮(运行按钮),它将起作用。