我刚开始掌握Flutter的窍门，但我不知道如何设置按钮的启用状态。
从文档中，它说将onPressed设置为null来禁用按钮，并给它一个值来启用它。如果按钮在生命周期中继续处于相同的状态，这是没问题的。
我得到的印象是，我需要创建一个自定义的有状态小部件，它将允许我以某种方式更新按钮的启用状态(或onPressed回调)。
我的问题是我该怎么做?这似乎是一个非常简单的要求，但我在文档中找不到任何关于如何做到这一点的东西。
谢谢。
当前回答
这个答案是基于更新的按钮TextButton/ElevatedButton/OutlinedButton颤振2.x
不过，按钮是基于onPressed属性启用或禁用的。如果该属性为空，则按钮将被禁用。如果你将函数分配给onPressed，那么按钮将被启用。 在下面的代码片段中，我展示了如何启用/禁用按钮，并相应地更新它的样式。
这篇文章也说明了如何将不同的风格应用到新的 颤振2。x按钮。
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,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
bool textBtnswitchState = true;
bool elevatedBtnSwitchState = true;
bool outlinedBtnState = true;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Padding(
padding: const EdgeInsets.all(16.0),
child: Column(
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
TextButton(
child: Text('Text Button'),
onPressed: textBtnswitchState ? () {} : null,
style: ButtonStyle(
foregroundColor: MaterialStateProperty.resolveWith(
(states) {
if (states.contains(MaterialState.disabled)) {
return Colors.grey;
} else {
return Colors.red;
}
},
),
),
),
Column(
children: [
Text('Change State'),
Switch(
value: textBtnswitchState,
onChanged: (newState) {
setState(() {
textBtnswitchState = !textBtnswitchState;
});
},
),
],
)
],
),
Divider(),
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
ElevatedButton(
child: Text('Text Button'),
onPressed: elevatedBtnSwitchState ? () {} : null,
style: ButtonStyle(
foregroundColor: MaterialStateProperty.resolveWith(
(states) {
if (states.contains(MaterialState.disabled)) {
return Colors.grey;
} else {
return Colors.white;
}
},
),
),
),
Column(
children: [
Text('Change State'),
Switch(
value: elevatedBtnSwitchState,
onChanged: (newState) {
setState(() {
elevatedBtnSwitchState = !elevatedBtnSwitchState;
});
},
),
],
)
],
),
Divider(),
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
OutlinedButton(
child: Text('Outlined Button'),
onPressed: outlinedBtnState ? () {} : null,
style: ButtonStyle(
foregroundColor: MaterialStateProperty.resolveWith(
(states) {
if (states.contains(MaterialState.disabled)) {
return Colors.grey;
} else {
return Colors.red;
}
},
), side: MaterialStateProperty.resolveWith((states) {
if (states.contains(MaterialState.disabled)) {
return BorderSide(color: Colors.grey);
} else {
return BorderSide(color: Colors.red);
}
})),
),
Column(
children: [
Text('Change State'),
Switch(
value: outlinedBtnState,
onChanged: (newState) {
setState(() {
outlinedBtnState = !outlinedBtnState;
});
},
),
],
)
],
),
],
),
),
);
}
}
其他回答
大多数小部件的启用和禁用功能是相同的。
前，按钮，开关，复选框等。
只需设置onPressed属性，如下所示
onPressed: null返回禁用小部件
onPressed:(){}或onPressed: _functionName返回启用的小部件
这是在Flutter中禁用按钮的最简单的方法是将空值分配给onPressed
ElevatedButton(
style: ElevatedButton.styleFrom(
primary: Colors.blue, // background
onPrimary: Colors.white, // foreground
),
onPressed: null,
child: Text('ElevatedButton'),
),
这个答案是基于更新的按钮TextButton/ElevatedButton/OutlinedButton颤振2.x
不过，按钮是基于onPressed属性启用或禁用的。如果该属性为空，则按钮将被禁用。如果你将函数分配给onPressed，那么按钮将被启用。 在下面的代码片段中，我展示了如何启用/禁用按钮，并相应地更新它的样式。
这篇文章也说明了如何将不同的风格应用到新的 颤振2。x按钮。
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,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
bool textBtnswitchState = true;
bool elevatedBtnSwitchState = true;
bool outlinedBtnState = true;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Padding(
padding: const EdgeInsets.all(16.0),
child: Column(
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
TextButton(
child: Text('Text Button'),
onPressed: textBtnswitchState ? () {} : null,
style: ButtonStyle(
foregroundColor: MaterialStateProperty.resolveWith(
(states) {
if (states.contains(MaterialState.disabled)) {
return Colors.grey;
} else {
return Colors.red;
}
},
),
),
),
Column(
children: [
Text('Change State'),
Switch(
value: textBtnswitchState,
onChanged: (newState) {
setState(() {
textBtnswitchState = !textBtnswitchState;
});
},
),
],
)
],
),
Divider(),
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
ElevatedButton(
child: Text('Text Button'),
onPressed: elevatedBtnSwitchState ? () {} : null,
style: ButtonStyle(
foregroundColor: MaterialStateProperty.resolveWith(
(states) {
if (states.contains(MaterialState.disabled)) {
return Colors.grey;
} else {
return Colors.white;
}
},
),
),
),
Column(
children: [
Text('Change State'),
Switch(
value: elevatedBtnSwitchState,
onChanged: (newState) {
setState(() {
elevatedBtnSwitchState = !elevatedBtnSwitchState;
});
},
),
],
)
],
),
Divider(),
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
OutlinedButton(
child: Text('Outlined Button'),
onPressed: outlinedBtnState ? () {} : null,
style: ButtonStyle(
foregroundColor: MaterialStateProperty.resolveWith(
(states) {
if (states.contains(MaterialState.disabled)) {
return Colors.grey;
} else {
return Colors.red;
}
},
), side: MaterialStateProperty.resolveWith((states) {
if (states.contains(MaterialState.disabled)) {
return BorderSide(color: Colors.grey);
} else {
return BorderSide(color: Colors.red);
}
})),
),
Column(
children: [
Text('Change State'),
Switch(
value: outlinedBtnState,
onChanged: (newState) {
setState(() {
outlinedBtnState = !outlinedBtnState;
});
},
),
],
)
],
),
],
),
),
);
}
}
根据文件:
如果onPressed回调为空，则该按钮将被禁用 默认情况下类似于disabledColor中的平面按钮。
所以，你可以这样做:
RaisedButton(
onPressed: calculateWhetherDisabledReturnsBool() ? null : () => whatToDoOnPressed,
child: Text('Button text')
);
为了禁用任何按钮，如FlatButton, RaisedButton, MaterialButton, IconButton等，你需要做的就是将onPressed和onLongPress属性设置为null。下面是一些按钮的简单示例:
FlatButton (Enabled)
FlatButton(
onPressed: (){},
onLongPress: null, // Set one as NOT null is enough to enable the button
textColor: Colors.black,
disabledColor: Colors.orange,
disabledTextColor: Colors.white,
child: Text('Flat Button'),
),
FlatButton(禁用)
FlatButton(
onPressed: null,
onLongPress: null,
textColor: Colors.black,
disabledColor: Colors.orange,
disabledTextColor: Colors.white,
child: Text('Flat Button'),
),
RaisedButton(启用)
RaisedButton(
onPressed: (){},
onLongPress: null, // Set one as NOT null is enough to enable the button
// For when the button is enabled
color: Colors.lightBlueAccent,
textColor: Colors.black,
splashColor: Colors.blue,
elevation: 8.0,
// For when the button is disabled
disabledTextColor: Colors.white,
disabledColor: Colors.orange,
disabledElevation: 0.0,
child: Text('Raised Button'),
),
RaisedButton(禁用)
RaisedButton(
onPressed: null,
onLongPress: null,
// For when the button is enabled
color: Colors.lightBlueAccent,
textColor: Colors.black,
splashColor: Colors.blue,
elevation: 8.0,
// For when the button is disabled
disabledTextColor: Colors.white,
disabledColor: Colors.orange,
disabledElevation: 0.0,
child: Text('Raised Button'),
),
IconButton (Enabled)
IconButton(
onPressed: () {},
icon: Icon(Icons.card_giftcard_rounded),
color: Colors.lightBlueAccent,
disabledColor: Colors.orange,
),
IconButton(禁用)
IconButton(
onPressed: null,
icon: Icon(Icons.card_giftcard_rounded),
color: Colors.lightBlueAccent,
disabledColor: Colors.orange,
),
注意:一些按钮，如IconButton只有onPressed属性。
